On 16 Dec 2011, at 8:45 AM, Eric Smith wrote:
It would have been better (IMHO) to shift the sound
subcarrier frequency by 0.1%, and keep the scan rate the same.
Without a doubt.
None of the existing receiving equipment
(televisions) of the day had a precise enough sound demodulator that this would have made
any difference whatsoever. I told that the FCC wouldn't let them shift the sound
carrier, but I have no idea why.
I find it particularly odd given that the first NTSC committee was happy to radically
change the deviation on the audio carrier (from 75kHz to 25kHz). I've heard claims
that NTSC 1950 chose to tinker with the rate in the holy name of compatibility (i.e., that
existing B&W receivers would not have been able to properly recover audio) and that
because NTSC 1940 includes the horizontal and vertical sync information that the video
portion of the receiver was inherently more accommodating to the change. I'm
skeptical, and as a kid in the 1960s I think I would have preferred slightly poorer audio
to having to randomly tweak the vertical hold.
The result is the 0.1% shift in the scan rate, which
resulted in the need for really awkward and inconvenient stuff like drop-frame time code.
As well as borking the original genius of the 525 line number vis. the divider chain and
control of the master oscillator by reference to line frequency.
Nevertheless, I think that RCA and the second NTSC did
some of the most amazing and underappreciated engineering of the twentieth century.
Absolutely; these guys did amazing things with a relatively small number of vacuum tubes
that were subject to aging and thermal drift. Valensi's luminance-chrominance
encoding system dates to 1938 and the use of it to maintain compatibility with existing
B&W receivers was both a brilliant move and a demanding piece of engineering. While
NTSC sometime gets bashed as an inferior system because of problems due to differential
phase distortion, it's also the coding system for S-Video; since S-Video eliminates
phase distortion NTSC color encoding results in the highest picture resolution on the
horizontal axis and the highest frame rate of the three systems.
Then there's the political angle; if RCA hadn't sued to stop deployment of the CBS
system we might have all grown up with spinning color wheels :P
--
Dr. Christian Kennedy
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