U.S. patent number 4,230,990 [Application Number 06/021,567] was granted by the patent office on 1980-10-28 for broadcast program identification method and system.
Invention is credited to John F. Cornelius, John G. Lert, Jr., Peter W. Lert.
United States Patent |
4,230,990 |
Lert, Jr. , et al. |
October 28, 1980 |
**Please see images for:
( Reexamination Certificate ) ** |
Broadcast program identification method and system
Abstract
An automated method and system for identifying broadcast
programs wherein a pattern recognition process is combined with a
signalling event which acts as a trigger signal. At least one such
trigger, or "cue" signal, occurs with each broadcast of every
program which is to be identified; and these signals are used to
activate the pattern recognition process which results in program
identification. These cue signals can either be artificially
inserted into the program signal or they can be events which occur
naturally as part of normal broadcast procedures. A segment of each
program at a predetermined location with respect to one of these
cue signals is sampled and processed according to a feature
extraction algorithm to form the program's reference signature,
which is stored in computer memory. In the field, the monitoring
equipment detects cue signals broadcast by a monitored station and,
upon detection, samples the broadcast program signal at the same
predetermined location with respect to the detected cue and uses
the same feature extraction process to create a broadcast signature
of unknown program identity. By comparing broadcast signatures to
reference signatures, a computer identifies the broadcasts of
programs whose reference signatures have been stored in memory.
Inventors: |
Lert, Jr.; John G. (La Jolla,
CA), Lert; Peter W. (La Jolla, CA), Cornelius; John
F. (Cardiff by the Sea, CA) |
Family
ID: |
21804945 |
Appl.
No.: |
06/021,567 |
Filed: |
March 16, 1979 |
Current U.S.
Class: |
725/22; 348/473;
348/E17.001; 348/E7.024; 382/218; 455/67.13; 725/19; 725/20 |
Current CPC
Class: |
G06K
9/00711 (20130101); H04H 60/37 (20130101); H04H
60/58 (20130101); H04H 60/59 (20130101); H04N
7/08 (20130101); H04N 17/00 (20130101); H04H
2201/90 (20130101) |
Current International
Class: |
H04H
9/00 (20060101); H04H 9/00 (20060101); H04N
17/00 (20060101); H04N 17/00 (20060101); H04N
7/08 (20060101); H04N 7/08 (20060101); H04B
001/00 (); H04B 001/06 (); H04N 007/00 (); G06K
009/00 () |
Field of
Search: |
;358/84,86,142,146,114,122,123 ;325/31,51,53,54,64,308,311 ;343/200
;364/406 ;179/15A,15B ;340/146.3,146.3Q,146.3SQ,146.3Z,146.3AQ |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
G Auerbach, "Pattern Recognition System for Monitoring Video and
Audio Signals," Journal of the SMPTE/3-75, vol. 84. .
J. C. Fletcher, "Teleproof 2: The Technology", Journal of the
SMPTE/3-75, vol. 84, pp. 155-159. .
Jim McDermott, "Electronics Helps Advertisers Keep Track of their
TV Ads", Electronic Design, 3-27-71, pp. 26-28..
|
Primary Examiner: Griffin; Robert L.
Assistant Examiner: Coles; Edward L.
Attorney, Agent or Firm: Dotts, Jr.; Walter M.
Claims
What is claimed as new and desired to be secured by letters patent
of the United States is:
1. The method of identifying certain programs transmitted by a
broadcasting station, wherein at least one predetermined and
readily identifiable signalling event occurs in conjunction with
the broadcast of ones of said programs, said method comprising the
steps of:
generating a digital reference feature set from ones of said
programs by a transformation of at least one segment of a said
program's analog signal content, said segment beginning at a
predetermined time with reference to one of said signalling events
and being of a predetermined duration;
identifying by a label code the program from which each said
reference feature set was derived;
storing a set of said reference feature sets and said associated
program label codes in a memory;
detecting said signalling events within the broadcast signal of
said broadcasting station;
generating a digital broadcast feature set from ones of said
programs broadcast by said broadcasting station, said broadcast
feature set being generated by said transformation of at least one
segment of the analog broadcast signal content, said segment
beginning at a predetermined time with reference to one of said
signalling events and being of a predetermined duration;
comparing at least one said broadcast feature set to at least one
said reference feature set to produce a recognition output when the
degree of similarity between a broadcast feature set and a
reference feature set meets a predetermined standard, the broadcast
program from which said broadcast feature set was derived being
identified by the program label code associated with said reference
feature set.
2. The method of claim 1 further comprising the steps of:
generating a time varying code representative of the actual time in
a predetermined time zone; and
logging an instantaneous value of said time varying code
corresponding to the time of broadcast of each program represented
by said broadcast feature sets.
3. The method of claim 1 wherein at least one said signalling event
is the presence of a predetermined signal within the broadcast
signal of said broadcasting station in conjunction with the
broadcast of ones of said programs by said broadcasting station,
which predetermined signal is absent from the broadcast signal at
at least some other times, further comprising the step of:
inserting said predetermined signal into said broadcast signal.
4. The method of claim 3 wherein at least one said signalling event
is the presence of a predetermined signal within the audio portion
of the broadcast signal.
5. The method of claim 4 wherein said predetermined signal is a
tone of a predetermined frequency and duration.
6. The method of claim 5 wherein the duration of said tone is less
than one half second.
7. The method of claim 3 wherein at least one said signalling event
is the presence of a predetermined signal within the video portion
of the broadcast signal;
8. The method of claim 7 wherein said predetermined signal is
contained within the active picture portion of the video
signal.
9. The method of claim 7 wherein said predetermined signal is
contained within the vertical blanking interval of the video
signal.
10. The method of claim 1 wherein at least one said signalling
event is the absence of a predetermined signal within the broadcast
signal of said broadcasting station in conjunction with the
broadcast of ones of said programs by said broadcasting station,
which predetermined signal is present within the broadcast signal
at at least some other times, further comprising the step of:
deleting said predetermined signal from said broadcast signal.
11. The method of claim 10 wherein at least one said signalling
event is the absence of the program signal within the active
picture portion of the video signal for a predetermined period of
time.
12. The method of claim 10 wherein at least one said signalling
event is the absence of the vertical interval reference signal for
a predetermined period of time.
13. The method of claim 10 wherein at least one said signalling
event is the absence of the vertical interval test signal for a
predetermined period of time.
14. A system for identifying certain programs broadcast by a
broadcasting station, wherein at least one predetermined and
readily identifiable signalling event occurs in conjunction with
the broadcast of ones of said programs, said system comprising:
means for generating a digital reference feature set from ones of
said programs by a transformation of at least one segment of a said
program's analog signal content, said segment beginning at a
predetermined time with reference to one of said signalling events
and being of a predetermined duration, each said reference feature
set being associated with a program label code identifying the
program from which said reference feature set was derived;
means for storing said reference feature sets and said program
label codes;
means for detecting the presence of said signalling events within
the broadcast signal of said broadcasting station;
means activated by said detecting means for generating a digital
broadcast feature set from ones of said programs broadcast by said
broadcasting station, said broadcast feature set being generated by
said transformation of at least one segment of the analog broadcast
signal content, said segment beginning at a predetermined time with
reference to one of said signalling events and being of a
predetermined duration;
means for comparing at least one said broadcast feature set with at
least one said reference feature set stored in said storage means;
and
means for deciding when the similarity between a said broadcast
feature set and a reference feature set meets a predetermined
standard for identification of the broadcast program represented by
said broadcast feature set by the program label code associated
with said reference feature set.
15. A system as recited in claim 14 further including clock means
for generating a time varying code, an instantaneous value of which
is associated with each broadcast feature set, said instantaneous
value representing the time of broadcast of the program from which
said broadcast feature set was derived.
16. The system as recited in claim 14 wherein at least one said
signalling event is the presence of a predetermined signal within
the broadcast signal of said broadcasting station in conjunction
with the broadcast of ones of said programs by said broadcasting
station, which predetermined signal is absent from the broadcast
signal at at least some other times, said system further
comprising:
means for inserting said predetermined signal into said broadcast
signal.
17. The system as recited in claim 16 wherein at least one said
signalling event is the presence of a predetermined signal within
the audio portion of the broadcast signal.
18. The system as recited in claim 17 wherein said predetermined
signal is a tone of a predetermined frequency and duration.
19. The system as recited in claim 18 wherein the duration of said
tone is less than one half second.
20. The system as recited in claim 16 wherein at least one said
signalling event is the presence of a predetermined signal within
the video portion of the broadcast signal;
21. The system as recited in claim 20 wherein said predetermined
signal is contained within the active picture portion of the video
signal.
22. The system as recited in claim 20 wherein said predetermined
signal is contained within the vertical blanking interval of the
video signal.
23. The system as recited in claim 14 wherein at least one said
signalling event is the absence of a predetermined signal within
the broadcast signal of said broadcasting station in conjunction
with the broadcast of ones of said programs by said broadcasting
station, which predetermined signal is present within the broadcast
signal at at least some other times, said system further
comprising:
means for deleting said predetermined signal from said broadcast
signal.
24. The system as recited in claim 23 wherein at least one said
signalling event is the absence of the program signal within the
active picture portion of the video signal for a predetermined
period of time.
25. The system as recited in claim 23 wherein at least one said
signalling event is the absence of the vertical interval reference
signal for a predetermined period of time.
26. The system as recited in claim 23 wherein at least one said
signalling event is the absence of the vertical interval test
signal for a predetermined period of time.
27. A system for identifying certain programs transmitted by
broadcasting stations, wherein at least one predetermined and
readily identifiable signalling event occurs in conjunction with
the broadcast of ones of said programs, said system comprising:
a plurality of monitoring units each capable of receiving
broadcasts from at least one of said broadcasting stations, each
monitoring unit including means for detecting said signalling
events, each monitoring unit further including means responsive to
said detecting means for generating a digital broadcast feature set
from ones of said programs broadcast by said broadcasting station,
said broadcast feature set being generated by a transformation of
at least one segment of the analog broadcast signal content, said
segment beginning at a predetermined time with reference to one of
said signalling events and being of a predetermined duration, said
monitoring unit further including means for storing said broadcast
feature sets;
a central office facility including means for selectively
communicating with ones of said monitoring units and for retrieving
the information stored in said storage means;
means associated with said central office facility for generating a
digital reference feature set from ones of said programs by said
transformation of at least one segment of a said program's analog
signal content, said segment beginning at said predetermined time
with reference to one of said signalling events and being of said
predetermined duration, each said reference feature set being
associated with a label code identifying the program from which
said reference feature set was derived;
means associated with said central office facility for storing ones
of said reference feature sets and said program label codes;
means associated with said central office facility for comparing at
least one said broadcast feature set with at least one said
reference feature set to produce a recognition output when the
degree of similarity between a broadcast feature set and a
reference feature set meets a predetermined standard, thereby
identifying the broadcast program from which said broadcast feature
set was derived by the label code associated with said reference
feature set.
28. A system as recited in claim 27, each said monitoring unit
further including clock means for generating a time varying code,
an instantaneous value of which is associated with each broadcast
feature set, said instantaneous value representing the time of
broadcast of the program from which said broadcast feature set was
derived.
29. The system as recited in claim 27 wherein at least one said
signalling event is the presence of a predetermined signal within
the broadcast signal of said broadcasting station in conjunction
with the broadcast of ones of said programs by said broadcasting
station, which predetermined signal is absent from the broadcast
signal at at least some other times, said system further
comprising:
means for inserting said predetermined signal into said broadcast
signal.
30. The system as recited in claim 29 wherein at least one said
signalling event is the presence of a predetermined signal within
the audio portion of the broadcast signal.
31. The system as recited in claim 30 wherein said predetermined
signal is a tone of a predetermined frequency and duration.
32. The system as recited in claim 31 wherein the duration of said
tone is less than one half second.
33. The system as recited in claim 29 wherein at least one said
signalling event is the presence of a predetermined signal within
the video portion of the broadcast signal.
34. The system as recited in claim 33 wherein said predetermined
signal is contained within the active picture portion of the video
signal.
35. The system as recited in claim 33 wherein said predetermined
signal is contained within the vertical blanking interval of the
video signal.
36. The system as recited in claim 27 wherein at least one said
signalling event is the absence of a predetermined signal within
the broadcast signal of said broadcasting station in conjunction
with the broadcast of ones of said programs by said broadcasting
station, which predetermined signal is present within the broadcast
signal at at least some other times, said system further
comprising:
means for deleting said predetermined signal from said broadcast
signal.
37. The system as recited in claim 36 wherein at least one said
signalling event is the absence of the program signal within the
active picture portion of the video signal for a predetermined
period of time.
38. The system as recited in claim 36 wherein at least one said
signalling event is the absence of the vertical interval reference
signal for a predetermined period of time.
39. The system as recited in claim 36 wherein at least one said
signalling event is the absence of the vertical interval test
signal for a predetermined period of time.
40. A system for identifying certain programs transmitted by
broadcasting stations, wherein at least one predetermined and
readily identifiable signalling event occurs in conjunction with
the broadcast of ones of said programs, said system comprising:
a plurality of monitoring units each capable of receiving
broadcasts from at least one of said broadcasting stations, each
said monitoring unit including means for detecting said signalling
events, each said monitoring unit further including means
responsive to said detecting means for generating a digital
broadcast feature set from ones of said programs broadcast by said
broadcasting station, said broadcast feature set being generated by
a transformation of at least one segment of the analog broadcast
signal content, said segment beginning at a predetermined time with
reference to one of said signalling events and being of a
predetermined duration, each said monitoring unit further incuding
means for storing said broadcast feature sets;
a set of digital reference feature sets stored in said storage
means in ones of said monitoring units, each said reference feature
set having been generated from one of said programs by said
transformation of at least one segment of a said program's analog
signal content, said segment beginning at said predetermined time
with reference to one of said signalling events and being of said
predetermined duration, each said reference feature set being
associated with a label code identifying the program from which
said reference feature set was derived;
means associated with ones of said monitoring units for comparing
at least one said broadcast feature set with at least one said
reference feature set to produce a recognition output when the
degree of similarity between a broadcast feature set and a
reference feature set meets a predetermined standard, thereby
identifying the broadcast program from which said broadcast feature
set was derived by the label code associated with said reference
feature set.
41. A system as recited in claim 40, each said monitoring unit
further including clock means for generating a time varying code,
an instantaneous value of which is associated with each broadcast
feature set, said instantaneous value representing the time of
broadcast of the program from which said broadcast feature set was
derived.
42. The system as recited in claim 40 wherein at least one said
signalling event is the presence of a predetermined signal within
the broadcast signal of said broadcasting station in conjunction
with the broadcast of ones of said programs by said broadcasting
station, which predetermined signal is absent from the broadcast
signal at at least some other times, said system further
comprising:
means for inserting said predetermined signal into said broadcast
signal.
43. The system as recited in claim 42 wherein at least one said
signalling event is the presence of a predetermined signal within
the audio portion of the broadcast signal.
44. The system as recited in claim 43 wherein said predetermined
signal is a tone of a predetermined frequency and duration.
45. The system as recited in claim 44 wherein the duration of said
tone is less than one half second.
46. The system as recited in claim 42 wherein at least one said
signalling event is the presence of a predetermined signal within
the video portion of the broadcast signal;
47. The system as recited in claim 46 wherein said predetermined
signal is contained within the active picture portion of the video
signal.
48. The system as recited in claim 46 wherein said predetermined
signal is contained within the vertical blanking interval of the
video signal.
49. The system as recited in claim 40 wherein at least one said
signalling event is the absence of a predetermined signal within
the broadcast signal of said broadcasting station in conjunction
with the broadcast of ones of said programs by said broadcasting
station, which predetermined signal is present within the broadcast
signal at at least some other times, said system further
comprising:
means for deleting said predetermined signal from said broadcast
signal.
50. The system as recited in claim 49 wherein at least one said
signalling event is the absence of the program signal within the
active picture portion of the video signal for a predetermined
period of time.
51. The system as recited in claim 49 wherein at least one said
signalling event is the absence of the vertical interval reference
signal for a predetermined period of time.
52. The system as recited in claim 49 wherein at least one said
signalling event is the absence of the vertical interval test
signal for a predetermined period of time.
53. A system for identifying certain programs transmitted by
broadcasting stations, wherein at least one predetermined and
readily identifiable signalling event occurs in conjunction with
the broadcast of ones of said programs, said system comprising:
a plurality of monitoring units, each capable of receiving the
broadcasts of at least one of said broadcasting stations, each
monitoring unit including means for recording at least some of the
broadcast signal content from said monitored broadcasting
station;
a central office facility including means for retrieving said
recorded broadcast signal content from ones of said monitoring
units;
means associated with said central office facility for detecting
the presence within said recorded broadcast signal content of said
signalling events;
means associated with said central office facility and responsive
to said detecting means for generating a digital broadcast feature
set from ones of said programs broadcast by said broadcasting
stations and recorded by said monitoring units, said broadcast
feature set being generated by a transformation of at least one
segment of the analog broadcast signal content, said segment
beginning at a predetermined time with reference to one of said
signalling events and being of a predetermined duration;
means associated with said central office facility for generating a
digital reference feature set from ones of said certain programs by
said transformation of at least one segment of a said program's
analog signal content, said segment beginning at said predetermined
time with reference to one of said signalling events and being of
said predetermined duration, each said reference feature set being
associated with a label code identifying the program from which
said reference feature set was derived;
means associated with said central office facility for comparing at
least one said broadcast feature set with at least one said
reference feature set to produce a recognition output when the
degree of similarity between a broadcast feature set and a
reference feature set meets a predetermined standard, thereby
identifying the broadcast program from which said broadcast feature
set was derived by the label code associated with said reference
feature set.
54. A system as recited in claim 53, each said monitoring unit
further including clock means for generating a time varying code
which is recorded on said recording means, an instantaneous value
of which time varying code is associated with each broadcast
feature set, said instantaneous value representing the time of
broadcast of the program from which said broadcast feature set was
derived.
55. The system as recited in claim 53 wherein ones of said
monitoring units further include means for detecting said
signalling event and producing a detection output which is recorded
on said recording means, said recorded detection output being
detected by said detecting means associated with said central
office facility to identify the presence of said signalling
events.
56. The system as recited in claim 53 wherein ones of said
monitoring units further include means for detecting said
signalling event and means responsive to said detecting means for
controlling the operation of said recording means.
57. The system as recited in claim 53 wherein at least one said
signalling event is the presence of a predetermined signal within
the broadcast signal of said broadcasting station in conjunction
with the broadcast of ones of said programs by said broadcasting
station, which predetermined signal is absent from the broadcast
signal at at least some other times, said system further
comprising:
means for inserting said predetermined signal into said broadcast
signal.
58. The system as recited in claim 57 wherein at least one said
signalling event is the presence of a predetermined signal within
the audio portion of the broadcast signal.
59. The system as recited in claim 58 wherein said predetermined
signal is a tone of a predetermined frequency and duration.
60. The system as recited in claim 59 wherein the duration of said
tone is less than one half second.
61. The system as recited in claim 57 wherein at least one said
signalling event is the presence of a predetermined signal within
the video portion of the broadcast signal .
62. The system as recited in claim 61 wherein said predetermined
signal is contained within the active picture portion of the video
signal.
63. The system as recited in claim 61 wherein said predetermined
signal is contained within the vertical blanking interval of the
video signal.
64. The system as recited in claim 53 wherein at least one said
signalling event is the absence of a predetermined signal within
the broadcast signal of said broadcasting station in conjunction
with the broadcast of ones of said programs by said broadcasting
station, which predetermined signal is present within the broadcast
signal at at least some other times, said system further
comprising:
means for deleting said predetermined signal from said broadcast
signal.
65. The system as recited in claim 64 wherein at least one said
signalling event is the absence of the program signal within the
active picture portion of the video signal for a predetermined
period of time.
66. The system as recited in claim 64 wherein at least one said
signalling event is the absence of the vertical interval reference
signal for a predetermined period of time.
67. The system as recited in claim 64 wherein at least one said
signalling event is the absence of the vertical interval test
signal for a predetermined period of time.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to methods for automatically
identifying broadcast programs, and more particularly to a
practical and economical method of using computerized pattern
recognition to identify large numbers of programs, such as
commercial advertisements, broadcast by television and radio
stations.
The term "program" is used herein in a generic sense to include any
complete programming entity such as a news or entertainment show, a
commercial, a record, etc. Hundreds of thousands of such programs
are boradcast each day by commercial television and radio stations.
There are many needs for information relating to this broadcasting
activity that can only be satisfied by some form of direct
monitoring of the broadcasts themselves.
For example, advertisers need information that would verify the
broadcasts of their commercials. Advertising agencies, advertisers,
and broadcasters need information relating to the scope, volume,
and timing of broadcasts of commercials. Performing artists need
data relating to payments of residuals and royalties. Program
suppliers need verification of broadcaster compliance with
provisions of contrasts for purchases of program rights. Record
companies need information relating to the amount of air-play of
records. And networks need information concerning broadcasts (or
"clearances") by affiliated stations of network programming.
These needs have never been fully nor economically met by manual
monitoring efforts. Moreover, the automated systems that heretofore
have been developed have either failed to perform reliably and
economically, have caused unacceptable degradation of the program
quality, or have resulted in inefficient use of limited spectrum
space.
2. Description of the Prior Art
There have been two general methods used in developing these
automatic program identification systems in the prior art:
identification encoding, and pattern recognition.
Method A: Identification Encoding
Method A includes program identification systems that require the
transmission of some type of ancillary signal that contains coded
information which uniquely identifies the coded program. For such a
system to be acceptable to both the industry and the Federal
Communications Commission (FCC), it must satisfy two fundamental
requirements: (1) the ancillary signal must not cause any
degradation in the program quality, and (2) the system must be
extremely reliable. In addition, in order to maximize the public
benefit of the scarce and valuable resource represented by
available information capacity within the broadcast signal, the FCC
will require that the ancillary signal occupy the absolute minimum
amount of spectrum space necessary to provide the program
identification service.
In order to monitor the broadcasts of television commercials, which
are distributed on both film and videotape, the ancillary signal
must be multiplexed with the actual program signal so as to be
compatible with both recording media. To avoid program degradation,
the ancillary signal must be totally imperceptible to the human
audience. Such signals are referred to as "subliminal" signals.
Attempts to develop subliminal identification coding have failed to
satisfy the two the fundamental requirements of program
non-degradation and reliability.
One such attempt, developed by International Digisonics Corporation
of Chicago, Ill. and described in the Journal of the Society of
Motion Picture and Television Engineers (SMPTE), vol. 84, number 3,
p. 160 (March, 1975), used a digital code, in the form of vertical
bar (or "picket fence") patterns, which was time-multiplexed with
the program video signal. Code patterns were inserted into the four
corners of the rectangular picture raster, where they were to be
hidden from view on home television sets by the rounded corners of
the mask in front of the screen. However, it was found that some
film playback equipment used by broadcasters allowed frames to
shift laterally to such an extent that the vertical bars drifted
into the visible picture area, causing significant degradation in
program quality as well as loss of coded information and system
error.
Another attempted invention of a system compatible with both film
and tape was by Audicom Corporation of New York, N.Y. (U.S. Pat.
No. 3,845,391; Crosby). This approach involved a digital code
frequency-multiplexed with the program audio signal; the coding
method was frequency shift keying. Audio encoding has the
additional advantage of being compatible with both television and
radio broadcasting. In order to avoid program degradation, the
ancillary signal was to be submerged at a sufficiently low level to
be inaudible to the listener.
However, in tests conducted by a working group of the SMPTE and
reported in the final report of the Ad Hoc Committe on Television
Broadcast Ancillary Signals of the Joint Committe on Intersociety
Coordination (published May, 1978), this system failed to satisfy
either one of the two fundamental requirements. Program
identification was found to be extremely unreliable, apparently
because the ancillary signal was submerged at such a low level that
the noise added in transmission through the broadcasting system
pushed the noise-to-signal ratio beyond the tolerances of the
decoding equipment. Even at this low level, however, the ancillary
signal resulted in significant degradation of program signal
quality. Listener tests revealed that some of the codes were
audible, while others caused noticeable distortion of the program
audio. A significant factor in this degradation appears to be the
duration of the encoding: approximately 3 seconds were required to
transmit a uniquely identifying digital code, which is quite a long
time to the human ear.
If a system is intended only to monitor broadcasts of network
programs, compatibility with film and tape is not necessary since
videotape is the only medium used to record programs for delayed
broadcast. In this case, the ancillary signal could be contained in
a part of the vertical blanking interval where it would not cause
any imaging on a viewer's screen, thereby avoiding any problem of
degradation of picture quality. This is the approach used in a
system developed by the A. C. Nielsen Company of Northbrook, Ill.
for network clearance monitoring (U.S. Pat. No. 4,025,851;
Haselwood et al), wherein digital coding is placed onto line 20 in
the vertical blanking interval.
If reliable, this approach would satisfy the two fundamental
requirements. However, line 20 is the only line in the vertical
blanking interval approved by the FCC for carrying radiated
ancillary signals which has not yet been reserved for some other
purpose, and it is not clear that additional lines will become
available in the future. The Nielsen system would thus pre-empt
valuable spectrum space that could be used for other purposes that
would provide much broader public benefit. This raises the crucial
public-interest issue of whether the same program-identification
service could be provided with more efficient use of spectrum
space.
In all of these examples, the time duration of the program
identification encoding proved to be problematical in some way.
Indeed, a fundamental problem of Method A is that the extent of the
time domain that must be used to communicate sufficient information
to identify each program uniquely turns out to be quite
significant, resulting in a high probability of program degradation
or in use of scarce spectrum space to valuable to devote to this
purpose.
Another potential problem of a monitoring system using ancillary
identification encoding is that it would be possible for a
dishonest broadcaster to gain financially by counterfeiting such
codes. For example, the broadcaster might sell the same commercial
spot to both a national advertiser, who encodes commercials, and to
a local advertiser who does not encode. By inserting the
identification code from the national commercial into the broadcast
of the local commercial, the broadcaster would cause the monitoring
system to identify the broadcast program incorrectly and could
could bill for both commercials, thereby defrauding the national
advertiser. Or, if the station is a network affiliate, the
broadcaster might "clip", or pre-empt, a network commercial or even
a portion of a network program in order to broadcast a local
commercial; but by counterfeiting the network code, he could cause
the monitoring system to confirm correct clearance of the network
signal.
There is another technology that can be used to identify programs
without the use of identification encoding. This approach is used
by the present invention. Further background discussion is
therefore necessary to show how this second method in the prior art
set the stage for the present invention.
Method B: Computerized Pattern Recognition
As an alternative to adding codes to the program material, the
prior art includes a method of program identification whereby the
audio or video program signal is analyzed in such a way that the
program supplies its own unique code. Method B, therefore includes
all attempts to solve the problem of automated broadcast monitoring
solely through the use of computerized pattern recognition.
Pattern recognition consists of two basic processes: feature
extraction and classification. The feature extraction process is
applied to the program signal to produce a digital signature of a
given program: certain features of the program signal are measured,
and these measured values are used to characterize that program.
The analog program signal is normally digitized by being passed
through an analog-to-digital converter, and program information
(either audio or video) is sampled and processed using some
non-linear transform (which can be done either digitally or in
analog) to produce a digital data set which is essentially unique
to a particular program. Such a data set is commonly referred to as
a "signature", "feature set", or "feature vector", terms which are
to be considered as equivalent and are used interchangeably in this
application.
From each program which is to be identified when broadcast, a
segment of some duration is selected and used in the feature
extraction process to produce the program's "reference" signature.
In the field, program information from the broadcast signal of a
monitored station can be sampled for a like duration and used in
the same feature extraction process to form a "broadcast" signature
of unknown program identity. In the classification process,
broadcast signatures are compared mathematically to reference
signatures in order to identify the occurence of known programs.
When a broadcast signature is sufficiently similar to a reference
signature, the broadcast program is identified as the know
program.
The fundamental problem with a pure pattern recognition approach is
the massive amount of data processing that is required. Program
information in the broadcast signal must be sampled continuously,
and each sample processed according to the feature extraction
algorithm to form a broadcast signature. In the classification
process, each broadcast signature must then be compared iteratively
with reference signatures either until there is a match and a
positive identification, or until the set of reference signatures
is exhausted and the broadcast program is classified as
unidentifiable. Since only a tiny fraction of sampled broadcast
signatures will match a reference signature, the computer is
therefore required to cycle through the entire library of reference
signatures for virtually every sampled broadcast signature.
Furthermore, there are far too many broadcast signatures to store
at the monitoring site and transmit to a central computer for later
classification on an economical basis. Consequently, both feature
extraction and classification processing must take place
concurrently. Thus, a sampled broadcast signature must be compared
to each and every reference signature before the next sample
broadcast signature is formed.
The magnitude of this task depends primarily upon the number of
reference feature signatures in the library, plus the rate at which
sample broadcast signatures are formed and the amount of data in a
signature. In actual commercial practice, the set of reference
signatures will represent thousands of commercials and other
programs. Moreover, the minimum sampling rate and signature size
that will be required for unambiguous classification will be
significant regardless of the particular feature extraction and
classification algorithms used. As a result, the data processing
task is enormous. The computer resources that must be dedicated to
monitoring each station makes this approach economically
impractical.
Consider, for example, the teaching of U.S. Pat. No. 3,919,479
(Moon et al) that resulted in the Identimatch System (Real Time
Technology of Norwood, Mass.). In this system, program audio was
used to form program signatures. The feature extraction process
consisted of an analog non-linear transform, such as full-wave
rectification and low-pass filtering applied to the audio signal to
produce a low-frequency "envelope" waveform, and analog-to-digital
conversion of this transformed waveform. Correlation was the
mathematical method of comparison used in classification. Program
information from an eight-second segment of each commercial's sound
track was used to form the reference signature, and the sampling
rate was quite low, on the order of 50 Hz. Each signature thus
consisted of around 400 numbers.
The audio program signal of each monitored station was processed
using the same non-linear transform, and this broadcast envelope
waveform was sampled at the same 50 Hz rate to form broadcast
signatures of unknown program identity. Each fiftieth of a second,
this process produced a broadcast signature derived from the
preceding 8.0 seconds and consisting of 400 numbers; and each such
signature had to be correlated with the entire library of reference
signatures before the next signature was formed, i.e., in 0.02
second. If this library were to consist of 2,000 reference feature
sets, for example, there would be 100,000 correlations for each
second of the broadcast day. This would require a large computer
simply to monitor a single station. For this reason, the system was
not at all economical.
Another company named Video Image Analysis Corporation (VIAC) of
New York developed a prototype for a pattern recognition monitoring
system, described in general terms in Journal of the SMPTE vol. 84,
number 3, p. 162 (March, 1975). In this system, video program
information was used to form program signatures, though we do not
know the specific feature extraction or classification algorithms
used. It is known, however, that a broadcast signature was formed
from each broadcast frame. Signatures were thus created at a rate
of 30 per second, so the processing task would have been similar to
Identimatch. It is also known that this system was abandoned after
the prototype stage because it became apparent that the
computational requirements would be too great for the system to be
practical or economical.
In neither one of these two inventions, nor anywhere else in the
prior art, is there any teaching that offers a solution to this
practical problem of making the computational task cost-effective
by somehow reducing the amount of data processing required to
identify broadcast programs. The present invention solves this and
other problems and thereby makes the method of computerized pattern
recognition technically feasible and economically viable for the
first time.
Examples of relevant broadcast monitoring systems using ancillary
digital encoding (Method A) found in the prior art are U.S. Pat.
Nos. 3,845,391; 4,025,851; 3,760,275; and a system described in the
Journal of the SMPTE, volume 84, number 3, page 160 (March, 1975).
Examples of systems using pattern recognitions techniques (Method
B) found in the prior art are U.S. Pat. No. 3,919,479 and a system
described in the Journal of the SMPTE, volume 84, number 3, page
162.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a
novel automatic broadcast monitoring system and method with
improved economy.
An additional object is to provide an automatic broadcast
monitoring system and method that minimizes the amount of data
processing required.
A further object is to provide an automatic broadcast monitoring
system and method that requires simpler and less expensive data
processing equipment.
Another object is to provide a novel automatic broadcast monitoring
system and method that does not require the addition of program
identification codes to broadcast signals.
Still another object is to provide a system and method for
automatically monitoring both television and radio broadcasts.
Yet another object is to provide an automatic broadcast monitoring
system and method that can identify programs recorded on any
medium, including film, videotape, audiotape, and discs.
An additional object is to provide a system and method for
automatic broadcast monitoring that is immune to deception by
counterfeit program identification codes.
One further object of the present invention is to provide a
subliminal ancillary audio signal for use in an automated broadcast
monitoring system.
These and other objects are achieved by the present automated
broadcast monitoring method and system wherein a pattern
recognition process is combined with a signalling event which acts
as a trigger signal. At least one such trigger, or "cue" signal,
occurs with each broadcast of every program which is to be
identified; and these signals are used to activate the pattern
recognition process which results in program identification. (The
terms "cue" and "trigger" are used interchangeably in this
application.) These cue signals can either be artificially inserted
into the program signal or they can be events which occur naturally
as part of normal broadcast procedures. A segment of each program
at a predetermined location with respect to one of these cue
signals is sampled and processed according to a feature extraction
algorithm to form the program's reference signature, which is
stored in in computer memory. In the field, the monitoring
equipment detects cue signals broadcast by a monitored station and,
upon detection, samples the broadcast program signal at the same
predetermined location with respect to the detected cue and uses
the same feature extraction process to create a broadcast signature
of unknown program identity. By comparing broadcast signatures to
reference signatures, a computer identifies the broadcasts of
programs whose reference signatures have been stored in memory.
Compared with prior art approaches (Method B) involving continuous
pattern recognition processing, the use of the cue signals
represents a significant improvement in a number of ways.
First, and most importantly, the cue signals differentiate program
segments from which reference signatures have been derived from all
or most of the remaining program information in the broadcast
signal. It is therefore unnecessary to form a program signature
unless and until a cue signal is detected. Feature extraction
processing is selective rather than continuous, so that all or most
of the unidentifiable broadcast signatures are never created. This
represents an enormous reduction in the amount of data processing
required, and, therefore, in computational costs.
Secondly, cue signals provide for accurate registration in
sampling. By using cue signals as synchronizing points of reference
in the time domain, the feature extraction process always uses the
same program information from a given program to form its
signature. This further reduces the amount of broadcast program
information that must be used in pattern recognition
processing.
Thirdly, the cue signals eliminate the need for concurrent feature
extraction and classification processing. Since broadcast
signatures are created selectively and in limited numbers, it now
becomes possible to store them for later classification processing.
For example, remote monitoring devices could simply create and
store broadcast signatures and send them to a central computer
facility for classification. This could decrease the cost of the
monitoring system significantly. Alternatively, if both processes
are to be performed at the monitoring site, classification no
longer must keep pace with feature extraction, which is quiescent
for most of the time. Broadcast signatures could be placed in
buffer storage for classification processing during this idle time,
and classification could take much more time than would have been
possible in the prior art. This means that the library of reference
signatures used in this process could be much larger and more
programs could be broadcast monitored.
For the purposes of this invention, any readily-detectable
signalling event may be used as a cue signal as long as it occurs
every time that a program which is to be identified is broadcast.
It will be seen that there are many possible such signalling
events.
The cue signal may be an "artificial" signal which is inserted into
the program signal specifically for this purpose and is unrelated
to the actual program information, in which case it is, by
definition, an ancillary signal. Alternatively, the cue can be a
"natural" signalling event which occurs as part of normal
broadcasting procedures and which is part of the normal program
signal, such as the start or the end of the program. Such natural
signals are referred to herein as non-ancillary signals.
Non-ancillary signals have the advantage of avoiding any possible
program degradation and, therefore, not requiring FCC approval.
The cue signal can either be "exclusive" or "non-exclusive". If
exclusive, the cue occurs only when a program to be identified is
broadcast. If non-exclusive, it can occur at other times as well,
as long as it occurs each time that a program which is to be
identified is broadcast. However, the more exclusive the cue signal
is, the more useful it will be in differentiating broadcast
programming, the fewer unidentifiable signatures will be formed,
and the less data processing will be required.
Moreover, the cue signal can be either a "positive" or a "negative"
signal. A positive cue is the presence of a signal which is
normally absent; a negative cue is the absence of a signal which is
normally present.
In television, the cue signal may be placed in either the audio or
video portions of the broadcast signal, but in radio, placement is
obviously limited to the audio. If in the video, the cue signal can
be contained either in the active picture raster or in the vertical
blanking interval.
Some examples of possible signalling events which can be used as
cue signals are discussed below. One such signalling event might be
a pure tone of a certain frequency and duration inserted into the
sound track of programs to be identified but virtually never
present otherwise. This would be a positive, exclusive, audio cue
signal and would have the broadcast possible utility since it would
be compatible with all recording and broadcasting media. A similar
type of cue, but video rather than audio, would be an image of a
certain shape and size in the picture raster. In most cases, such
positive, exclusive, audio or video cue signals will be ancillary
signals and therefore must be subliminal. In some instances,
however, such signals can be non-ancillary and, therefore,
perceptible to the human audience. For example, an ideal
non-ancillary cue signal for monitoring network clearances is an
audio or video network logo, which signals to the audience the
identity of the network and occurs with virtually every network
show.
In order to signal to the audience a transition from one program to
another, broadcasters separate the end of one program signal from
the beginning of another by "dead air", i.e., blank frames. Such
program changes can be detected by analyzing the broadcast signal
for the presence or absence of the program signal. Thus, a blank
field which is followed by a field containing picture information
indicates the start of a program, and a picture field followed by a
blank field signals the end of a program. Each of these
non-ancillary signalling events can be used as a cue signal because
they always occur when a program which is to be identified is
broadcast, even though they occur at other times as well. Since a
blank field is the absence of the normally present program signal,
this would be a negative, non-ancillary, non-exclusive, video cue
signal in the picture raster. (Even when not used as cue signals,
such program-start and program-stop signals are very useful in
measuring program duration and in identifying the existence of
"strings" of commercials.)
Another possible negative cue signal is the absence of the normally
present vertical interval reference signal (VIRS) on line 19 or the
vertical interval test signal (VITS) on line 17 for a predetermined
period of time (e.g., one field) only when a program which is to be
identified is broadcast. This would be an ancillary, negative,
exclusive, video cue signal in the vertical blanking interval. The
same type of signal, except positive rather than negative, would be
the presence of a signal on an otherwise unused portion of a line
in vertical blanking interval, such as line 20.
It should also be noted that more than one cue signal can be used
in combination in the present invention. For example, a single
network logo appearing in a program would alert the system that a
network program which is to be identified is being broadcast, but
the actual sampling and feature extraction processes would be
initiated only upon the detection of program changes within the
program, such as those occuring as a result of commercial
breaks.
While some of these cue signals are positive ancillary signals such
as those used in Method A of the prior art, the program
identification codes of Method A are absent, their function being
accomplished by pattern recognition processing. The information
content of the ancillary signal is thus reduced to the absolute
minimum. The amount of the time domain occupied by the signal is
thereby also reduced to the minimum necessary for detection. This
invention thus eliminates the time-domain problems encountered in
the prior art. For example, a positive cue signal in the vertical
blanking interval would occupy a much smaller portion of a scanning
line than Haselwood, thereby preempting much less of this valuable
spectrum space. An audio cue signal, on the other hand, would solve
the audibility problem by reducing the time duration of the signal
to such an extent that absolute audibility threshold would
increase, and by allowing the signal to be masked effectively by
program audio.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention, and its method of operation, together with
additional objects and advantages thereof, can be better understood
by reference to the following detailed description considered in
connection with the accompanying drawings wherein:
FIG. 1 is a block diagram of a broadcast monitoring system,
including sub-systems for monitoring both network- and
station-originated broadcasts, according to the method of the
present invention;
FIG. 2 is a block diagram of a remote field monitor of a broadcast
monitoring system according to the invention;
FIG. 3 is a block diagram of a video cue detector according to the
invention;
FIG. 4 is a block diagram of a program-change detector according to
the invention;
FIG. 5 is a block diagram of a video cue inserter according to the
invention, wherein the cue is a signal in the active picture raster
of the television signal;
FIG. 6 is a block diagram of a video cue inserter according to the
invention, wherein the cue is a signal in the vertical blanking
interval of the television signal; and
FIG. 7 is a block diagram of an audio cue inserter according to the
invention.
FIG. 8 is a block diagram of an alternative embodiment of a field
monitor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, wherein like reference numerals
designate the same or corresponding parts throughout the several
views, FIG. 1 shows in block diagram the overall operation of a
broadcast monitoring system according to the invention. This system
includes two sub-systems, as shown: one for monitoring
network-originated programs 2 and another for monitoring
(pre-recorded) station-originated programs 4.
In the first, programs 6 are distributed to a number of
broadcasting stations from a central programming source, the
network. A program 6 can either be live or recorded on some medium
such as film, tape, or disc. From this program 6 is generated an
analog signal 8 containing the program information.
If an ancillary cue signal is used, insertion of cues into the raw
program signal 8 is accomplished by means of a cue inserter 14 at
the time of network origination. (If the program 6 is pre-recorded,
cue insertion can be done as part of the production process.) In
either case, the final program signal 16 originated by network
control 18 will contain at least one cue signal for each network
program 6. (If the cue signal is a non-ancillary signal, the final
program signal 16 containing cue signals will be the same as the
raw program signal 8 generated from the original program 6.) This
final program signal 16 is distributed from network control 18 to
an affiliated broadcasting station 20.
It should be noted at this point that the term "program signal" is
used throughout this application to designate either the composite
video signal or the audio signal, or even both, where appropriate.
(These components of the program signal are not shown in FIG. 1.)
Thus, the raw program signal 8 can include a video component 7
and/or an audio component 9; similarly, the final program signal 16
can refer to either a composite video signal 15 or an audio signal
17 (or both) which include cue signals.
Each network program 6 is registered for monitoring at the time of
its origination. The registration unit 22 analyzes this network
program signal 16 as it is fed into the distribution system. When a
cue signal is detected within the signal 16, a feature extraction
process is performed by the registration unit 22, which results in
the creation of a reference signature for each network program. A
real-time clock is also read and a digital time code representing
the time of program origination is associated with each reference
program signature. These reference signatures and associated
time-of-origination codes, along with program identification labels
and any other data necessary to provide the various monitoring
services, are entered into the system's central computer 28 and
stored in memory.
The broadcasting station 20 can either broadcast a network program
at the time it comes in on the network feed, or record it on
videotape and broadcast it later (delay broadcast), or not
broadcast it at all. Whenever a network program is broadcast by a
monitored broadcasting station 20, its broadcast signal 24 will be
received by a field monitor 26, which continuously examines this
signal 24 for the presence of cue signals. When a cue is detected,
the field monitor 26 executes the same feature extraction process
to derive a broadcast signature of unknown program identity. A
real-time clock is read and a digital time code representing the
time of program broadcast is associated with each broadcast
signature. If the cue signal is other than a program start or stop,
the monitor also detects all such program changes, simply noting
the time of each.
By means of a telecommunications link 27, these broadcast program
signatures and associated time-of-broadcast codes are transfered to
the system's central computer 28, which identifies each broadcast
program by means of a classification process wherein each broadcast
signature is compared to one or more reference signatures.
There are two modes of classification processing: verification and
recognition. The verification mode is used when an unidentified
program is supposed to be a certain known program; its signature is
simply compared to the reference signature of the presumed known
program to verify its identity. The recognition mode is used when
there is no basis for such a presumption of identity, in which case
the unidentified signature must be compared iteratively with
reference signatures either until there is a match and the program
is identified or until the set of reference signatures is exhausted
and the program is classified as unidentifiable. Obviously, if the
verification mode results in positive identification, it requires
much less data processing than the recognition mode, so it is
always done first.
In the network monitoring system 2, the broadcast schedules of most
programs are known in advance, so most of the classification
processing is in the verification mode. Classification takes place
in three stages, the first two of which are verification. At each
stage, whenever the broadcast of a network program is identified,
both the broadcast signature and the reference signature are
eliminated from all further processing.
The first stage identifies programs that have been broadcast
directly from the network feed. Each reference signature generated
during network programming is compared to the broadcast signature
whose time-of-broadcast time code is the same as the
time-of-origination code of the origination signature. A positive
verification indicates a real-time clearance of the program. Most
broadcasts of network programs are identified at this stage.
Classification then proceeds to identify delayed broadcasts. The
set of reference signatures used in this processing includes those
from network programs whose clearance had not been verified in the
first stage, plus all programs that had been fed to the station
during the previous week but which had not yet been broadcast.
Since changes in a station's broadcasting schedule occur relatively
infrequently, the times of most delayed broadcasts are known from
prior experience. The second stage of classification processing is
thus also in the verification mode: the broadcast signature created
at the time of each presumed delayed broadcast is compared to the
reference signature of the assumed network program.
In the final stage, classification processing switches to the
recognition mode in order to identify unusual delayed broadcasts.
Each remaining broadcast signature is compared to remaining
reference signatures either until the broacast program is
identified or until the set of reference signatures is
exhausted.
Referring again to FIG. 1, in the sub-system 4 for monitoring
station-originated broadcasts of pre-recorded programs such as
"spot" commercials, cue signals (if ancillary) are inserted into
all programs to be identified as the last step in producing the
program master 30. Either the video 7 or audio 9 portion of the
program signal 8 is applied to a cue inserter 14, which adds a cue
signal at one or more locations within the program signal 8. The
output of the cue inserter 14, which is the final program signal 16
containing cues, is recorded by means of the recorder 29. This
recording 30 is the program master from which all program copies 32
distributed for broadcast are duplicated.
A copy 32 of each such program is applied to a registration unit
22, which detects the cue signals contained therein and thereupon
executes a feature extraction process to form a reference signature
for the program. This reference signature is entered into the
system's central computer 28 and stored in memory.
When a program copy 32 containing one or more cue signals is
broadcast by a monitored broadcasting station 20, cue signals are
detected within the station's broadcast signal 24 by the field
monitor 26, which functions in the same way as described above with
reference to the network monitoring sub-system 2, creating and
collecting broadcast signatures of unknown program identity and
time-of-broadcast codes. This data is entered into the system's
central computer 28, which performs the classification processing
to determine the identity of broadcast programs. In this case,
however, the broadcast schedules of most programs are not known in
advance, so virtually all classification is in the recognition
mode.
(Note that the term "broadcast" is used in this discussion
primarily to mean over-the-air radiation of the transmitted signal.
However, it should be recognized that the present invention would
work equally well in a system where the distribution of the
broadcast signal is by cable or other non-radiated means. Hence, in
terms of the applicability of the present monitoring system and
method, the word "broadcast" as used herein should be considered to
include any form of electronic distribution of a program signal
from one point to another. Another point worth mentioning is that,
while FIG. 1 shows the field monitor 26 receiving a radiated signal
24 at a site remote to the broadcasting station, it would clearly
be possible to locate the monitor 26 on the broadcaster's
premises.)
In FIG. 2 is shown the preferred embodiment of a field monitor 26
according to the invention. The broadcast signal 24 from a
monitored broadcasting station 20 is acquired by the receiving
antenna 50 and fed to a receiver 52, which includes a tuner and
amplifier. The output of the receiver 52, which is the program
signal 16 containing cue signals, is then fed to a cue detector 58,
a program-change detector 60, and a data acquisition module 56. If
the feature extraction algorithm calls for some form of signal
preconditioning, such as filtering or rectification, the program
signal 16 first passes through a preconditioning module 54 prior to
reaching the data acquisition module 56. The cue detector 58, the
program-change detector 60, and the data acquisition module 56 all
output to a computer 62.
When the computer 62 receives detection output 59 from the cue
detector 58 indicating the presence of a cue signal, it enables the
data acquisition module 56 and takes from this module 56 digitized
program information 57 to be used in forming the broadcast
signature. The computer also reads the output of a real-time clock
68, from which it creates a time-of-broadcast code for the
signature.
The computer 62 can be virtually any minicomputer, such as a PDP 11
computer manufactured by Digital Equipment Corporation of Maynard,
Massachusetts. There are a variety of off-the-shelf component
systems that can be used for the data acquisition module 56, such
as the DT2762 Data Acquisition System manufactured by Data
Translation Incorporated of Natick, Massachusetts, which has a
12-bit analog-to-digital converter with a 35 MHz throughput and a
sample-and-hold module on its input with a 10-nanosecond window to
ensure accuracy at the throughput rate. In the preferred
embodiment, the real-time clock 64 is simply a short wave receiver
tuned to the WWV signal broadcast by the National Bureau of
Standards. This WWV signal is itself a digital time code of
extremely high accuracy, which is read by the computer.
Program information in either the video 15 or audio 17 portions of
the program signal 16 can be used in the feature extraction
process, and there are many feature extraction algorithms that can
be used to form program signatures. In the preferred embodiment,
the audio portion of the program signal 17 is used and the spectral
composition of the audio signal is analyzed. This approach is
advantageous because the spectral composition of the audio program
signal over time is unique to each program and provides a high
degree of unambiguous differentiability. Signal preconditioning 54
consists of bandlimiting by a single pole active filter whose -3 dB
point is 2 KHz, the purpose of which is to restrict the frequencies
being digitized to those most often present in programs to be
identified.
When the computer 62 receives a detection output 59 from the cue
detector 58, it activates the data acquisition module 56 for a
period of four seconds. The data acquisition module 58 digitizes
the bandlimited program audio signal, samples at the rate of 4 kHz,
and passes this data 57 to the computer 62. Each one-second segment
is treated as a separate sample. Thus, the detection of each cue
signal results in the generation of four "blocks" of data each
containing 4096 points, and each point having a value between 0 and
4095. The data is then normalized by setting the largest value in
the entire data set (all four one-second blocks) to 1023 and
adjusting all other values proportionately.
From this sampled program information, the computer 62 forms a
feature set by measuring the relative energy within certain
frequency bands of each one-second block of data. The 4096 points
in each block are divided into 16 sub-blocks of 256 each and the
power spectrum for each sub-block is computed using a standard Fast
Fourier Transform, giving 16 sub-estimates. These sub-estimates are
then averaged to obtain a single, 256-point estimate of the power
spectrum of the entire 1-second block of raw data. This data is
reduced even further by partitioning the power spectrum into 32
frequency bands, and computing the total energy in each band. The
four 32-point feature vectors resulting from each one-second block
of data are concatenated to produce a single 128-point vector,
which is the signature used to characterize the program.
As they are formed, broadcast signatures are stored, along with
time-of-broadcast codes, in a memory device 66 by the computer 62.
Periodically, the central computer 28 polls each field monitor 26
over a telecommunications link 27 by means of the communications
modem 68, collects the accumulated data, and performs the
classification processing to identify the broadcast programs. In
the preferred embodiment, the telecommunications link 27 is a
voice-grade telephone line.
Note that, while in the preferred embodiment the segment from which
program information is sampled follows the cue signal, it could
also precede the cue. In this case, the data acquisition module 56
would run continuously, its output going to a buffer memory capable
of holding 4-seconds worth of digitized program information. Upon
detection of a cue signal, the computer 62 would take the data from
the buffer memory and complete feature extraction.
The function of the program-change detector 60 is to identify the
beginning and end of each program broadcast. The detection output
61 of the program-change detector 60 consists of two types of
signals: a program-start signal is output when at least one blank
field in the program composite video signal 15 is followed by a
picture field, and a program-stop signal is output when at least
one blank field follows a picture field. From the output of the
real-time clock 68, the computer 62 determines the precise time of
each type of output from the program-change detector 60 and stores
this data, which can be analyzed after the classification process
to determine the duration of identified programs, their position
within commercial "strings", invalid program interruptions, and
other useful information.
In the system for monitoring station-originated broadcasts 4, a
program's reference signature in most cases is formed prior to the
program's broadcast by the broadcasting station 20. Consequently,
it is possible to maintain a library of reference program
signatures in the computer 62 of each field monitor 26 and this
computer 62 can perform the classification processing on site. This
has the advantage of significantly reducing the amount of data
transmission required and, hence, operating costs. (In this case,
the central computer 28 must periodically update the library of
reference signatures stored in the memory 116.) In the network
monitoring system 2, however, this approach is not practical
because the reference signature of most programs is not known in
advance of the broadcast and the set of reference signatures
changes daily.
It should be noted that the spectral analysis performed in the
feature extraction algorithm described above might also be
accomplished in analog. The signal preconditioning module 54 could
be an array of bandpass filters, with a data-acquisition module 56
digitizing the output of each filter. The output of the
data-acquisition modules 56, representing the energy in each band
of frequencies could simply be integrated and averaged over the
sampling period to approximate the power spectrum of the program
sample and form the program's signature. Alternatively, a single
spectrum analyzer with digital output could be used in place of
both the signal preconditioning 54 and data-acquisition 56 modules.
In either configuration, since the minicomputer 62 is no longer
needed to perform the Fast Fourier Transform, it might be possible
to substitute for it one or more control microprocessors 132 at a
significant cost savings.
There are a number of algorithms that can be used in classification
processing. In the preferred embodiment, the Euclidean distance
(root-mean-square deviation) between a given broadcast feature
vector and a given reference feature vector is computer. If this
distance is less than a specified upper limit (recognition
threshold), the broadcast program is assigned the identity of the
program from which the reference feature vector was derived.
The registration unit 22 used to derive program reference
signatures has the same basic design as the field monitor 26 just
described, the principal difference being the source of the program
signal 16. Instead of the receiving antenna 50 of the field monitor
26, the source of the program signal 16 in the registration unit 22
of the network monitoring system 2 is the network feed signal
originated by network control 18. In the system for monitoring
station-originated broadcasts 4, the source is a film or videotape
playback unit. (In this case, of course, the tuner portion of the
receiver 52 is unnecessary.) The function of the program-change
detector 60 in the registration unit 22 is simply to enable the
computer 62 to measure the precise duration of each program, i.e.,
the time between detection of program-start and program-stop. This
information is stored along with the reference signature so that
any interruptions (up-cuts, down-cuts, or center-cuts) in a
broadcast can be identified. In addition, program identity and any
other necessary information for each reference signature must be
entered into the computer 62 of the registration unit 22 at the
time of registration. In the preferred embodimient, an operator
enters this data at the console of computer 62. All of this data is
then entered into the central computer 28.
As noted earlier, there are a number of possible signalling events
which can function as a cue signal. Five such signalling events
have been mentioned: an audio tone, a network logo or some other
positive signal in the active picture raster, a program change
(either a program start or stop), a temporary dropout of the VIRS
or VITS, and a signal on an otherwise unused portion of a line in
the vertical blanking interval. The cue detector 58, of course,
must be designed to detect whichever signal is being used.
In the case of an audio cue consisting of a pure tone of a certain
frequency and a certain duration, the cue signal detector 58
consists in the preferred embodiment simply of a phase locked loop
(PLL), such as the Model 567 Tone Decoder/Detector Phase Locked
Loop manufactured by the Signetics Corporation of Sunnyvale,
California. With its center frequency set to the frequency of the
cue signal and a sufficiently wide capture range to allow for
shifts in frequency due to velocity variations in broadcasting
playback equipment, the PLL locks onto the cue signal audio tone
whenever it is present in the program audio signal 17 and sends
output to the computer 62 indicating lock. By measuring the
duration of the lock output, the computer measures the duration of
the audio tone to ensure that it is consistent with that of a cue
signal, rejecting any spurious tones of the same frequency that
might occur.
FIG. 3 shows a cue detector for a positive cue in the active
picture raster according to the preferred embodiment. Such a cue
signal can be any predetermined pattern at any location within the
video signal 15, including both subliminal ancillary signals and
non-ancillary signals such as network logos. In this embodiment,
detection of such a video cue involves a separate pattern
recognition process in itself.
The composite video program signal 15 is first fed into a sync
separator 100, which separates vertical and horizontal sync pulses
102,104 from the actual program video information 106. The program
video 106 is then digitized by an analog-to-digital converter (ADC)
110 with a sample-and-hold module 108 on its input. The output of
the ADC 110 is read into register A of the correlator 112. The
correlator 112 correlates each horizontal line of a field of the
digitized video signal 106 with the corresponding line of a
"template" field stored in a memory 116, which is the reference
signature of the cue signal.
In the preferred embodiment, a one-bit ADC 110 samples the
digitized program signal at a rate of 4 MHz, generating a 256-bit
word for each horizontal line of the video signal 106. There are
commercially-available LSI (large-scale integrated) components
which can be used in the correlator 112, such as the TDC 1004J
Correlator manufactured by TRW LSI Products of Redondo Beach,
California, a 64-bit digital correlator with analog correlation
output, capable of operating at 15 MHz. The correlator 112 thus
consists of four such 64-bit TDC 1004J correlator chips in series,
the analog output of each being summed to yield the correlation
output 126 for each pair of 256-bit words.
Each word (line) of the template field is read into register B of
the correlator 112 from the template shift register 114. In
addition, in cases where the cue signal occupies only a portion of
the active picture raster, a word (line) containing "no compare"
bit positions is also read into the mask register of the correlator
112 from the mask shift register 118. The "no compare" bits cause
the correlator 112 to ignore the correlation of the corresponding
bits in registers A and B of the correlator 112, thereby allowing
the cue detector 58 to examine only a portion of the video signal
15. (If the cue signal occupies the entire picture raster the use
of the mask is unnecessary.) Both the reference field and the mask
are stored in the memory 116.
The actions of the correlator 112 and the shift registers 114,118
are strobed by a gated 4-MHz clock 122; a delay 124 allows for the
settling time required to digitize the video program information
106.
Besides the video output 106, the sync separator also outputs each
vertical sync pulse 102 and horizontal sync pulse 104. The
horizontal line counter 120 counts each horizontal sync 104; its
output is the address of the next word (line) of the reference
field and the mask to be read into the shift registers 114,118. The
counter is cleared with each vertical sync pulse 102.
The correlation output 126 of the correlator 112 is compared by the
comparator 128 to a specified threshold reference voltage 130. The
comparator 128 sends output to a microprocessor 132 only if the
correlation output exceeds this threshold. The microprocessor 132
counts the number of lines in each field which exceed the
correlation threshold 130. At each horizontal sync pulse 104, the
microprocessor 132 registers a "1" if it has received output from
the comparator 128, otherwise a "0".
At each vertical sync pulse 102, the microprocessor performs
various logic operations to determine if the cue signal was present
in the preceding frame. Primarily, it compares the number of the
appropriate lines which exceed the correlation threshold 130 to the
desired overall correlation threshold 134. If this number exceeds
the threshold, the microprocessor 132 sends a detection output 59
to the computer 62. For example, if the correlation threshold
reference 130 is 60% and the desired overall correlation threshold
134 is 80%, detection output 59 would be generated whenever 80% of
the appropriate lines in a field of the proram video signal 15
correlate with the corresponding lines of the template field more
than 60%.
The video cue detector described above is a highly versatile
design. Not only can it be used for positive cues in the active
picture raster, but it can also be used for positive or negative
cues in the vertical blanking interval since the use of the mask
can restrict examination to any portion of the video signal. It
should be noted that the only difference between positive and
negative video cue signals with respect to this design is the logic
operations used by the microprocessor 132 to identify the presence
of a cue.
Moreover, this design can also be used for the program-change
detector 60. In this case, the reference (template) field stored in
the memory 116 is that of a blank field, consisting of all zero's.
(There is no mask). If the overall correlation exceeds the
specified threshold 134, the presence of a blank field is
indicated, while two consecutive vertical sync pulses 102 without
such a correlation indicate the presence of a picture field.
FIG. 4, however, shows a simpler design for the program change
detector 60. In this embodiment, the composite video signal 15 is
fed to a comparator 128 and a sync separator 100. The function of
the comparator 128 is to determine whether the white level in the
program signal 15 exceeds a certain threshold level, indicating the
presence of picture information. This is done by comparing the
voltage of the program signal 15 to a reference voltage 138. If the
program signal 15 voltage falls below the reference voltage 138,
the white level exceeds the threshold level and the comparator 128
outputs a signal to a microprocessor 132 to indicate that picture
information is present. The sync separator 100 functions in the
same way as described above; in this case, only the vertical sync
pulse 102 is fed to the microprocessor 132. Two consecutive
vertical sync pulses 102 without an output from the comparator 128
indicates the presence of a blank field.
In either design of the program-change detector 60, the
microprocessor 132 sends a program-stop output to the computer 62
when it detects a field with picture information followed by some
number of blank fields. In the preferred embodiment, a transition
between programs is defined as a minimum of four consecutive blank
fields. (This is to allow for imperfect tape edits within
programs). A program-start output is generated when the required
number of blank fields is followed by a field containing picture
information.
As has been noted, the start or stop of a program can themselves be
used as the cue signal in the present invention. In this case, the
cue detector 58 and the program-change detector 60 are the same
component.
FIG. 5 shows a cue inserter 14 for a subliminal cue signal in the
active picture raster. In this case, cue insertion involves a
standard method used by broadcasters for superimposing one image
over another in the television signal.
The raw program composite video signal 7 is fed to a sync generator
140 and a special effects generator 142. The sync generator 100 can
be any standard unit which has genlock capability and which outputs
a composite sync, such as the Dynair Model SY-5990A Color Sync
Generator with the Model SY-5995A Genlock Module, manufactured by
Dynair Electronics Corporation of San Diego, California. The
special effects generator can also be any standard unit such as the
Dynair Model SE-260A. The sync generator 140 locks onto the
incoming video signal 7 and outputs vertical 102, horizontal 104,
and composite 141 sync pulses to the special effects generator 142
in precise phase with the syncronizing information of the incoming
video signal 7.
The cue signal, which is an arbitrary pattern, is produced by the
key generator 144. In the preferred embodiment, this is a device
similar to standard character generators commonly used in
broadcasting. When enabled by an operator, the key generator 144
inputs this video pattern to the special effects generator 142 for
the desired number of fields. The composite sync 141 output from
the sync generator 140 functions as the clock pulse for the key
generator 144. The special effects generator 142 combines the two
video sources by stripping out the program video information 106
contained in the raw composite video signal 7 at the appropriate
times and inserting instead the signal generated by the key
generator 144, thus superimposing the cue pattern over the original
program picture. The output of the special effects generator 142 is
the final program composite video signal 15.
FIG. 6 shows a cue inserter for a video cue signal in the vertical
blanking interval. The commercial availability of devices such as
the 1441/1461 Deleter/Inserters manufactured by devices such as the
1441/1461 Deleter/Inserters manufactured by Tektronix, Incorporated
of Beaverton, Oregon makes the design of such a cue inserter a
relatively trivial task. The raw program composite video signal 7
is simply fed through a deleter/inserter 146. The deleter/inserter
146 has three basic modes: in the "bypass" mode, it passes the
composite video signal through unchanged; in the "delete" mode, it
deletes any incoming signal from a particular scanning line; and in
the "insert" mode, it deletes any incoming signal from the line and
inserts a particular signal into the outgoing composite video. The
line affected in this process can be programmed to any line in the
vertical blanking interval. The Tektronix Model 1441 is for use
with dropouts in the VIRS, while the 1461 is for use with either
dropouts in the VITS or a positive cue signal on an otherwise
unused portion of any line in the vertical blanking interval. The
mode of operation of the deleter/inserter 146 is controlled
remotely through a 24-pin connector provided with the unit. This
connector is connected to a timer switch 148, which is controlled
by an operator and which, when enabled, switches the mode of the
deleter/inserter 146 for the desired amount of time.
For example, suppose the cue signal is a dropout of the VIRS or
VITS from the video signal for a single field. In this case, the
normal mode of the deleter/inserter 146 is "bypass" if the incoming
video 7 already contains the VIRS/VITS or "insert" if not. When the
operator decides to insert a cue signal, he enables the timer
switch 148, which switches the mode of the deleter/inserter to
"delete" for one sixtieth of a second and then back to its normal
mode. If the cue signal is a positive signal, such as a single
binary digit on a particular line in the vertical blanking interval
of a single field, the process is precisely the same as above
except that the normal mode of the deleter/inserter 146 is "delete"
and the timer switch 148 switches it's mode to "insert" for a
single field when enabled by the operator.
The output of the special effects generator 142 or the
deleter/inserter 146, being the final composite video signal 15
containing cue signals is either recorded on a videotape recorder
to produce the program master 30 or, in the case of a network
program, is fed to network control 18 to be distributed to the
network-affiliated broadcasting stations 20.
One of the important features of the present invention is that the
cue can be an ancillary audio signal which, unlike the
program-identifying ancillary signals of prior art method A,
satisfies the two fundamental requirements of a monitoring system:
reliability, and non-degradation of program quality. As noted
earlier, an audio cue has the advantage of being compatible with
all recording and broadcasting media.
The feasibility of an audio cue signal results from the reduction
of the time duration of the signal to the minimum necessary for
detection. This reduction makes it possible to increase the
audibility threshold of the signal, in effect making it more
difficult to be heard. An increase in the threshold means that the
signal can contain a greater amount of energy without being
audible, thereby improving reliability without causing
degradation.
There are two factors in this increase in audibility threshold.
First, at very brief signal durations, the threshold of a signal is
a function of both the energy it contains and its duration. Studies
of human audition have shown that audibility threshold is constant
for tones lasting from one half second to infinity, and only
sightly higher at a duration of 200 ms. However, as duration
decreases below 200 ms, audibility threshold increases
significantly. The threshold of a 20-ms tone is 10 dB higher than
that of a 200-ms tone. (Garner, W. R., "The Effect of Frequency
Spectrum on Temporal Integration of Energy in the Ear", Journal of
the Acoustical Society of America, vol. 19, page 808, 1947; and
Garner, W. R. and Miller, G. A., "The Masked Threshold of Pure
Tones as a Function of Duration", Journal of Experimental
Psychology, vol. 37, page 293, 1947). Thus, simply reducing the
time duration of a cue signal to less than 200 ms results in a
significant increase in audibility threshold.
The second factor in the increase of the audibility threshold for
the cue signal is masking. It is commonly recognized that one sound
can "drown out" another one. Masking is defined as this temporary
loss of the ear's sensitivity to one sound (the signal) due to the
simultaneous presence of another sound (the masker). Thus, by using
the program audio as a masker, it should be possible to increase
the audibility threshold of the ancillary signal, and thus its
energy.
The key to successful masking of the cue signal is its brief
duration. To insure complete masking, the signal being masked must
be of equal or shorter duration than the masker. For all programs
other than records, the only reasonable approach to masking with
the program audio is to use speech as the masker, and more
specifically to use components of speech, such as vowels and
consonants. Since the typical duration of such speech "phonemes" is
no more than 300 ms, it is clear that the cue signal must be
relatively brief if it is to be masked effectively.
Studies of masking have found that white noise is a more effective
masker than a pure tone. (Egan, J. P. and Hake, H. W., "On the
Masking Patterns of Simple Auditory Stimuli", Journal of the
Acoustical Society of America, vol. 22, page 622, 1950; and
Hawkins, J. E. and Stevens, S. S., "The Masking of Pure Tones and
Speech by White Noise", Journal of the Acoustical Society of
America, vol. 22, page 6, 1950) Furthermore, when a signal is being
masked by white noise, it has been shown that only frequencies
within a relatively narrow band centered on the signal frequency
actually contribute to the masking. This band is called the
"critical band", and its width depends upon the signal frequency:
the higher the frequency, the wider the critical bandwidth. A
continuous tone is completely masked up to the point where the
total noise energy in the critical bandwidth is equal to the signal
energy. (Fletcher, H., "Auditory Patterns", Journal of the
Acoustical Society of America, vol. 9, page 47, 1940) That is to
say, the audibility threshold of the signal is 0 dB relative to
critical bandwidth energy. If, further, the duration of the signal
is reduced to 20 ms, this threshold increases to 10 dB.
Consonants are essentially combinations of brief periods of silence
and bursts of noise, while vowels are basically combinations of
relatively pure tones. (Heinz, J. M. and Stevens, K. N., "On the
Properties of Voiceless Fricative Consonants", Journal of the
Acoustical Society of America, vol 33, page 589, 1961; and Hughes,
G. W. and Halle, M., "Spectral Properties of Fricative Consonants",
Journal of the Acoustical Society of America, vol. 28, page 303,
1956) Of the two, consonants are the better maskers for three
reasons. First, as noted above, noise is a more effective masker
than pure tones. Secondly, the spectral composition of consonants
varies less among different speakers than vowels, so consonants
will thus be more universally available as maskers. And finally,
the noise energy of consonants is distributed over a much broader
range of frequencies than vowels, which are limited to no more than
about 3 kHz. Thus, only the consonants could mask higher-frequency
cue signals, which are advantageous because a shorter time duration
is required to generate the number of cycles necessary for
detection by the phase locked loop cue detector 58. The fricative
consonants, which include the "s", "sh", and "z" sounds (plus the
affricative "ch"), are especially effective as maskers as they
usually contain greater amounts of energy than other
consonants.
In the preferred embodiment, the audio cue signal is a 5 kHz sine
wave with a duration of 20 ms. It is inserted into the program at
points where it will be masked by noise energies present in the
program audio. Ideally, noise energy within the critical bandwidth
should be fairly evenly distributed and of significant magnitude,
conditions which are likely to occur when fricatives are spoken.
The cue will be inserted at a 4 dB level relative to the average
energy in the critical bandwidth. This is still 6 dB below
audibility threshold and 10 dB above the minimum signal-to-noise
ratio (-6 dB) of the Signetics Model 567 Tone Decoder/Detector
Phase Locked Loop.
Returning now to the drawings, FIG. 7 is a block diagram of an
audio cue inserter according to the invention. The raw program
audio signal 9 is fed to a set of bandpass filters 152 and an
analog delay circuit 162. The bandpass filtering can be done by a
single filter or multiple filters. The output of each filter 152 is
digitized by an analog-to-digital converter 110 with a
sample-and-hold module 108 on its input. The purpose of the
bandpass filtering is to restrict the frequencies being digitized
to those frequencies in the critical bandwidth of the cue signal
frequencies. The critical bandwidth at 5 kHz is 300 Hz, so the
bandpass filters 152 in the preferred embodiment attentuate all
frequencies below 4.85 kHz and above 5.15 kHz. In the preferred
embodiment, a single 300-Hz bandpass filter 152 is used. The output
of the ADC 110, representing the total energy in the the critical
band, is read by a control microprocessor 132.
The microprocessor 132 performs various programmed logic operations
on the digitized signal and determines the location in the program
signal at which to insert each cue signal. These logic operations
comparing the total energy in the critical bandwidth to a specified
threshold so that the energy in the cue will always exceed a
certain minimum level. Another logic operation is to measure the
duration of the energies in the incoming frequency bands in order
to ensure that the duration of the masker is greater than the cue
signal. Finally, the microprocessor 132 compares the elapsed time
since the previous cue insertion in order to ensure minimum
separation between cues. The actions of the control microprocessor
132 and ADC 110 are strobed by the clock 122, with a delay circuit
124 to allow time for the ADC 116 to settle.
When these logic operations result in the identification of a sound
in the raw program audio signal 9 suitable for masking the cue
signal, the microprocessor 132 enables the switch 154, holding it
closed for the duration of the cue, which is 20 ms in the preferred
embodiment. When this switch 154 is closed, the output of the tone
generator 156, which is a 5 KHz sine wave in the preferred
embodiment, is fed through a variable gain amplifier 158 and enters
the adder 160. The amplification of the tone by this amplifier 158
is controled by the microprocessor 132 so that the cue signal is 4
dB relative to the total energy in the critical bandwidth of the
masker. The microprocessor 132 sets the gain level of the
programmable gain amplifier 158 equal to about 2.5 times the
average integrated value of the ADC 116 output over the entire
duration of the cue.
The delay 162 delays the program signal 9 so that the control
microprocessor 132 has sufficient time to perform all of the
various logic operations and generate the cue. Thus, the amplified
output of the tone generator initially enters the adder 160 with
the delayed program signal 9 at the time intended for cue
insertion. It should be noted that, if the source of the program
audio signal 9 is a tapedeck, as it usually will be, the function
of the delay 162 can be accomplished by using two pickup heads
instead of one. The bandpass filters 152 receive the audio signal 9
from a pickup head that is placed slightly in front of the second
head, which supplies the program signal 9 to the adder 160. The
spacial separation between the two pickup heads would create a time
separation between the two signals which would allow the
microprocessor 132 to perform its function.
The output of the adder, being the final program signal 17, is
recorded by the recorder 162 on some recording medium, which is
normally tape but can also be disc or film. This recording is the
master copy 30 of the program.
It should be noted in passing that the various configurations of a
monitoring system according to the present invention which have
been described above assume the use of present-day,
state-of-the-art solid state electronic devices in the design of
the field monitors. It is felt that this approach is optimal in
terms of economy, reliability, and speed of reporting. However, it
is also possible to envision an embodiment of the invention in
which the field monitors 26 tape record monitored broadcasts and in
which both feature extraction and classification processing are
performed by a central computer 28.
FIG. 8, for example, shows a diagram of a field monitor 26 which is
designed for tape recording broadcasts. In this configuration, the
program signal 16 output from the receiver 52 is recorded on tape
by the recorder 188. (This can be either an audio or video tape
recorder.) Actually, this is all that is absolutely necessary, for
these tape recorded broadcasts could simply be shipped directly to
the central computer 28. In this embodiment of a field monitor 26,
of course, the link 27 between the monitor 26 and the central
computer 28 is not a telecommunications link as defined above but a
physical transfer of the tapes containing the recorded
broadcasts.
Considerable advantage, however, is gained by detecting the cue
signals at the monitoring site. For example, by adding a cue
detector 58 and a control switch 190, the recorder 188 can be
switched on when a cue is detected in order to record the program
being broadcast, and then off again until the next cue is received.
Thus, only programs containing cue signals are recorded.
Alternatively, the tape recorder could record continuously and the
output of the cue detector 58 could be fed directly to the recorder
188 (dotted line) and recorded on a separate track. This way,
instead of the central computer 28 having to search the entire
broadcast signal for cue signals, the tape can be advanced forward
rapidly until the presence of a recorded cue detection output 59 on
the otherwise empty track is sensed. In both cases, the amount of
time required to process the tape recordings is significantly
reduced.
In view of the description of the preferred embodiment and the
discussion of alternative forms of this invention, it is clear that
the method and system described herein do not depend exclusively on
the addition of ancillary cue signals to broadcast program
material. Provision has been made for using normally-occurring
signalling events, such as network logos and interruptions in the
program signal which separate different broadcast programs, as an
effective means for selectively activating the feature extraction
process.
Moreover, where ancillary cue signals are used, the present
invention avoids the disadvantages that are attendant upon prior
art methods involving the transmission of coded identification
signals. By reducing the time duration of the ancillary signal to
the minimum necessary for detection of the signal's presence, the
present invention greatly reduces the chance of program degredation
resulting from the signals and significantly increases the
efficiency of utilization of scarce spectrum space.
Furthermore, in comparison to any monitoring scheme using only
computerized pattern recognition techniques without combination
with signalling events, the present invention avoids the burdensome
necessity of continuous pattern recognition processing on the
broadcast signal. This invention shows how the presence of either
ancillary or non-ancillary cue signals can be used to provide at
least four important and heretofore unvavailable functions: First,
these cues differentiate the program segments from which reference
signatures have been derived from all or most of the rest of the
broadcast signal. Secondly, the cues act as synchronizing signals,
ensuring proper registration in the sampling process so that the
same program information is always used to form a program's
signature. As a result of these advantages, the monitoring system
can ignore all portions of the broadcast signal which are not
associated with a cue, thus greatly reducing the amount of data
processing required. Thirdly, the cue signals eliminate the need
for concurrent feature extraction and classification processing,
thereby allowing much more design flexibility. Finally, cue signals
derived from the detection of blank fields in the broadcast signal
provide a novel type of signalling event which accurately marks the
start and stop of each broadcast program, thereby enabling precise
measurement of program duration.
* * * * *