[opendtv] Re: Production Codecs

  • From: Cliff Benham <flyback1@xxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Wed, 16 Jul 2008 20:40:18 -0400

Manfredi, Albert E wrote:

IIRC, John Shutt said some time ago that there is no actual interference
problem between the chroma carrier and the audio carrier, even at 30
fps, in all NTSC receivers likely to exist today. Is this not the case?

The only case in which this might be a problem, albeit a very small one,
is when analog NTSC with a 4.5 mHz audio subcarrier is transmitted OTA, played from any consumer recorded source using a modulator or via cable

If the chroma subcarrier is 455/2 X 15750 = 3.583125 Mhz, then the beat note is no longer [~920 Khz] an odd multiple which cancels visually from line to line, and might be visible on 'some' B&W set sequipped with intercarrier sound!

At least this is the explanation given by the RCA engineers in 1953 for changing to 3.579545.454 mhz...

If true, then wouldn't ATSC offer the opportunity to begin producing
content at a true 30 or 60 fps? Since that's a legitimate option?

Seems to me that composite or S-video NTSC wouldn't care anyway, and any
laggards using the RF interface shouldn't either.

It seems from reading through all the 'official' sources including the Proceedings of the IRE Color Issue of January, 1954, that *color sets* were never affected by the 916.87 KHz beat note if 3.253125 was being used, only B&W sets!

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