Simulated stereo without using time delay?

[smoguzbenjamin]

I was thinking, a while back I was wondering if it would be possible to use 2 amps, and a BBD to create simulated stereo. Since then I've learnt a lot, and by looking at a few phasers, I realized that the notches that were out-of-phase were being created by opamps.

Now I was looking at the little gem mk II. I was wondering if I could make a second channel , and delay it by about 50 ms, then feed the dry signal to one LG2 and the delayed signal to another, with gain and volume controls controlled with dual ganged pots and tone controls before the "stereo splitter". I know this is possible with a BBD chip but I don't fancy chipping out 7 euros to simulate stereo if I can use an opamp somehow...

I was wondering if it could be done... :roll:

[Mike Burgundy]

well...anything that has a noticable difference between left and right has a certain stereo feel. The delay "widens" the stereo image (or places the virtual mic further away), but that's about it. Oh wait, because of the rather large stationary phase shift  (1487 degrees at low E fundamental) it doesn't sound like a delay, but more like a stationary phaser, effectively making the sound slightly larger. You can get "stereo" by inserting a chorus in one channel and straight feeding the other, or a tremolo, or whatever. Try tinkering with one filter, comb filters on both sides, or phasers in opposite phase (um..).

[Paul Perry (Frostwave)]

http://www.g3vfp.org/files/pseudocw.gif
might be worth a try.
I have a tiny pseudo stereo box in front of me, looks like it is just a pair of filter networks, so each side has a "very bumpy" response curve, the 2 curves sum to flat.

[smoguzbenjamin]

I used my DD-2 to create a slight time delay (50ms) with one repeat, and so it's got two outputs one dry and one wet, so I had one amp that was a little later than the other, and I loved that sound. Alas I had to borrow a friends amp during band practice So he wouldn't let me take it home, lol.

I'm trying to keep the sound as clean as I can as it's going into a homebrew 8W "stereo" amp, which is why I'm pursuing the virtual stereo effect It's also why I don't really wanna process one channel with an effect...

Paul, your filter looks interesting... might try that. I'm not sure though, might be nice to have a "wideness" control to change the delay (and the place of the virtual mike), to make it nice & flexible.... Still thinking...

[Mark Hammer]

There were a bunch of pseudo-stereo chips that came out in the late 70's and early 80's that attempted to do what one would often find in those "mono electronically reprocessed for stereo" albums.

Essentially, what they did was introduce a series of complementary notches in each "channel" so that whatever copy of the input came out on the left didn't sound exactly like the right, and vice versa, but stick 'em together and you get the whole thing...more or less.

Philips/Signetics made a couple of those.  I think the SAP option that existed on some TVs before an assortment of other encoded stereo and 5.1 programming became available is also the same sort of thing.  Some of these later chips may well use a very short delay to generate the notches, where earlier chips just use filters.

In truth, what makes something sound wider than mono is not just an audible difference if you A/B'd the left and right channels, and its not just mere time delay either.  Rather it is the constantly shifting relationship between left and right that creates the impression that "there is something going on over here, and there is something else going on over there".

So, if you have one of those home theatre systems that lets you insert some delay into the rear speakers, it doesn't sound "more stereo", it justs sounds like a bigger space when you insert delay.  In the case of splitting a chorus so that dry comes out one side and wet out the other, you DO have a shifting relationship between left and right, rather than a fixed one, and the stereo illusion of two different things happening is much stronger.

The more I think of it, the more I am getting interested in a wet-panner.  This would be a circuit that pans an effect signal between left and right mixing stages.  So, there is always a dry signal present on each side, and the wet signal, if it is being swept up and down, is also doing so.  At the same time, though, the amount of wet signal injected into the right and left mixing stages is swept back and forth, conceivably in an aperiodic way by a noise-based LFO or several separate mixed-down LFOs.  This makes the "effect" more subtle, but still allows the stereoness to come through without being distracting.

[smoguzbenjamin]

That sounds cool, but I tried a CS-9 lent t me by a friend and It sounded too much like a chorus in one ear. The distortion sounds I got from the 2 amps w/ slight delay were great and I'm afraid I fell in love with that sound. It also sounded big, or at least to me...

Maybe I'll try & find an old delay on sale for 30 euro's or so Then I'll mod it to split wet & dry outputs if it hasn't got that allready... Lots of fun in the world of DIY

[puretube]

.......This makes the "effect" more subtle, but still allows the stereoness to come through without being distracting.

...sounds like the beginning of a beautiful effectiveness...


P.S.: hope to PM you soon, Mark...

[rocket]

i am using a "still" chorus (with width control set to 0) for pseudo stereo.
digital choruses work best for me (like the ibanez dcl).

[Paul Perry (Frostwave)]

It might be worth noting, that the pseudo stereo devices with a dealy chip in them, aren't really relying (AFAIK) on the delay function, rather they are mixing hte original & delayed sound, to give a bunch of nulls (like a flanger). And also mixing with an inverted input, for a complementary set for the other side.
Back then, it was worth using a very short delay BBD chip to get a bit of phase shift..
(if I'm wrong, Mark H can tell me!)

[Maneco]

Mark,i remember those philips chips...tda3810...i have a couple somewhere,and also an old "Saber Eletronica" project,brazilian magazine...Munky ,sounds familiar?


Maneco

[smoguzbenjamin]

I might just buy that CS-9 of my girlfriend's big sis She doesn't use it anymore, and if it's satisfactory that's great. Just got to see if the width goes down far enough. I can always mod it, anyway. I'll just have to make an amp with two inputs and be able to split them. Asin L/R and 1/2 but when I get a full schemmo done I'll post it on my site

Got to get Mark's Woody going first

[Marcos - Munky]

Mark,i remember those philips chips...tda3810...i have a couple somewhere,and also an old "Saber Eletronica" project,brazilian magazine...Munky ,sounds familiar?

Yeah, I know this magazine. I have a article here of a "movie sound" from another magazine, but is a lot complicated. You need a spring reverb for it too.

[smoguzbenjamin]

I have a spring reverb! It came out of a salvaged keyboard amp... Hey I think I'll pop that in my amplifier design! thanks for reminding me