Quote:
Originally Posted by old_tv_nut
Let's clarify the color under process. All tape mechanisms produce timing jitter that is too great for a receiver or monitor to follow the chroma frquency and phase changes. Full bandwidth systems like quad 2 inch correct the whole baseband signal including luma and chroma.
Color under systems separate the hgh frequency part of the composite signal including chroma and luma but the only correction is the phase of the chroma and burst. The jitter of the luma between 0 and 3 MHz is acceptable uncorrected. But no chroma can be allowed to go through the luma channel because it would give a total mess of corrected and uncorrected chroma.
When the signal is known to be monochrome, the color circuits can be turned off and wider bandwidth luma can be passed through the FM luminance channel. Still jittery compared to a machine with TBC, but acceptable.
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Thanks for the explanation. The colour under signsal from the tape is heterodyned back up to a stable subcarrier otherwise the receiver or monitor wouldn't be able to lock to the burst.
Quite apart from the jitter, a PAL, NTSC or SECAM colour signal has lots of energy at high video frequencies. Even if the FM recording system has enough bandwidth to record high frequency Y, it can struggle with signals that are both high frequency and high amplitude. Hence the use of high band on 2" quadruplex machines, especially in PAL with its higher frequency subcarrier.
I once worked with an A format (predecessor of C format) VTR that had a set of high band boards as an option (Ampex VR7003H). The pictures looked pretty good on high band and you got occasional colour lock. Only a few TBCs could correct a signal like this (Quantel 2001?) and I never had access to one. C format VTRS always had built-in TBCs designed to cope with this sort of signal.
Now we can look back, it's obvious that composite colour systems were a compromise. Quite a serious compromise. But at the time it was the best we could do and they were brilliant achievements.