[BC] processing way back when

[Jim Tonne]

>> IIRC, the audio was modulated as RF to permit gain control in
>> the RF domain without thumps.
>
>
> Bob, I'm going to show some ignorance here now, what exactly are you 
> telling
> us here? I don't think I'm following your description, or I don't see what
> you're describing.

If you AGC or otherwise "change the signal level" of an ordinary AM
signal it will have thumps.  Big time.  So what they did in that unit was
to use a balanced modulator to generate DSB suppressed carrier.  Now
changing the gain (i.e., AGC activity) wouldn't cause thumps.  The DSB
signal was demodulated back to audio in a synchronous detector.  But
the thing was complex and balance in the field apparently was "iffy".

That unit was the winner of  The Fastest Limiter Ever Built contest.
(It had a zero attack time.)  Alas, as the fellows at CBS Labs and then
Bob Orban have pointed out, an AGC system that responds to 50
microsecond transients isn't very loud.  The unit controlled modulation
pretty nicely, as viewed on a scope.  It absolutely did not control
loudness, which was starting to become an issue.

- JimT