On Oct 8, 2014, at 6:53 PM, Dave Hogan wrote:
To record on 3/4", a composite signal with a 3.58mHz color signal superimposed onto a luminance signal was first split into it's separate chrominance and luminance signals. As 3.58Mhz is a difficult frequency to record onto slower 3/4" u-matic tape/head speeds, it is first heterodyned down to 688 kHz to record on it's separate chrominance channel. This was done to different frequencies by all helical scan recording systems. (beta, vhs and 1").
I say:
Excellent Dave, except that 1-inch (Type C) was a direct recording format, not color-under. In fact, Type C used the same FM deviation standard as high-band 2-inch quad.
Dave said:
U-matic direct color was the precursor to what also became S-video in consumer equipment, where luminance and chrominance are transmitted separately, to provide higher quality and eliminate artifacts like chroma crawl.
I add:
Technically, U-Matic Y-688 was not 'direct color', as that implies something else, but I see what you mean.
Y-688 allowed for two separate signal paths for chroma and luminance, which provided digital TBCs the option of separate time-base processing for the two signals. This resulted in the elimination of tape deck processing that normally would be added by the VTR's combining the two signals at 3.58MHz, only to have the TBC separate the two for internal processing anyway. There is always signal loss when filtering chroma and luma in order to separate the two. One will always leak into the other because the separation is not perfect. By eliminating the separation/combintion process, the quality is improved; or at least not damaged as much. This feature does not eliminate chroma crawl, though it does have the effect of improving luminance bandwidth. Dennis Degan, Video Editor-Consultant-Knowledge Bank
NBC Today Show, New York
NBC Today Show, New York
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Posted by: Dennis Degan <dennyd1@verizon.net>
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