An idea/question -- fast switching stereo processing

[poserp]

I was thinking about the issues with stereo signals and had a rather weird idea. What if you implemented a single channel circuit, say for instance an equalizer, but at the input and output you had two very fast (i.e. mhz or ghz) dual-channel switches synchronized to the same frequency? The idea is to switch very rapidly between the channels so that both get processed by the same signal path but you, in essence, have two separate "signals". Anyways, just a thought, I'd imagine you'd have to deal with a bunch of distortion issues, among other things.

[JohnRoberts]

Good one... except that it wouldn't work...

Distortion isn't the problem. An audio frequency equalizer will just integrate the two signals together.

JR

[poserp]

What I mean is multiplexing -- the circuit between the switches operates alternately on the left and right channels, but not both at the same time, since only the left or right channel is switched onto the circuit at any particular time. You'd need to sync the input and output switches with an oscillator. I would think, though, that because you're switching the signal very quickly that you'd introduce all sorts of distortion artifacts, not to mention some of the circuit components may not be able to deal with rapid (~10^-6 sec) swings in voltage (if, for instance, the left channel is at full volume and the right channel is at zero). Any capacitors in the signal path would need to be able to charge/discharge at the rate of your switch, otherwise you'd loose the effect. Perhaps a lower switching fequency would be better -- i.e. around 400khz.

Originally Posted by JohnRoberts

Good one... except that it wouldn't work...

Distortion isn't the problem. An audio frequency equalizer will just integrate the two signals together.

JR

[JohnRoberts]

asked and answered... If you don't believe me, try it...

JR

[Stu Gutz]

Originally Posted by poserp

I was thinking about the issues with stereo signals and had a rather weird idea. What if you implemented a single channel circuit, say for instance an equalizer, but at the input and output you had two very fast (i.e. mhz or ghz) dual-channel switches synchronized to the same frequency? The idea is to switch very rapidly between the channels so that both get processed by the same signal path but you, in essence, have two separate "signals". Anyways, just a thought, I'd imagine you'd have to deal with a bunch of distortion issues, among other things.

What is the actual problem with stereo signals that you are wanting to fix?

[poserp]

John Roberts: I believe you although I'm not sure why -- is it because of latency in the circuit?

Stu Gutz: The issues are mostly economic; building a switch/oscillator circuit instead of another signal path for a stereo circuit would be much cheaper (I think, but that's just a guess based on the prices of some of the key components for the switch/oscillator circuit). But if it doesn't work, it doesn't work. I'm not on the verge of doing a parts buy or anything, but I've been thinking about building a passive EQ loosely based on some of the Helios designs floating around and that 10h inductor can be pricey. I've seen a 10h Triad inductor around for $10, but I don't know if it would be adequate for this sort of circuit. Sowter sells a 10h with a few taps for certain Neve-ish designs, but those are around $80 usd. Anyways, the basic point is one channel plus switching components would be cheaper than two channels. The other idea is that you're using components with the same values on both sides of a stereo signal, thus eliminating the issues involved with matching components in a stereo circuit.