Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N17/00—Diagnosis, testing or measuring for television systems or their details
  • H04N17/06—Diagnosis, testing or measuring for television systems or their details for recorders

Definitions

• the present invention relates to video recording and playback systems and, more particularly, to a method and apparatus for adjusting such systems to minimize deterioration of video signals recorded on and reproduced from a magnetic record medium.
• the deterioration is cumulative in that the deterioration resulting from each record/playback sequence through imperfect or isadjusted video record and reproduce equipment additively combines with deteriorations resulting from all previous and following sequences through the equipment. Even a few record/playback sequences of an analog video signal through such
• SUBSTITUTE SH equipment such as occurs during electronic editing processes, produce severe deterioration of the final generation of the video signal obtained.
• VTR machines In conventional analog machines for recording and reproducing video signal information on flexible magnetic tape (herein referred to as VTR machines) , it is known that multi-generation deterioration of the resulting video signal can be partially alleviated by precise adjustment of VTR machine controls determina ⁇ tive of various properties of the video signals.
• the properties of color television signals recorded and reproduced by VTR machines are influenced by VTR machine parameters such as system gain and phase, black signal level, system differential gain, system differential phase, and system frequency and transient responses.
• VTR machine parameters such as system gain and phase, black signal level, system differential gain, system differential phase, and system frequency and transient responses.
• precise adjustment of controls influencing these parameters are made during the manufacture of VTR machines, and control mechanisms are provided on the machines so that users of the machines can re-adjust some of the parameters.
• Such devices typically function to remove timing differences in received video signals by directing the signals through the adjustable time delay device and altering the delay in accordance with the timing difference between the received video signal and the stable timing reference so that the video signal is output by the device synchronously with the stable timing reference.
• TBC's and synchronizers currently used in tele ⁇ production and broadcasting applications are digital in design, and include a memory in the form of an array of digital data storage elements serving as the adjustable time delay device.
• ADC analog to digital converters
• DAC digital to analog converters
• analog video signal pro- cessing circuitry are provided to interface the storage elements to the analog video signal source and to the utilization device that is to receive the stabilized analog video signal.
• the size of the array of data storage elements is selected to provide a storage ca- pacity sufficient to enable the video signal to be de ⁇ layed for an interval that permits removal of the max ⁇ imum timing difference that occurs in the video signal with respect to the timing reference. Since new blank ⁇ ing and television synchronizing signals are commonly inserted in the video signal after it is retrieved from the memory, it is the practice not to store in the memory most of each horizontal blanking interval and
• the capacity of the memory is usually somewhat smaller than that which would be necessary to store the entirety of an interval of the video signal corresponding to the interval of maximum time delay to be provided by the memory.
• Synchronizers serve to synchronize video signals from different, unsynchronized sources. Most commonly, they are arranged to accept video signals supplied by remote sources and delay them so that they are provided synchronously with the timing reference of local sources. Some synchronizers are designed to provide a single television field or a single pair of interlaced television fields for synchronous combination with video signals provided by local sources. Field and frame synchronizers are examples of these. Other synchronizers are capable of synchronizing a continuous stream of video signals to the timing reference of local video sources. Such devices typically include a data storage element array of a size sufficient to store data from at least one and frequently two television fields.
• TBC's serve to remove timing instabilities or errors that commonly occur in video signals that, for example, are recorded on and reproduced from a magnetic medium. Generally, both continuously changing timing errors and step timing errors occur in such signals.
• TBC's having memories with large storage capacities, frequently of a size sufficient to store data from at least one television field.
• some TBC's with large storage capacities are arranged to perform also the functions of a synchronizer, and when doing so, operate in the manner generally described hereinbefore.
• TBC devices particularly those used in teleproduction and broadcasting applications, often perform additional functions in addition to ordinary time-base correction.
• the most common additional functions are: dropout compensation, system phasing control, picture enhancement, high speed tape shuttle picture composing, and advanced timing of output video signals.
• dropout compensation system phasing control
• picture enhancement high speed tape shuttle picture composing
• advanced timing of output video signals the performance of each of these functions affects the video signal and, there- fore, adjustment of the functions can enhance ultimate video signal quality obtained.
• TBC and synchronizer devices in conjunction with systems in which informa ⁇ tion is stored on video discs as well as in systems in which video information is stored on flexible magnetic tape.
• Video disc systems using one transducing head per disc recording surface having TBC and synchronizer devices have been adjusted by storing video information in a digital memory and then recirculating the stored information through the system on a non-real time basis.
• information retrieved from the video disc machine is recirculated after an interruption in time and used for the performance of adjustments of TBC and synchronizer devices.
• Such systems have been limited to non-real time recirculation of the video information because of the one transducing head per disc recording surface architecture.
• the synchronizing signals include vertical and horizontal blanking intervals, each formed of a composite of sev ⁇ eral synchronizing signals.
• the vertical blanking in ⁇ terval includes a vertical blanking level extending be ⁇ tween leading and trailing signal transition edges that determine the duration of the vertical blanking inter ⁇ val.
• On to this blanking level is impressed a number of horizontal blanking interval pulses, a number of equalization pulses, a serrated pulse interval defining a vertical sync pulse, and a burst (typically 9 to 11 cycles) of the sinusoidal chrominance subcarrier signal (color burst) following each horizontal sync pulse dur ⁇ ing about the latter one half of the vertical interval.
• Each horizontal blanking interval during the latter one half of the vertical blanking interval and the entire field of lines between consecutive vertical blanking intervals includes a horizontal blanking level extend ⁇ ing between leading and trailing signal transition edges. These edges determine the duration of the horizontal blanking interval.
• Impressed on each horizontal blanking level is a horizontal sync pulse followed by a color burst.
• One horizontal sync pulse and one color burst are provided for each horizontal line of the television signal and serve to keep the horizontal scanning and color generation synchronized.
• the vertical sync pulse is provided for each field of the television signal to keep vertical scanning syn ⁇ chronized.
• the serrations of the vertical sync pulse prevent loss of horizontal scanning synchronization.
• Equalization pulses are provided to insure proper scanning motion synchronization with the required spatial interlacing of the two fields that compose a television frame.
• SUBSTITUTE SHEET levels serve to blank the display during horizontal and vertical retraces, with the associated transition edges effecting a smooth signal change between the video information signal intervals and the blanking inter- vals.
• NTSC color television signals are organized into frames of 525 horizontal lines occurring at a frame rate of 30 Hertz. Since each frame includes two fields, each consisting of 262-1/2 horizontal lines, the field rate is 60 Hertz. The horizontal line rate is approximately 15,750 Hertz and the color subcarrier frequency is about 3.58 Megahertz.
• the frequency of the color subcarrier component is such that each horizontal line contains exactly 227-1/2 cycles of a continuous color subcarrier wave.
• horizontal lines cannot be readily inter ⁇ changed with each other without the exercise of care to maintain phase coherence in respect of the chrominance component of the color video signal. Such care also has to be exercised when using one field of a video signal in place of another.
• television signals are composites of video information signals and several synchronizing signals. More particularly, television signals are formed of lines of video infor ⁇ mation separated by intervals of horizontal and vertical synchronizing signals. In terms of raster
• the synchronizing signals organize the video information into separate horizontal lines that are uniformly distributed vertically to define fields. More particularly, the vertical sync pulses define the beginning of each field at the top of the raster, and horizontal sync pulses define the beginning of each horizontal line in the raster. The odd-numbered lines in the interlaced raster define one field, and the even-numbered lines define another field. Thus, it can be said that each frame is composed of odd and even fields of interlaced horizontal lines.
• the synchronizing signals also include color subcarrier signals. A burst signal of such subcarrier is provided for each horizontal scanning line and serves as a phase reference for color generation, or hue, in the line.
• a system in one embodiment, includes a VTR machine of the analog type having time base correction circuitry including a memory of sufficient capacity to provide a selected delay of a selected interval of a color video signal. Means are coupled to the memory for receiving the selected interval of the video signal after the delay and for recirculating it for recording and reproducing on the tape of the VTR machine. A control means is coupled to the VTR for causing the selected interval of the video signal to be recorded, reproduced and recir ⁇ culated a selected number of times. Means are coupled for receiving the recirculated video signal and respon- sively adjusting controls of the VTR machine based upon changes in recirculated signals detected by comparing different generations of the recirculated signals.
• the delay provided by the memory is selected to maintain a synchronous relationship between the chrominance component of the video signal and an independently generated stable color subcarrier reference timing signal, while permitting the interval of the color video signal to be so recorded and reproduced the selected number of times repetitively and continuously without interruption in time.
• FIGURE 1 is a pictorial view of a tape guide drum assembly for a videotape recording and playback machine of the rotary head helical scan type.
• FIGURE 2 is a schematic diagram of a section of videotape having information magnetically recorded thereon by, for example, the assembly of FIGURE 1;
• FIGURE 3 is a functional block diagram of a videotape recording and playback apparatus in a system according to the present invention.
• FIGURE 4 is a functional block diagram of a videotape recording and playback apparatus incorpora- ting a system according to the present invention.
• FIGURE 1 generally shows a cylindrical tape guide drum assembly 11 such as used in VTR machines that employ rotating heads to record and reproduce video information from flexible magnetic tape as the tape is transported in a helical path about the drum.
• drum assembly 11 includes an upper drum 13 that is rotatable about a central shaft 17 and a stationary lower drum 15 that is axially aligned with the upper drum.
• ⁇ first guide member 21 is mounted to guide magnetic tape 19 onto stationary lower drum 15, and a second guide member 23 is mounted to guide the tape off upper rotary drum 13.
• At least two electromagnetic transducing heads 27 and 29 are mounted at circumferentially spaced locations on rotary drum 13.
• trans ⁇ ducing head 27 can be understood to operate to record video information on tape 19
• transducing head 29 can be understood to operate to playback information from the tape.
• VTR's constructed to record and playback video information according to the Type C tape format standard typically include such transducing heads, and such heads are commonly operated to record and playback information simultaneously.
• tracks 31 of video information such as shown in FIGURE 2 can be magnetically recorded on tape 19 by transducing head 27. More particularly, the information tracks 31 are discrete and parallel, and are positioned at a sufficiently small angle relative to the longitudinal centerline of tape 19 that the length of each track 31 substantially exceeds the width of tape 19.
• the information recorded along tracks 31 typically is a composite television signal including video information and synchronizing information used in the control of the operation of television signal processing devices upon playback of the recorded information from the tape 19. During playback, however, the previously discussed distortions and other instabilities can appear in the reproduced video signals.
• FIGURE 3 generally shows a video system comprising a VTR machine 106 of the analog type and a TBC device 107 connected to correct time displacement errors in the video signals at the output of the VTR machine.
• a TBC device is usually provided in a stand-alone chassis, a VTR machine and a TBC device can be considered functionally integral as shown in the system in FIGURE 3.
• the TBC device 107 should be understood to include conventional analog- to-digital conversion circuitry at its input, and conventional digital-to-analog conversion circuitry at its output.
• TBC device 107 includes a memory of sufficient capacity to store, in digital form, at least one field of the video information portion of a composite television signal.
• the memory of TBC 107 can act to delay the video information played back by the VTR for an interval corresponding to the interval of video information that is repetitively recorded on and played back from tape 19. This delay provided by the memory cooperates with the simultaneous record and playback operations performed by transducing heads 27 and 29 to enable repetitive recording and playing back of the interval of composite video information continuously without interruption (i.e., in real time) for a selected number of times to obtain a desired number of generations of the interval of composite video information.
• the system in FIGURE 3 further includes one or more controls 108 for selectively adjusting elements that materially affect the signal processing circuits within VTR machine 106 and TBC device 107.
• controls 108 can include variable capacitances and resistances to control bandpass widths of filters in the signal processing circuitry.
• controls 108 usually provide adjustment of parameters such as system gain and phase, black level, system differential gain, system differential phase, and system frequency and transient responses.
• controls 108 enable adjustment of the delay interval provided by TBC 107. In digital TBCs, such adjustment is achieved by controlling the memory address generators operatively associated with the memory of the TBC.
• the system in FIGURE 3 further includes a video signal generator 113 connected to a video switch 123 via a line 115.
• Video signal generator 113 can be, for example, a video camera, another VTR machine, or a computer that is programmed to provide video information.
• signal generator 113 includes means to provide standard video test signals such as color-bar test patterns.
• Signal generator 113 also provides indicating ⁇ ignals to a counter 131 that, in the illustrated embodiment, is shown as integral to video switch 123. In practice, the indicating signals are derived from horizontal sync pulses present in the video test signals.
• Counter 131 is a conventional device that sequentially counts the indicating signals and provides an output to actuate video switch 123 whenever a preselected count number is reached.
• video switch 123 has two operating positions. In its first position, switch 123 connects video signal generator 113 to VTR machine 106 via line 125. In its second position, video switch 123 provides recirculation of video signals through VTR machine 107 by connecting line 125 to line 133 at the output of TBC device 107.
• the return routing can be provided through a direct cable, as indicated by line 133, or through a conventional routing switcher.
• a signal monitor 139 is connected to receive output signals from TBC device 107.
• the purpose of monitor 139 is to detect changes in parameters of video signal information caused by misadjustment of the system through which the video signal passes as the signal is repetitively recorded on and reproduced from the tape associated with VTR 108.
• Monitor 139 can be, for example, an oscilloscope or a voltage comparator that indicates changes in signal level caused by misadjust ents in system gain.
• This interval results in establishing a part of the signal delay through the system and is selected to achieve the desired repetitive recording and playing back of the selected interval of video test signal.
• the balance of the delay is provided by the normal signal propagation delay through the system and the selected memory delay in TBC 107.
• the system in FIGURE 3 further operates such that, after the video test signal information is played back, the signal information is transmitted to TBC device 107 for digitizing and storage in the device's memory. After a predetermined delay period in memory equal to the desired total delay less the combined delays resulting from the normal signal propagation delay through the system and circumferential separation of the record transducing head 27 and playback transducing head 29 (FIGURE 1) , the stored information is recalled from memory. the input of VTR machine 106. Upon receiving the recirculated test signal information, VTR machine 106 again records, reproduces, and re-transmits the signal information to TBC device 107.
• TBC device 107 once again digitizes and stores the transmitted signal, then recalls and recirculates the signal information after the selected delay.
• the steps involved in recirculating, recording, reproducing, and storing the video signal information can be continued for any desired number of cycles or generations.
• the video signal from TBC device 107 is transmitted to monitor 139 to display changes in the properties of the test signal information caused by the repeated recirculations.
• an interval of video information corresponding to an even number of consecutive horizontal lines taken from a composite video signal is recirculated for the selected number of times.
• the interval is selected to be either 262 or 264 horizontal lines in duration.
• this phase matching is maintained without the need to separate the chrominance component from the composite video signal after each playback of the signal and, therefore, without the need to process the separated chrominance component to adjust its phase to that of the color subcarrier reference before recirculating and recording the video signal again.
• Such processing of the chrominance component would be necessary if an interval of video information corresponding to one television field (262-1/2 horizontal lines in NTSC type television signals) , or an odd number of horizontal lines was selected for recirculation. As described hereinabove, such processing is to be avoided because each such processing degrades the video signal and because successive such processings, as would be necessary because of the several recirculations of the video signal, would multiply the degradation.
• SUBSTITUTE SHEET system of FIGURE 3 can be operated in a mode where, during signal recirculation, VTR 106 is caused to record recirculated video information.
• the result of the recording will be a videotape that carries the multiple generations of the recirculated field, with each generation being recorded separately on the videotape.
• the generations can be individually evaluated by repetitively playing back a single recorded track from the tape to obtain continuously a selected generation of the video test signal. Based upon evaluation of the information continuously played back from the tape, desired adjustments can be made manually to VTR 106 and TBC 107.
• FIGURE 4 shows a system for automatically adjusting a VTR machine 306.
• VTR machine 306 should be understood to include an integral TBC device of the type previously described having a memory of a capacity sufficient to store an interval of video information corresponding to the amount of delay required to be provided by the TBC.
• Existing TBCs having a memory capable of storing the video information portion of a composite video signal of at least one television field have sufficient capacity for this purpose.
• lines 351a and 351b carry recirculated signals from VTR machine 306 to a sample-and-hold circuit 355.
• the sample-and-hold circuit 355 includes first and second switches 359 and 361, respectively, that are connected for control by a digital logic circuit 365.
• sample-and-hold circuit 355 and the logic circuit 365 comprise means for automatically adjusting parameters and levels of video signals that are reproduced by VTR machine 306.
• digital logic circuit 365 and sample-and-hold circuit 355 of FIGURE 4 will now be described; however, it should be understood that those circuits are shown by way of example only and that alternative circuits can be provided to accomplish substantially the same functions.
• a first AND gate 367 in logic circuit 365 is connected to control first switch 359 in sample-and-hold circuit 355 and, similarly, an AND gate 371 in logic circuit 365 is connected to control second switch 361 in sample-and- hold circuit 355.
• Both AND gates 367 and 371 receive video drive signals, on line 375, that indicate occurrence of an input of video test signal information.
• the video drive signals can originate, for example, from a conventional signal generator.
• first AND gate 367 receives, via line 377, signals indicative of the occurrence of a selected recirculation cycle of video test signal information through VTR machine 306.
• second AND gate 371 receives signals on line 381 that indicate occurrence of a later selected recirculation of test signal information.
• the signal on line 377 preferably indicates the first generation of test signal information and the signal on line 381 indicates a preselected later generation of test signal information.
• first switch 359 is connected to a capacitor 383 in parallel with a first input of a differential
• the VTR machine 306 is placed in the standard edit mode and a tape is played back which has one field of video test signal information recorded on a track extending along the tape.
• the VTR machine 306 is caused to reproduce the recorded field of video test signal information and then to recirculate the signal for the desired number of recirculation cycles.
• the system is controlled to first commence the reproduction of the field of recorded video test signal with transducing head 29 and, after an interval that is less than one television field interval by an amount determined by the separation of the transducing heads 27 and 29 on the drum assembly 11 of FIGURE 1, i.e., after an interval of about two- thirds of a television field interval, to commence recording again in an adjacent track a field of video signals containing the selected even number of horizontal lines (262 in the preferred embodiment) taken from the original field of video test signal, using transducing head 27.
• a pulse is provided on line 375 with the duration of the pulse being sufficient to encompass the selected number of recirculation cycles; for example, the pulse on line 375 could persist for twenty recirculation cycles.
• a pulse is provided on line 377.
• the AND gate 367 With pulses on both lines 375 and 377, the AND gate 367 provides a logical "1" output signal which, in turn, maintains closure of switch 359 within sample-and-hold circuit 355. With switch 359 closed, the video output signals from VTR 306 appear across capacitor 383 and provides a voltage charge representative of the voltage level of the initially recirculated video signal information.
• a pulse is provided on line 381. That pulse causes the AND gate 371 to provide a logical "1" output on line 373 and, thereby, causing closure of switch 361 in sample-and-hold circuit 355. With switch 361 closed, capacitor 389 is charged to a voltage representative of the voltage level of the nth generation of the recirculated video signals. Thus, with capacitors 383 and 389 both charged as described above, dif ⁇ ferential amplifier 387 provides an output signal equal to the difference in voltage at its inputs.
• the output of differential amplifier 387 represents the difference in video system gain that occurred over a series of "n" recirculations through VTR machine 306.
• capacitor 383 can be charged with a reference voltage other than the voltage representa ⁇ tive of the first recirculatior of a video test signal information; in such an instance, the output of differential amplifier 387 would represent the difference between a property of the nth recircula- tion signal and the selected reference voltage.
• the sample-and-hold circuit 355 can be operated to evaluate the long term average of a signal parameter or to evaluate the signal parameter at a particular instant during the video test signal interval. If a long term average evaluation, for example, over the entire interval of the video test signal is of interest, each of the switches 359 and 361 are operated to remain closed for the entire playback interval of the video test signal during the particular generations from which samples are taken by the sample-and-hold circuit 355. Such operation is achieved, for example, by providing logical "1" pulses at the appropriate times on a lines 377 and 381 of a duration corresponding to the entire playback interval of the selected generation of the video test signal.
• the duration and time of occurrence of the logical "1" pulses are selected so that switches 359 and 361 are closed during the playback of the selected generations of the video test signal at the desired instant and for the desired duration to be evaluated. It will be appreciated that the duration and time of the sampling of the two generations of the video test signal will be selected according to the nature of the signal parameter evaluation desired.
• FIGURE 4 can be used to automatically adjust controls such as system gain controls in VTR machine 306 or in an associated time base corrector device.
• the output signals from amplifier 387 normally provide negative feedback to minimize changes in video signals as a result of several generations of recording and reproducing the signals through VTR machine 306.
• comparisons of video signal information values from different recirculation generations should be derived from the same video field. For example, if conditions were such that two interlaced video fields Fl and F2 forming a single raster frame of video information pass through VTR machine 306 during each recirculation cycle, it is preferred to compare the value of a property of a signal from the first generation of field Fl with a value of a property of the same signal from a later generation of field Fl, not field F2.
• the selected delay period be such that recirculated video signal information is repetitively displayed at nearly the same raster position upon successive recirculations. For this reason, the preferred delay period equals an even number of horizontal line intervals that is most nearly equal to the duration of one video field. Further to obtain meaningful comparisons between recirculated generations of video test signals, especially in the case of color video signals, it is necessary that recirculation be properly delayed after each generation to achieve proper phase synchronization with the color subcarrier reference signals.
• NTSC color video signals have a chrominance component whose phase alternates line to line by 180 * relative to the occurrence of the horizontal sync pulse. Also, because the horizontal lines of consecutive fields are timed to be spatially interlaced upon display at different vertically displaced raster positions, the chrominance component of horizontal lines consecutively displayed at a given raster position alternates in phase by 180 * . Thus, a sequence of four consecutive television fields occurs between displays at a given raster position of horizontal lines having a chrominance component of the same phase. Consequently, the recirculation of the video signal information through a delay of one television field interval would ' introduce an undesirable phase discontinuity in the chrominance component relative to the color subcarrier reference. Such discontinuity would prevent proper adjustment of the VTR and TBC in accordance with the present invention.
• the delay period through the recirculation path is made equal to an even number of horizontal lines. This assures that the chrominance phase of the lines retrieved from the TBC memory will be matched to the required phase defined by the phase of the color subcarrier reference. As previously described, this is accomplished in the preferred embodiment of the invention by providing a delay from the TBC memory so that a total delay is provided through the recirculation path corresponding to an interval of 262 lines.
• This synchronizing provision of the remaining horizontal lines of the video test signal is a result of the inherent operation of TBC's in providing horizontal lines of video signal synchronously relative to a stable horizontal reference timing signal, and in providing a number of horizontal lines corresponding to one television field interval synchronously relative to a stable vertical synchronizing reference timing signal.
• the aforementioned time displacement of the horizontal lines retrieved from the TBC memory coupled with the maintenance of horizontal and vertical signal timing stability results in the recirculated video test signal that gradually moves vertically through the display provided by a monitor. This movement occurs at the rate of one horizontal line per television field interval. Such movement does not interfere with the ability to adjust VTRs, TBCs and operatively associated devices in accordance with the present invention, because the chrominance, horizontal and vertical timing of the recirculated video test signal is maintained synchronous relative to the
• Common digital TBCs include a memory arranged to store digital representations of samples taken of analog video signals received by the TBC.
• the memory is operatively associated with a memory address generator that controls the times when and storage locations at which the digital representations are stored and retrieved in the memory.
• the memory address generator usually is organized in two parts, one for controlling the storage of digital representations in the memory and the other for controlling the retrieval of the representations from the memory.
• the operation of the memory address generator governing storage in the memory is controlled by timing signals derived from the color burst, horizontal sync and vertical sync components included in and extracted from the received video signal.
• the received video signal is stored in the TBC memory at times determined by the timing of the received video signal itself.
• the memory address generator is controlled by stable timing reference signals derived from the stable color subcarrier, horizontal sync and vertical sync reference signals that are commonly used to synchronize and control the operations of VTRs, TBCs and other operatively associated devices.
• the memory address generator is arranged in such TBCs to supply storage and retrieval memory address signals so that the retrieval of a video signal representation at a particular storage location normally occurs an interval following its storage corresponding to one-half the maximum delay the memory is capable of providing. This normal interval between storage and retrieval at a particular storage location occurs when the received video signal is properly timed relative to the stable reference signals.
• a difference from the proper timing relationship is reflected as a corresponding difference from the proper timing relationship between the timing signals derived from the received video signal and the stable timing reference signals.
• This difference results in a change in the interval between the times a storage location within the TBC's memory is selected by the memory address generator for storage of a particular video signal representation and for subsequent retrieval.
• Such change in the interval between the storage and retrieval of the video signal representations results in a change in the delay of the transmission of the video signal through the TBC that compensates for the difference in the timing of the received video signal. For example, if the video signal is received by the TBC earlier than the proper time defined by the stable timing reference signals, the storage locations within the TBC memory are accessed for storage earlier by the memory address generator.
• Most digital TBCs are arranged to store digital representations of the intervals of the composite video signal defined by consecutive horizontal line blanking intervals and often provide a short interval of line identifying data for each one or a plurality of the horizontal line intervals.
• the color burst, blanking, horizontal sync and vertical sync (together with the pre and post equalization intervals) synchronizing signal intervals contained in the received composite video signal are discarded in favor of new corresponding signals inserted in the video signal retrieved from the TBC memory.
• These new synchronizing signals are inserted in the retrieved video signal by output signal processing devices that are in operative association with TBCs.
• Such devices function to insert the new synchronizing signals into the video signals so that the sequence of horizontal lines retrieved from the TBC memory are organized into fields of video signals of the proper number of horizontal line intervals (for NTSC television signals, 262-1/2 line intervals), with the various new synchronizing signals located in the video signal at the proper times.
• Such signal processing devices function to insert the synchronizing signals according to the number of consecutive horizontal lines retrieved from the TBC memory, without regard to the particular raster line location in which a particular retrieved horizontal line appeared in the composite video signal received by the TBC. Consequently, the stored line intervals of digital representations can be retrieved in any order and any number of the stored intervals can be retrieved from the memory, and organized into field intervals of a composite video signal through the operation of output signal processing devices commonly included in digital TBCs.
• This characteristic of digital TBCs is used to advantage in the method and apparatus of the present invention to enable repetitive recording and playing back of an interval of the original video test signal corresponding to an even number of horizontal line intervals synchronously with the color subcarrier, horizontal sync and vertical sync related timing reference signals. More specifically, as previously described with the embodiments of the present invention illustrated in FIGURES 1-4, the video test signal played back by transducing head 29 and received at the input of, for example, TBC 107 is delayed from the time it was recorded by the circumferentially displaced transducing head 27 by an interval of about one-third of a television field interval.
• control 108 (FIGURE 3) associated with the memory address generator of TBC 107 is adjusted to set the cycle of storage location addresses generated for the retrieval of stored video signal digital representations so that the retrieval of the representations is changed to introduce a compensating delay that provides a total delay for the video test signal through the recirculation path corresponding to an even number, preferably, of 262 horizontal line intervals.
• the phase of the chrominance component in the recirculated composite video signal remains synchronized to that of the color subcarrier timing reference signal.
• Such adjustment is accomplished by discarding one horizontal line interval of the original video test signal. As previously discussed, this results in a gradual movement of the video test signal vertically upon the display.
• the chrominance, horizontal and vertical timing of the recirculated video test signal is maintained synchronous relative to the corresponding stable reference signal by virtue of the cooperative action of the TBC memory and operatively associated output signal processing device, no interference in the adjustment of the VTR, TBC and any other operatively associated devices in
• the vertical movement is an artifact that ordinarily does not substantially affect detection of changes in signal values or adjustments of video signal parameters.
• adjustment of video signal parameters can be readily made as long as the recirculated video signal information is properly timed with respect to horizontal synchronizing and color subcarrier synchronizing signals during recirculation.
• the time base corrector would be unnecessary and could be replaced by fixed delay of an appropriate length.
• an alternative way of providing a satisfactory delay period is to adjust the memory address generation to cause the TBC to introduce a total delay in the recirculation signal path corresponding to the duration of 264 horizontal lines.
• This is achieved by setting the cycle of storage location addresses generated for the retrieval of stored video signal digital representations so that the retrieval of the representations is delayed an additional horizontal line interval.
• the additional delay results in maintaining the phase of the chrominance component in the recirculated composite video signal synchronized to that of the color subcarrier timing reference signal.
• this is at the expense of introducing a gradual movement of the video test signal vertically downward upon its display on a monitor.
• the recirculated video information contained in the test signal is properly timed with respect to the horizontal synchronizing and color subcarrier synchronizing signals, and the video test signal is synchronized to the color subcarrier, horizontal and vertical synchronizing reference signals.
• the vertical shifting artifact does not ordinarily interfere with comparisons of signal values from generation to generation.
• Embodiments of the present invention can be arranged to adjust VTR's, TBC's and other operatively associated devices designed for PAL, SECAM and other television signal standards as well.
• television signals organized according to such other television signal standards have signal level, frequency, phase, timings and other well known properties that are different from television signals organized according to the NTSC standard.
• the required delay interval is readily determined from the properties of the television signal standard for which the VTR, TBC and other operatively associated devices are designed, and therefore need not be described in detail.
• the electronic edit control systems commonly associated with VTR's for teleproduction and broadcast applications can be operated to enable the continuous generation of any selected plurality of sequences of a number of regenerations of a video signal, with each sequence consisting of regenerations of a different video signal.
• This has advantages of making use of the existing edit control system to execute the steps of the recirculation technique carried out, for example, by the apparatus shown in FIGURES 3 and 4, and of making use of a convenient technique for performing the apparatus adjustment method of the present invention.
• an interval of a continuous color video test signal is first recorded by the VTR along a length of tape.
• This can be achieved, for example, by the use of the signal generator 113 of FIGURE 3.
• the switch 123 is positioned permanently to couple line 115 to the input line 125 to the VTR 106 for the duration required to record the interval of the continuous color video test signal.
• other typical control signals namely, a control track signal and a time code signal are also recorded along the tape synchronously with the video signals.
• the time code identifies each frame of video signals formed by two interlaced television fields by a unique address signal in units of hours, minutes, seconds and frames.
• the time code is in the form of the time and control code standard adopted by the Society of Motion Pictures and Television Engineers.
• the interval of continuous video test signal recorded on the tape can be of any length desired. Ordinarily, the length of the interval will be selected to provide continuously and without interruption in time a plurality of sequences of a selected number, typically, 20, regenerations each of the video test signal that will enable sufficient time to perform adjustments of the apparatus in accordance with present invention without interruption in time.
• each selected edit entry code specifies a particular frame at which a recirculated field is to be first recorded after its initial reproduction from the tape, and each selected edit exit code specifies a particular frame at which such recirculated field is to be last recorded.
• each pair of edit entry and exit codes define the selected number of recirculations of the video test signal, hence, regenerations of each sequence of the plurality sequences.
• Present electronic edit control systems are controllable to select either of the two interlaced fields of a frame identified by a time code signal for commencing or terminating an edit.
• the edit control system is operated to record successive sequences of recirculated video signals at locations along the tape separated by a tape length corresponding to that required to record one field. Since the aforedescribed helical scan VTR's record one field in each track along the tape, the series of edit entry and exit time codes are selected and the edit control system is controlled to respond to the edit exit code of one sequence and the edit entry code of the following sequence to interrupt the record operation of the VTR for an interval of time required by the VTR to transport the tape a distance separating adjacent recorded tracks on the tape.
• the edit control system is placed in an insert edit mode of operation.
• the edit control system controls the operatively associated VTR to replace an interval of previously recorded information with a new recording of information that is phase or time coherent with the remaining previously recorded information.
• the edit control system first controls the VTR to synchronize the transport of the tape to the desired normal record/reproduce speed and position the tape relative to the record transducing head at which the new recording is to be commenced. During this interval, the aforedescribed reproduce transducing head (29 in FIGURE 1) is operated to reproduce the previously recorded video test signal.
• the record transducing head While each field is reproduced and recirculated as the tape is transported to position the track identified for commencing the new recording at the location of the rotating transducing head, the record transducing head (27 in FIGURE 1) is disabled by the edit control system during this period. As the identified track reaches the location of the rotating transducing heads, the recorded time code signal identifying the track is reproduced by the time code transducing head of the VTR and is communicated to the edit control system. In response to the receipt of this reproduced time code signal, the edit control system enables the record transducing head to record the recirculated video test signal obtained from the last field of the video test signal reproduced by the reproduce transducing head before the identified track reaches the location of the rotating transducing heads.
• the record transducing head remains enabled by the edit control system until the track on the tape identified by the edit exit time code signal paired with the associated edit entry time code signal that commenced such insert edit operation reaches the location of the rotating record transducing head.
• the recirculated video test signal is repetitively recorded, reproduced and recirculated through the signal path defined, for example, by the VTR 106, TBC 107 and any other operatively associated devices in the recirculation path 133 (see FIGURE 3) as previously described. This results in the generation at output line 135 of the number of generations of the video test signal corresponding to the interval defined by the pair of edit entry and exit time codes.
• the corresponding time code signal recorded on the tape is reproduced by the time code transducing head of the VTR.
• This time code signal is communicated to the edit control system which responds by disabling the record transducing head, thereby, terminating the recording of the recirculated video test signal.
• the next edit entry time code of the selected series of edit time codes identifies a track recorded on the tape two track locations from the track along which was recorded the last recirculation of the previous sequence of recirculated video test signal. Therefore, the record transducing head remains disabled during the time one recorded track is scanned by the record transducing head. As will be appreciated, this corresponds to the interval of one television field. However, during this interval, the reproduce transducing head is operable to reproduce the video test signal recorded in the track and couple same to the operatively associated TBC and any other operatively associated devices for presentation, for example, to a monitor 139 (FIGURE 3) .
• the corresponding time code signal is reproduced by the time code transducing head of the VTR.
• the edit control system responds to the reproduced edit entry time code signal to again enable the record transducing head.
• the transducing head is enabled to record the recirculated video test signal obtained from the last field of the video test signal reproduced by the reproduce transducing head before the identified track reaches the location of the rotating transducing heads.
• the last field is the field of previously recorded original video test signal located in the track separating the tracks identified by the edit exit time code of the immediately previous completed recorded sequence of recirculated video test signal and by the edit entry time code of the next sequence of recirculated video test signal to be recorded.
• the recirculated video test signal is repetitively recorded, reproduced and recirculated through the signal path defined by the VTR and operatively associated devices coupled to the rotating record and reproduce transducing heads.
• the edit control system continues to control the VTR in aforedescribed manner in response to the selected series of edit codes it receives from the operator via an input included in controls 108 (FIGURE 3) , until the last of each of the sequences of recirculated video test signal defined associated pairs of edit entry and edit exit time codes is recorded on the tape.
• this results in the continuous and uninterrupted provision at the output of the VTR of the several sequences of multiple generations each of the video test signal.
• the edit exit and entry time codes defining each sequence and the delay interval provided by the TBC memory, the recirculated video signal will remain synchronized to the chrominance, horizontal and vertical timing reference signals.
• the video switch 123 of such apparatus performs the equivalent function performed by the edit control system in enabling and disabling the record transducing head 127 carried by drum assembly 11 of FIGURE 1.
• the switch 123 When the switch 123 is in the position that couples line 115 to the input line 125 to the VTR 106, it disconnects the VTR 106 from the recirculation path 133.
• Such synchronous relationship can be achieved and maintained by lengthening or shortening each horizontal line contained in the recirculated interval of video information by an amount corresponding to one-half, or odd multiple thereof, cycle of the color subcarrier signal component of the video signal.
• this is achieved by adjusting controls 108 associated with the memory address generator of the TBC to retrieve each horizontal line interval of the stored video test signal at a time that is changed relative to the horizontal reference timing signal by the aforesaid fraction of the color subcarrier signal cycle.
• the recirculated video signal moves gradually in the horizontal direction when display on a monitor.
• the recirculated video signal remains synchronous to the chrominance, horizontal and vertical reference timing signals throughout the duration of recirculation. This movement occurs at the field rate of the video test signal (60 Hertz in NTSC television signals) and is an amount corresponding to the number of multiple one-half cycles of color subcarrier signal that each horizontal line interval is adjusted.
• the VTR's, and any other operatively associated devices are adjusted by comparing two or more generations of the selected video signal interval obtained through recording and reproducing the selected interval by the VTR. By comparing such two or more generations, changes in the properties of the video signal can be accurately determined, since such changes can only result from operations performed on the video signal by the devices during the passages of the signal through the devices between the compared generations.

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• 1987
  • 1987-04-10 GB GB8726935A patent/GB2198907B/en not_active Expired - Lifetime
  • 1987-04-10 JP JP50258187A patent/JPS63503111A/ja active Granted
  • 1987-04-10 WO PCT/US1987/000823 patent/WO1987006420A1/en active Application Filing
  • 1987-04-10 DE DE19873790203 patent/DE3790203C2/de not_active Expired
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