Stereo Analog Warble

[aziltz]

If this is the wrong forum, please redirect me.

I posted over at the gear page and didn't really like the choices that were suggested.  I'm looking for a stereo warble machine, but I might be seeking a new effect that isn't out there. Something very subtle, analog and warm, but in stereo.

But what does stereo mean? I think there are two major ways to think of stereo modulation in analog circuits.

1 - Mono Modulation + Stereo Panning. Diamond originally planned to do this with their newer Vibrato pedal, but later simplified things before the current production model.

B - Phase Reversal: I've read that the simple analog "stereo chorus" options available have the same dry signal in Left and Right, and the pitch/time shifted signal is out of Phase between the two. This Psychoacoustic picture, while very interesting, if mixed to mono, disappears.


I think I'm looking for something that's stereo by a different definition than both Panning and Pyschoacoustic. If you have a dry signal in both outputs, then have the pitch/time shifted signal wander between them somehow. I'm not sure how this could be achieved, but I think it might give a more interesting Tape Warble than any traditional chorus or vibrato.

The other thing I think would be interesting is oscillation that is more random than a simple sinusoidal wave. Something that wanders or drifts a bit more. Maybe what I'm looking for is a <<Stereo>> Vibrato, with a more random oscillation, where the pitch bends in one output only, and that effect pans between outputs, but the volume remains constant.


What do you guys think? I'm pretty sure there isn't anything analog out there that does this simply... Would anyone care to discuss?  Share your theories on stereo?

[chi_boy]

Anything like this?

http://www.diystompboxes.com/smfforum/index.php?topic=71168.msg596100#msg596100

[R.G.]

If this is the wrong forum, please redirect me.

It'll do for now.

I posted over at the gear page and didn't really like the choices that were suggested.  I'm looking for a stereo warble machine, but I might be seeking a new effect that isn't out there. Something very subtle, analog and warm, but in stereo.

The gear page isn't very technically deep, as I remember, so that's not a surprise.

But what does stereo mean? I think there are two major ways to think of stereo modulation in analog circuits.

"Stereo" simply means two different signals in two channels. For hifi, the "stereo" is done by mixing different signals into the two channels to place instruments psychoacoustically across the nominal sound stage. But for effects, the word has simply been degraded to mean "any differences between two channels".

1 - Mono Modulation + Stereo Panning. Diamond originally planned to do this with their newer Vibrato pedal, but later simplified things before the current production model.

Modulation? In what manner? Amplitude? Phase? Time delay? There are all kinds of modulation.
As to stereo panning, I'm guessing you're meaning repetitive auto-panning. There isn't any need for repetitive panning to do "stereo", but it does do a livelier, if somewhat cheesy different signal per channel.

B - Phase Reversal: I've read that the simple analog "stereo chorus" options available have the same dry signal in Left and Right, and the pitch/time shifted signal is out of Phase between the two. This Psychoacoustic picture, while very interesting, if mixed to mono, disappears.

Yes.
Yes.
You can actually generate some kind of different signal by any process which does something different to each output. The use of an inverted signal on chorus/flange/phase units causes different notch/peak frequencies when added to the dry signal and when subtracted from the dry signal. The reason it disappears is that the delayed signal is present as both true and inverse. Of course it disappears - it's generated in a way that's self cancelling.

I think I'm looking for something that's stereo by a different definition than both Panning and Pyschoacoustic. If you have a dry signal in both outputs, then have the pitch/time shifted signal wander between them somehow. I'm not sure how this could be achieved, but I think it might give a more interesting Tape Warble than any traditional chorus or vibrato.

Easy enough. Just split a dry signal into two mixers and a short delay. The short delay is then the input to a stereo pan which pans into another input on each mixer. If it's voltage controlled, the panning signal can be pseudorandom - irregular but vaguely repeating.

The other thing I think would be interesting is oscillation that is more random than a simple sinusoidal wave. Something that wanders or drifts a bit more. Maybe what I'm looking for is a <<Stereo>> Vibrato, with a more random oscillation, where the pitch bends in one output only, and that effect pans between outputs, but the volume remains constant.

Geofex has articles on panning, pseudorandom LFOs, VCAs, and such which can be applied to phasers, choruses and flangers. No real issue to splice the alphabet blocks together in yet another way. I think mostly this doesn't get done because there's a limited amount of space for circuits inside a pedal. This particular variant is getting toward analog synthesizer practices.

What do you guys think? I'm pretty sure there isn't anything analog out there that does this simply... Would anyone care to discuss?  Share your theories on stereo?

If there's not, it's only because no one has sat down to splice the blocks together. The concepts are easy enough and I've posted a couple of modular effects buss projects to string effects blocks together to make this kind of thing.

No magic needed, just a willingness to keep stringing blocks together.

[aziltz]

hey thanks for the great reply RG.  it seems like the block diagram is a great way to brainstorm.  I have some other projects i want to get started with first, but i think i just might tackle something like this.  Grad School is going to be a loooong 6 years...