This option is invoked to check the integrity of time code pulses previously dubbed onto audio channel 1 (AG7350) or 2 (AG7330) by the Y option. The status of the pulses will be displayed as the tape is played until either Q or <escape> is pressed.
The computer will then display a status message, updated every second indicating whether the time codes are satisfactory, in error or not found. In addition, a history bar indicates the same information as . for OK, x for not found and e for error.
TROUBLE SHOOTING ----------------
When recording the audio pulses, the computer generates the timing of them from the frame grabber. It uses the odd field to determine the exact start and stop point of the pulse. You may notice when you are recording the pulses that there are two dots on the screen. The upper dot represents the start of the pulse, and the lower dot the end. For technical reasons the computer ignores the frame strobe coming directly from the VTR.
Now if the frame grabber is not locking on the the video sync correctly, there will often be an error in the spacing of these pulses as the frame grabber may think it receives three odd fields in a row rather than odd-even-odd. It is useful, when recording the pulses, to have them connected up to a speaker using the audio out from the VTR. When the VTR sync is being picked up correctly, you should hear a very regular click-click-click... If the frame grabber is not locking on properly, you will hear a syncupated rhythm.
In contrast, when DigImage is using the pulses, it ignores the timing of the frame grabber, and looks only at the frame strobe coming directly from the VTR. When it is playing, the frame strobe should be coming in at a constant rate, and the pulses at a lower, also constant, rate. If however the pulses are recorded incorrectly because the frame grabber had not locked on to the sync signal properly during the recording, the pulses will not be correctly spaced.
There may nevertheless be periods when the pulses are correctly spaced, between the times when they are not correct (depending on how frequently the frame grabber lost the sync signal).
When adjusting the timing to make a correction, DigImage checks the position of both the last pulse and the second last pulse. If they are both correct, then no further action is required. If they are both incorrect by the same amount, then the time is adjusted accordingly and the correction flagged. If they differ, then question marks are raised.
The existance of question marks proves that there is something wrong with the recording of the pulses. No question marks does not necessarily mean that they are correct, only that the spacing of the last two pulses was consistent. The only real way of checking the audio pulses us to use [;VVX ...]. Apart from the first half second or so, it should not pick up any errors unless there was a problem recording the pulses.