[opendtv] Re: France bids farewell to SECAM

  • From: Olivier Houot <olho_avatar_i@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Fri, 09 Dec 2011 22:38:25 +0100

Mark Shubin wrote:
> Component is correct.
> 
> Remember, this was in the era before component equipment.  A
> component 
> vision mixer had to do everything on three paths at once.
> 

Indeed this was the era before component equipment. So it would not have
been component at the beginnings of SECAM, would it ?

Even triplicating the signal path (and i believe in that case you could
opt instead for a clever Y + sequential UV that would use only two),
would seem less complicated than using an FM demodulator, AM mixer + FM
modulator, that's why i said component would have made things simpler.
But i would be surprised that it was there at the beginning.

Off the top of my head I would situate the first all component studios
at the beginning of the eighties. Or was that for digital components
already ?

One other thing : i mentionned a loss of resolution in mixers. This was
due in fact to the use of the simpler method of luma extraction, with a
low pass filter that made the cut just below 3.9 Mhz. Resolution was
lost only in comparison to black and white studio monitors fitted with
an (anti-bell ?) filter centered on 4.3 Mhz to reject the chroma, and
fine enough to display the full 6 Mhz bandwidth of the camera signal.
But since unfortunately most consumer receivers also used that 3.9 Mhz
low pass method, the viewers would not perceive that change in
resolution.

In those mixers, chroma was extracted, but not deaccentuated, nor did it
go through a 64 µs delay line (in other words, it remained sequential
color). This reduced the number of operations needed to rebuild a
standard FM SECAM signal at the end. A < 1 µs delay on luma was needed
to compensate for chroma processing, though.

 
 
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