On Tue, 28 Jul 2020 13:21:04 +0100, John Williamson
wrote:
On 28/07/2020 12:25, None wrote:
As always, the village idiot has no idea what he's on about. NTSC audio
was FM, not AM.
In PAL land, I have a memory that the audio was FM on a sub carrier and
the video was inverse modulated AM, so interference tended to show as
black spots.
Before PAL, we used 405 lines where more signal gave a brighter spot, so
you noticed when a car drove past or someone turned a light off and the
switch sparked.
The worst thing with white-up was that the signal amplitude was
proportion to brightness, so it was impossible to find the black
level. Sync would start to roll on bright scenes and the brightness
would breathe in and out as the scene's peak brightness changed.
Once we changed to black-up, every frame had the same amplitude, black
level was always the same so you could use a simple diode clamp, and a
simple level sampler would pull the sync off. Happy days.
d
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