[opendtv] Re: Analysis: Should Apple Buy Hollywood?

  • From: "John Shutt" <shuttj@xxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Mon, 27 Feb 2012 21:07:19 -0500

----- Original Message ----- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
In short, no. S-VHS tape players introduced the S-video, or Y/C interface jack. So that luminance and chrominance were separated. It was actually the first component analog interface, where the two color components were sent over the same wires.
That's why prerecorded S-VHS tapes were pretty spectacular, compared with what we had to suffer through in those days.
The reason I had one was mostly to record OTA NTSC without losing any significant image quality. With previous VHS, including HQ, recording analog TV was a real disappointment. It was not easy to get pre-recorded S-VHS at rental stores, unfortunately. 

Bert,
You make it sound as if SVHS introduced the concept of recording luminance and chrominance separately. If that was your intent, then you are mistaken. In consumer Betamax, VHS, and in the legacy consumer/industrial format U-matic that preceded them both, the process of recording onto the videotape used a technique known as "color under."
At the recorder, he incoming NTSC signal was separated into a luminance signal and a chrominance signal. The luminance signal was used to FM modulate an approximately 4 MHz carrier. The NTSC chroma was heterodyned down from it's normal 3.58 MHz carrier to a 688 KHz carrier for Betamax and U-Matic, and 629 KHz for SVHS. The two carriers were then recorded onto the videotape.
On playback, the FM luminance carrier was demodulated back to its AM signal, and the chroma carrier was heterodyned back up up to 3.58 MHz. Then the two signals were recombined into a composite NTSC signal again.
SVHS used exactly the same color under recording process, but simply improved its luminance performance by using a higher 1.6 MHz FM deviation of a 5.2 MHz luminance carrier compared to VHS's 1.0 MHz deviation of a 3.9 MHz carrier. But the basic recording process was the same for both SVHS and VHS, with separate chroma and luma being placed onto the videotape.
The advantage of the S-Video connector was to keep the 3.58 MHz chroma and baseband luminance signal separate, minimizing the number of comb filter separations required when going from the camera output to the videotape recorder input, then from the videotape recorder output to the display input. But it did not avoid the need to heterodyne the chroma carrier down to a very low frequency carrier, prior to putting it on videotape, subsequently killing chroma detail.
Betamax and U-Matic had a similar connector, but used Y/C 688 instead of Y/C 3.58. The advantage was to minimize the number of 688 KHz > 3.58 MHz and 3.58 MHz > 688 KHz heterodyning steps when dubbing tapes. 

John




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