switching at zero cross/noiseless switching

Buck Buchanan voltagecontrolled at home.com
Thu Nov 11 08:23:24 CET 1999


Hi JH,

> Excuse me, but switching noiseless with a rate of kHz cannot even work in
> theory. AM sidebands left aside, just figure that:
> How can you "wait" for the zero crossing of a signal with fundamental
> at 100Hz, when your average switching times are only 1ms apart ??
> Did I get the question wron ?

Nope, you didn't get the question wrong at all - it's just a whacky
thing to do and I didn't explain my intent well.  At low switching
frequencies (very sub audio) it is to operate as a basic 4 channel hard
panner/switch - when it get's a trigger, audio is switched to one of 4
channels (for signals jumping circularly around the room).  For this
mode of operation, I would like very quiet switching and could indeed
live with slow switch times.

But then, I want to be able to sweep the switching frequency up into the
audio range where YES, there will be all kinds of crazy sidebands and
general sonic chaos.  Here slow switch times won't work.  Will any part
of the original audio be intelligable at this point?  At what point does
the sensation of a sound moving in circles cease and it just becomes
some weird tone based on the original audio, switching speed, switching
noise, and whatever location modulation effects exist?  And then to
slowly turn it back down until once again the sensation of rotation
returns, the original audio becomes intelligable again, blah blah blah. 
Ya know that sound when you turn your linear FM up into the audio and
glide it back down to a slow sweep - sort of that effect but around the
room.

Yes this thing should make one hell of a racket once switching frequency
crosses into audio.  And yes, any zero crossing sync thing will have to
be disengaged to switch faster than the fundamental audio freq.   

I guess with all the holes in this idea I should probably be spending
more time on quad VCAs and quadratures oscillators....

Thanks JH and all for the input!

Buck



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