Pulse detector for ascertaining the processing delay of a signal

A delay tracker utilizes a special code on the tracked signal in order to recognize such signal and ascertain any delays associated therewith.

This application claims priority to the provisional application 60/008,309 
filed Dec. 7, 1995. 
FIELD OF THE INVENTION 
This invention relates to a method and apparatus for accurately 
ascertaining the processing delay of a signal. It is particularly useful 
for synchronizing a multiplicity of signals, some of which may have passed 
through processing (including transmission systems) having delays, in 
order to resynchronize the signals at a known point in time. 
BACKGROUND OF THE INVENTION 
A problem exists in many systems when the various primary and related 
signals are processed (including by transmission and by storage, either 
direct or indirect, within a facility and/or to/from a facility). Examples 
include video systems wherein there are many video and/or audio signal 
sources from television cameras, tape recorders, direct feeds, remote 
feeds from microwave and satellite, not to mention what might occur to the 
signal--noise reduction, synchronizers, transcoders, switching facilities, 
obscenity drop circuits, etc. 
The invention is specifically usable in respect to television signals and 
will be described with such signals for a preferred embodiment. For 
example, a problem exists in many television facilities when the various 
video and audio signals are processed within the station (or from facility 
to facility for that matter). There are also many video signal sources; 
from television cameras, video tape recorders, remote feeds from microwave 
and satellite, together with signal manipulations such as noise reduction, 
etc. There are also many audio signal sources; from microphones, tape 
recorders, remote feeds, etc. subject to their own similar processing. 
Television facilities utilize routing switchers in order that the video and 
audio from any source may be connected to the input of any video or audio 
device respectively, with the outputs of those devices also being 
connected to the router so that the video and audio can be connected to 
the input of any other instrument. The video and audio may, and frequently 
do, take entirely different paths having entirely different delays. These 
paths can include many forms of active and/or passive delays. 
It is not uncommon to have a 64 by 64 matrix for each of the auxiliary and 
video signals. The output signal is frequently changed in delay by 
selection of different signal processing paths and selection of different 
ones of the input signals to be output. These router systems give 
literally hundreds of possibilities for signal path combinations, with the 
paths being frequently changed to facilitate operational needs, differing 
network feeds, local feeds, differing active processing circuits, et al. 
Frequently, the video processing path involves several devices which can 
have one or more frames of delay. Many of these devices will have a 
changing delay as the mode of operation is changed by the operator, as the 
phase of the incoming video signal drifts with respect to the other video 
signals or to the systems reference, or otherwise. Examples include noise 
reduction systems, synchronizers, transcoders, drop out compensators et 
al. 
It is not unusual for the video to suffer delays ranging from near zero to 
10 frames of delay or more--i.e. .32 seconds before the signal exits the 
system. 
The audio and secondary signals on the other hand usually are passed 
through devices which have relatively little delay compared to the video 
(although delays may be present due to processing similar to the video 
outline above). Frequently there are several audio channels, for example 2 
channels of English, 2 channels of another language, a data channel and a 
control channel. However, when the video signal and the auxiliary signals 
experience relative timing variations due to the changing delays of the 
different paths, problems occur, the most commonly noticed one being lip 
sync error when the video is delayed with respect to the audio. 
Variable delay devices exist for delaying signals and it is possible at any 
point in the system to delay the earlier arriving (typically audio) 
signal(s) to match the later arriving (typically video) signal. However, 
the problem in making such corrections arises in detecting the delay of 
the later (typically video) signal which is output from the system. This 
problem is compounded because the relative delay is constantly changing: 
the delay is often instantly changed as a signal is routed through 
different processing devices, and different ones of the many input signals 
are selected to be passed to the output. 
The U.S. Pat. No. 5,202,761, Audio Synchronization Apparatus, is an attempt 
to solve some of these related problems. In this '761 patent, a pulse was 
added only in response to the video signal and then only in the vertical 
interval. It therefore would wait until the next vertical interval to add 
a pulse in the vertical interval. This would function within a certain 
given accuracy. Since all of the video inputs may be totally asynchronous 
some video signals might have their vertical interval pulse added 
immediately. However, others might have to wait nearly a whole frame to 
have their pulse added. This gives rise to an inherent one frame 
inaccuracy. Further, various devices exist which over write or remove the 
vertical interval, severely compromising the '761's performance. 
These problems are not true in the present invention. In this invention, 
the delay of the signals which pass through the systems are measured 
through the use of a delay tracker which is associated with the signal. 
This delay tracker is carried with the signal through the system so that, 
when the selected one of the possibly many input signals is output from 
the system, the presence of the delay tracker can be detected for that 
(those) signal(s) by themselves or in combination with other signals. In a 
preferred embodiment, a delay measurement circuit means receives the delay 
tracker (directly or indirectly as later set forth) and starts counting 
time. When the delay tracker is detected on the signal out of the system, 
a delay tracker detected signal is sent to the delay measurement circuit 
which then stops the time count. The time at the stop is thereby a measure 
of the delay of the signal through the system. This measure of delay can 
then subsequently used, for example to adjust the synchronization of the 
various signals or otherwise. 
Theory of Operation of the Delay Tracker System 
In order to measure the delay of the signal which passes through the 
system, a delay tracker is present associated with the signal at a known 
point of processing. This might be at any point in the processing of such 
signal. The delay tracker is carried with the signal through the system, 
so that when the selected one of the many input signals is output from the 
system, the presence of the delay tracker can be detected and recovered 
for some use. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of this present invention to provide an improved apparatus 
and method for detecting and compensating for the delays present in 
processing various signals including the transmission thereof. 
Another object of the present invention is to provide an improved apparatus 
and method for detecting the delays of signals utilizing active portions 
thereof in order to ensure that the delay tracker passes through the 
processing means. 
A further object of the invention is to use recognizable tracker pulses to 
track a signal through processing. 
An additional object of the present invention is to allow for the 
resynchronization of a plurality of signals at a known location even after 
processing. 
Another object of the present invention is to provide for a method and 
apparatus of detecting and compensating for processing delays in a 
multiplicity of signals. 
Further objects of the present invention is to provide for a method and 
apparatus usable with a wide variety of signals having differing frequency 
content including video signals, audio signals, microwave signals, X-ray 
signals, and other signals. 
Other objects and a more complete understanding of the invention may be had 
by referring to the following description and drawings in which:

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
The delay tracker system includes a combiner 10, a tracker pulse generator 
20, a processing means 30, a tracker pulse detector 40, a delay 
determination circuit 50 and a use 60 for the delay established through 
use of the tracker pulse (FIGS. 1 and 2). 
A combiner 10 serves to associate the tracker pulse from the tracker pulse 
generator 20 with an input signal 11. The input signal may be any type of 
signal, whether amplitude, frequency, phase, digitally coded, or otherwise 
existent. This signal 11 includes video signals, audio signals, microwave 
signals, x-ray signals, digitalized signals (whether by amplitude, width, 
or other coding technique), and other types of signals having desired 
information thereon (including timing information). The signals may be 
single, related multiple signals, unrelated multiple signals, or any 
combination thereof including series and parallel forms. Further, this 
signal can be acquired for use and used with the invention at any point 
during its creation, subsequent processing, or usage including separate 
intermediate stages thereof. For clarity, the signal 11 will be discussed 
primarily as a video signal. It is to be understood, however, that this 
terminology includes any type of signal which contains information about 
which it is at some time in the signals life appropriate to measure or 
determine a delay. 
The tracker pulse generator 20 is designed to develop a tracker pulse for 
the system. While called a pulse for clarity, it may actually be any type 
of signal, for example code, frequency, burst or alteration of the signal 
11, as will be described in more detail below. Further, the tracker pulse 
could be a coding or artifact placed on the signal by already existent 
equipment, again as will be described in more detail below. This tracker 
pulse is generated in recognition with the type of signal together with 
the processing which will or is expected to occur thereon. For example, 
with a NTSC video transmission system, the tracker pulse could be an 
amplitude modulated pulse engrafted onto the luminous portion of the 
signal. With a digital system, the tracker pulse may be one or more extra 
bit(s) or byte(s) engrafted onto the string of digital coding as 
appropriate for the type of coding. It is preferred that the tracker pulse 
be invisible or imperceptible to the ultimate use to which the signal will 
eventually be applied. As later described, this can be provided through 
subsequent processing as well as careful design. Note that while an added 
pulse 21 from the generator 20 is preferred, certain parameters, 
characteristics or ancillary signals (herein called artifacts) already 
present in known signals could be utilized as tracker pulses 21. For 
example, with video signals having a time code expressed thereon, this 
code could be utilized as the tracker pulse. To utilize the certain 
artifacts present in the input signal 11, the artifacts would be 
recognized and isolated at the location of the combiner 10, with the 
recognized artifacts then being passed to the pulse detector in order that 
the pulse detector measure the distance in time between the arrival of the 
artifacts--in specific, that passing through the processing means 30 from 
that which is otherwise being passed to the pulse detector. This can be 
directly (line 22 in FIGS. 1 and 2) or indirectly (as signal 121 on signal 
11b in FIG. 2). Further note that a known clocking circuit can also be 
utilized to provide coding for the tracker pulse 21, thus eliminating the 
need for two tracker pulse paths to the delay determination circuit. For 
example, if The National Bureau of Standards time signal was utilized for 
coding, it would only be necessary for the signal(s) being tracked to 
carry the tracker pulse: the N.B.S. time signal could be separately and 
directly acquired at the delay determination circuit later described (as 
via box 23 in FIG. 2). This would preferably be utilized for non-archival 
delay tracking of individual signals. (If multiple signals were being 
processed, the delay determination circuit could subtract one count and/or 
time code from another count and/or time code to process same, thus 
effectively ignoring any common delays--even if measured in years). A 
specialized system wide coding or timing source would have the same result 
for such a system, albeit not as universal. 
The delay tracker system is designed to be used with a processing means 30 
which preferably has a known maximum delay. The reason this is important 
is that it is preferred that the tracker pulse be generated at a rate 
compatible with the maximum delay in the system. If greater accuracy is 
desired, the tracker pulse generator 20 would produce or use a 
multiplicity of distinct tracker pulses at a faster rate. Since the 
multiplicity of pulses are distinct in coding, location, or other 
ascertainable attribute, they can be separately tracked, thus 
significantly reducing the apparent effective time between tracker pulses. 
This would allow a single signal to be tracked with a great precision. 
This would also allow for multiple signals to be separately tracked 
through a single system. It would also allow a signal with unknown delay 
to be tracked by using the next recognizable tracker code at the pulse 
detector before resetting. Note that the tracker pulse generator 20 can be 
separate for each signal which is passed through the system (FIG. 1), or a 
single tracker pulse generator 20 can be utilized for a number of 
differing signals. 
The combiner 10 associates the tracker pulse 21 with the incoming signal 
11. While this pulse 21 could be at any location in the incoming signal 
61, it is preferred that this combiner 10 place the tracker pulse 21 at a 
location where it is unobtrusive, invisible or imperceptible. This can be 
passive (for example, placing a video tracker pulse into the overscan area 
of a NTSC television signal) or active (using an otherwise visible single 
point on an image, preferably displaced from the central area, perhaps 
with a subsequent drop out compensator or averaging mechanism to 
effectively remove the artifacts from the pulse at a downstream location). 
Note that individual types of delay tracker combiners can be designed for 
each type of signal which is being used, for example analog or digital (as 
appropriate) versions of NTSC, , component, composite, compressed, 
serial, parallel, time sequential, etc. since in many systems multiple 
forms of signals are used and transcoded from one form to another. 
The combiner 10 associates the tracker pulse(s) 21 at a known location or 
position in the signal 11. As this point can be accurately determined for 
use later in the processing system the pulse 21 can be subsequently 
detected. Note that it is preferred that the combiner 10 add the tracker 
pulse 21 in an active portion of the incoming video signal. This would 
allow the vertical and horizontal intervals to be utilized for other 
functions and/or allow transcoding and other modifications to the nature 
of the signal. Again, if the tracker pulse was an artifact, time, frame 
count or other attribute already present on the signal, this information 
would be developed by the user for recognition by the combiner 10, with 
this information being passed to the remaining circuits (for example by 
line 22 in FIG. 1 or 121 in FIG. 2) as appropriate for use as a 
recognizable tracker pulse. 
In the delay tracker system it is desired to add the delay tracker signal 
at some invisible or unobtrusive part of the video signal or data stream 
carrying the image. Vertical blanking or other non-image area may be used. 
However in some systems vertical blanking or various non-image data is 
stripped off which would cause the delay tracker signal therein to be 
lost. In these systems, the delay tracker signal would preferably be 
placed in the active image area of the video signal, for example in one of 
the extreme corners. Since virtually all television receivers are 
overscanned, the added delay tracker would not be visible to the home 
viewer. Furthermore, if the delay tracker signal is placed in the active 
video area, then as the video signal is converted from one form or format 
to another, for example from to NTSC and vice versa, the delay tracker 
signal will be preserved as part of the image. 
If multiple tracker pulses were to be utilized with a single input signal, 
it is preferred that the tracker pulses 21 be located at distinct 
locations on such signal or have such distinct attributes that they can be 
accurately, separately be recognized by the later described pulse 
detection circuit. For example, if one were to track four analog audio 
signals with a single video signal, the tracker pulses could be put in a) 
the four various quadrants of the video signal, b) one in the active 
picture, one in the overscan, one in the horizontal sync period and one in 
the chrominance, or c) otherwise as desired to track the four analog 
signals in respect to the video signal. Note, in this respect, that since 
there is relatively little delay in the audio signals, it would also be 
possible to use a single tracker pulse for all four audio signals. As an 
additional example, if a time code on a video signal was to be used as an 
tracker pulse, differing time codes could be used as the tracker pulses 
for the four audio signals respectively--thus allowing the delay of the 
video signal to be separately compensated for in respect to each of the 
four audio signals. 
The signal 12 output from the combiner 10 is subject to subsequent 
processing 30, which processing may occasion a delay to the signal. As 
previously set forth, it is preferred that the expected maximum of this 
delay be known in order to allow for the pulse generator 20 to insert 
tracker pulses 21 at a rate slower than the maximum delay in the system. 
Note, however, that if the maximum delay is difficult or not able to be 
accurately ascertained, the system could utilize a multiplicity of ever 
more widely separated recognizable, distinct tracker pulses, at least one 
of which has a delay longer than the practical theoretical delay for any 
type of processing system. The later described pulse detector 40 would, 
once the delay had been determined, preferably reset (i.e. ignore the 
trailing pulses 21 of the same multiplicity or begin processing anew with 
that pulse). These distinct tracker pulses 21 can also be used in 
aggregate to more closely track the delay in the system, by using 
differing distinct tracker pulses to measure the delay within the maximum 
delay in the system or by using again a multiplicity of tracker pulses 
like a venier to ascertain delay. Further, in certain systems, the tracker 
pulse 21 might have to be refreshed at an intermediate point. For example 
in a digitally encoded audio signal subject to error correction, there is 
a theoretical limit that the pulses cannot vary by more than one half of 
the clock rate. The reason for this is that, under this circumstance, an 
error correction circuitry could wipe out the signal. With this knowledge, 
it would be possible to incorporate an intermediate pulse detector system 
with the error correction circuitry in order to ensure that a fresh 
tracker pulse is always present on an audio signal. 
The processing system 30 typically adds a delay to one or more signals in 
the system, delays that can differ between signals. This processing system 
30 can be transmission, record/playback, store/reproduce, transcoding, 
synchronization, noise reduction or any other sort of action which is 
taken on the signal 12. Some of these events might occur relatively 
simultaneously (multiple sound rooms for a single live radio 
broadcast)--while some might occur over a significant period of time (the 
archival presentation of video tapes with voice over audio). However, as 
long as the tracker pulse 21 is located on the signal 12, the amount of 
delay will be able to accurately determined no matter what the processing. 
Subsequent to processing, the now delayed signal 13 is present in the 
system. This signal 13 may be present after all final processing, or may 
be intermediate to a series of processing steps. 
The signal 13 is interconnected to a pulse detector 40, which pulse 
detector 40 serves to recognize the tracker pulse 21 which is on the 
delayed signal 13. The pulse detector 40 is designed to recognize the 
particular type of tracker pulse 21 which is present on such signal 13. In 
the case of multiple tracker pulses, the pulse detector 40 would either 
recognize its own pertinent tracker pulse 21 while ignoring other tracker 
pulses that may be present on the signal or, in the case of multiple 
tracker pulses for a single signal, would react to the multiple tracker 
pulses even if these tracker pulses 21 are distinct as previously set 
forth. Note that if certain artifacts or characteristics already present 
in the signal are used as an tracker pulse, additional processing could be 
necessary to interpret such artifacts for recognition. For example, to 
convert a known frame number of a film to a specific time. 
Once the tracker pulse has been detected, the detector output 41 is used 
(FIG. 1). This use could be modifying the main signal containing the 
tracker pulse in some manner (such as repeating or dropping video frames 
or altering the relative processing delay to compensate for the delay), by 
modifying another signal (such as delaying an audio track to synchronize 
it with a video track) or otherwise as desired. 
In the preferred embodiment shown, the detector output 41 is passed to a 
delay determination circuit 50 (FIG. 2). Also input into the delay 
determination circuit 50 is a further signal having a relationship to the 
tracker pulse 21, which further signal has something with a previously 
predetermined and thus ascertainable known relationship with the signal 11 
which was subject to processing. If the tracker pulse 21 is coded with 
certain specific information--for example, the specific point of a 
specific line of a television screen or a SMPTE time code--it is only 
necessary that the further signal contain the something reflecting the 
same relative information. Since the further signal would arrive at the 
delay determination circuit 50 prior to the tracker pulse output signal 13 
(the reason being the slower than the maximum delay) the delay 
determination circuit 50 can then compare the timing of the output signal 
13 to the further signal in order to ascertain relative delay caused by 
the processing system 30. 
This signal may take many forms. Examples include the direct passage of an 
tracker pulse to the delay determination circuit 50, the passage of an 
tracker pulse on a second signal, the acquisition of tracker pulse 
information from a second source, or otherwise. 
In respect to the direct passage of an tracker pulse, this would occasion 
an interconnection between the pulse generator to the delay determination 
circuit 50 (line 22 in FIG. 2). This would, for example, be appropriate 
for tracking a single signal through processing, with or without 
subsequent manipulation of such signal. 
In respect to the passage of an tracker pulse on a second signal if 
desired, in addition or instead of tracker pulse coding, the tracker pulse 
generator 20 could send a secondary tracker pulse 121 to a secondary 
combiner 10b on the secondary signal 11b (FIG. 2). Under these 
circumstances, the delay determination circuit 50 would compare coded 
tracker pulses from two detectors 40, 40b in order to ascertain the 
relative delay between the signals 13 and 13b. This would, for example, be 
appropriate for delaying the faster signal (13b in FIG. 2) by a delay in 
order to synchronize the two signals 13, 13b. 
Note that when two signals are known to be tracked for a significant length 
of time, encoding the tracker pulse 21 with its data on the associated 
second signal would provide for a higher degree of accuracy than merely 
passing the tracker pulse 21 directly to the delay determination circuit. 
The reason for this is that the associated signal could itself be 
subjected to some minor processing delays, processing delays which would 
not be present if the tracker pulse was passed directly to the delay 
determination circuit. An example of this would be the audio of a 
television circuit being run through its own noise reduction processing 
circuit prior to being reassociated with the processed video signal. 
In respect to acquisition of an tracker pulse from a secondary source, this 
would result from the use of an tracker pulse coding based on a large 
scale technique. Examples would include the U.S. Government N.B.S. time 
clock (a recognized standard worldwide) or a systems own main clock. Under 
these circumstances, this information could be taken separately, directly 
from the secondary source 23 for both the tracker pulse 20 and the delay 
determination circuit 50 (shown FIG. 2). By using such a coding system, it 
is not necessary to pass the tracker pulse directly (line 22), or 
indirectly (line 121) past the processing system 30--the information is 
separately acquirable. This would, for example, be appropriate for 
measuring delays over vast processing networks or within a particular 
networks own distribution system. 
In certain instances, the determination of the delay could be an end in 
itself. For example, the delay can be used as a measure of quality or 
efficiency of processing 30. More typically however, the amount of delay 
once developed is utilized in some sort of use 60. This could include 
providing a readout of the relative delay, resynchronizing the signals by 
delaying a secondary signal 11B, further processing a delayed signal 13 or 
another third signal, or otherwise as appropriate. A typical use 60 for 
the invention would be to provide a delay 70 in a signal path, preferably 
a faster secondary signal 13b path, such that the delay determination 
circuit 50 controls the delay 70 (shown in dotted lines in FIG. 2) in 
order to provide a known relationship between the two signals 13 and 113b 
at this particular point in the system. A good method of resynchronizing 
signals is set forth in my co-pending Application 08/486,000 Improved 
Program Viewing Apparatus, the contents of which are included by 
reference. 
If the tracker pulse 21 was present on the delayed signal 13 in a form 
which would be perceived and/or compromise the ultimate use of the signal 
13, an optional concealer circuit 80 could be utilized intermediate the 
pulse detector 40 and the output signal 113A. This concealer 80 would 
remove or otherwise reduce the negative effects of tracker pulse 21. An 
example would be with an error control circuit. 
This circuit replaces the delay tracker signal with a video signal which is 
taken from the preceding line of video or other suitable video as is well 
known. This replacement may be performed with a standard Dropout 
Compensator (DOC). The DOC receives a signal indicating the position and 
occurrence of the delay tracker signal from the delay tracker detector to 
cause the concealment of the delay tracker signal. It could also include 
means to conceal the tracker pulse--for example, by modifying or averaging 
the pulse 21 with other surrounding signals to reduce its obtrusiveness. A 
dropout compensator would accomplish this purpose in a video circuit 
application. 
There are many modifications and permutations which can be made to the 
invention of this application without turning from its teachings. Examples 
are shown in FIGS. 3, 4, and 5. 
In FIG. 3, there are two signals 11 and 11b which are being separately 
tracked through a processing means 30, 30b. This processing means can be a 
single related processing means for both signals. Optionally, the second 
signal 11b could pass through a separate processing means 30b (as shown). 
Both signals shown have their own unique tracker pulse generators 20, 20b. 
If desired, a synchronizer 25 could be added to correlate the tracker 
pulses 21, 21b in a predictable manner. This could include full 
synchronization (although in this situation, it might be simpler to use a 
single tracker pulse generator for both signals), it could be with a known 
relationship between the two pulses 21 and 21a (for example, to compensate 
for the repetitive nature of the signals and/or the differing delays to be 
expected in the processing means 30, 30b), or otherwise. The use of the 
separate tracker pulse generators 21, 21b is preferred in that it allows 
each signal 11, 11b to be individually tracked (i.e. recognized by their 
respective pulse detectors 40, 40b). 
The two tracker pulses 21, 21b are detected by their respective pulse 
detectors 40, 40b in order to determine the appropriate delays between the 
tracked signals. This is the relationship between signal 13 and 13b, the 
relationship between signal 13b and signal 11c, and (indirectly) the 
relationship between signal 13 and signal 11c. By varying the 
interconnections of the various delay determination circuits, other 
variations are also possible. 
Once the delay is determined, it is again utilized. In FIG. 3 it is used to 
synchronize the signals 113 and 113b and to synchronize the signal 113b 
and 113c. 
An optional coordinator 45 keeps track of the respective tracker pulses 21, 
21b. This would allow the operator to keep track of the actual signals 
which are passing through the pulse detectors 40, 40b, thus providing the 
operator with information which would be otherwise not readily available. 
They would also allow an operator to synchronize signals 113 to 113b and, 
in addition, to signal 113c. Other types of multi signal synchronization 
and compensation could also be occasioned by this system. 
FIG. 4 reflects a further implementation of the invention. A tracker pulse 
generator creates the tracker pulse 21. The particular tracker pulse 21 is 
generated in response to a video signal 11, for example every 10 frames. 
Further, by using an additional circuit (a line counter 27 shown) the 
tracker pulse can be combined with the line number and timing information 
28 of the video input 11. This allows the tracker pulse 21 to be 
specifically coded with this pertinent information, thus creating a 
distinct and recognizable pulse, a delay tracker. The particular tracker 
pulse 21 shown thus includes a binary count which is incremented at the H 
rate of the reference signal. Thus there is a unique binary number for 
every line of video, and a unique number corresponding to the time when 
the signal is added to video. The combiner 10 encodes the current delay 
tracker in the video frame during which the tracker pulse 21 was received 
as previously set forth. 
After the tracker pulse 21 is combined with the input signal 11 it is 
passed through the processing means 30 in the customary manner. 
Subsequently, the delay tracker detector 40 ascertains the delay 
occasioned by the processing and, in addition, replicates the line number 
corresponding to the location of the delay tracker signal(s). This 
information is then used as appropriate to ascertain the delays in the 
system. In addition, the concealer circuit 80 removes or otherwise reduces 
negative effects the delay tracker signal so as to provide for an 
uncorrupted video output. 
In FIG. 5, a system amplifying the device of FIG. 4 is shown for one video 
channel (parts of this system are duplicated for each channel). In this 
device again a sync stripper and line counter keep track of which line of 
the video signal is currently present for use on the tracker pulse 21 (ref 
video 15 in). The particular preferred embodiment counts at the horizontal 
sync rate to develop a specific count for the tracker pulse 21. The actual 
count would vary with the anticipated maximum delay of the processing 30. 
For a typical NTSC system having a horizontal characteristic of 525 lines 
per frame, 2625 counts would allow a 10 field delay (or 12 bits of binary 
information on the tracker pulse 21). (Note this reference video can be, 
but does not have to be, one of the signals being processed). When the 
proper video location is present, the combiner 10 encodes the then current 
count in the input signal(s) at the appropriate position, for example in 
the active video, overscan, the vertical blanking or otherwise as desired. 
To allow for processing of the tracker pulse 21, it is appropriate to have 
a capacity to count greater than actually expected to allow for tolerances 
and operational speeds of the system. Note also that if an incompatible 
video or other auxiliary signal incorporated the tracker pulse appropriate 
coding suitable for the signal may be required. For example, if an analog 
audio signal would carry the tracker pulse 21, an intermittent high 
frequency carrier of 22 khz could be utilized to carry the same example 12 
bits of information with suitable accuracy. 
The tracker pulse signal 21 shown in FIG. 5 is as set forth a binary number 
which is clocked by a reference video H. In this system with multiple 
asynchronous video signals, the count is locked to a reference (in this 
case a reference video signal 15), and the same binary count is applied to 
all the delay tracker combiners 10. When the count is subsequently 
recovered from the delayed video by the detectors 40, it is subtracted 
from the current count by a delay determination circuit 50 including a 
difference calculator to give the number of video lines of delay which the 
video signal has experienced in the system. The lines of delay ascertained 
by this determinator 50 are converted to milliseconds, seconds or other 
suitable delay measure and a delay signal is output to drive a matching 
delay 101 in an auxiliary signal path, a delay such as the Pixel 
Instruments AD3100. Again, audio or other auxiliary signals could also be 
used with the system. 
It is preferred that all of the video signals carry the encoded delay 
tracker signal through the video processing system so that, no matter 
which signal is selected as the output, there will be a delay tracker on 
it allowing the delay to be measured. In the event a signal without a 
delay tracker is output, the difference calculator can be preset to output 
a default delay value, which may be preset or operator adjustable. 
This system has some real advantages. First, it is cheap to implement for 
multiple video signals. The delay tracker combiner cost is divided by $250 
per video channel. The delay detector and calculator is around $4,500. Of 
course, only one delay detector is needed per system although more can be 
used for corrections at intermediate points. 
Although the invention has been described in its preferred form with a 
certain degree of particularity, it is to be understood that numerous 
changes can be made without departing from the invention as hereinafter 
claimed.