True stereo?

[electroharmo]

I would like to add "true stereo" to effects boxes that i am building. What is true-stereo as far as the input and output of effects jacks? Does the circuit itself have to be designed to accommodate stereo and in and outs? thanks.

[chipaudette]

Well, I believe that "True Stereo" means that you've got two inputs and two outputs. The "Left" input goes to the "Left" output while the "Right" input goes to the "Right" output. The "true" part of "true stereo" is that the processing for the "Left" and the processing for the "Right" follow completely independent signal paths.

So, for an analog pedal to do "true stereo", you'd need to have two copies of your circuit within your pedal. One copy would effect the "Left" signal and the other copy would effect the "Right" signal. In this case, though, you might as well just build two pedals.

For a digital pedal, you'd need to have two A/D units and two D/A units and then the software in between would have to process each channel independently. But, I doubt that you're talking about building digital pedals. Has anyone here ever built a digital effects pedal? That would be an interesting and unusual project to see/hear!

Oh, and in case it's not clear, any kind of stereo setup (whether "true" or not) needs two guitar amps (or a stereo guitar amp). One amp would be to amplify the "Left" and the other amp to amplify the "Right". I ran a stereo rig for a few years...but without a roadie, I decided that it wasn't worth lugging around twice the equipment. Heavy!

Good luck,

Chip

[Mark Hammer]

"Stereo" has a great many interpretations and implementations in the pedal world. For example, I have a Washburn "stereo" chorus that has one jack on the input side and two on the output side of the pedal. In fact, the "second output" is just another jack hardwired to the input jack so that the user can plug and get the input sound out of one jack and the chorus sound out of the other. It doesn't really matter which of those two hardwired jacks you plug into; they can each function as input or "thru" jack. Is that "stereo"? Not in my books.

Stereo implementations also depend on the type of effect. For example, in modulation effects like flangers, chorus, and phasers, one often finds a "stereo" option (in addition to a normal effect+clean output) where the modulated signal comes out one jack and the clean signal comes out another. In other instances, the modulated sound is added to the clean one at one output jack, and subtracted from the clean one at the other jack. That latter form is stereo of a sort, but when those two signals are mixed to mono electronically, they cancel each other out. They cancel out in air a bit too, but that will depend on where you stand and the equivalence of the two amps/speakers.

Then there is stereo implementation for purposes of movement in the stereo field. The semi-recent Line 6 Tone Core pedals are nice for this. The Liqui-Flange and Roto-Machine (Leslie emulator) pedals have deliberate stereo movement of the basic sound, so you can do "instant Eddie Kramer" touches where a wide flange sweep also moves from one side to the other as it sweeps. A number of Tremolo pedals will also do ping-pong or panning functions where the same signal is moved back and forth. Some digital delay pedals will also do ping-pong delay, and "assign" successive repeats to alternate outputs. This is also a form of stereo.

Then there are some interesting sorts of stereo arrangements in the digital world. In corresponding with the chief programmer for the Tone Core Echo Park pedal, I learned some interesting things. Digital pedals consume much more current. This is not news to anyone. The amount of current consumed is a function of the number of clock cyles and operations required to do what needs to be done. If two inputs converge on a single DSP chip and that chip has to attend to the processing of two distinct signals, and distribute them uniquely to two different outputs, that's a LOT of clock cycles for one humble chip. So, the choice Line 6 elected to make was to do the clean processing in true stereo but pool the two inputs, do whatever delay processing was required and then assign the product to the appropriate output. The intent was to make battery-operation somewhat feasible for a modest but useful period. I can vouch that content that comes in one channel can be heard in both output channmels. One might refer to it as quasi-stereo. Clearly the two outputs are "different" but there is no distinct unique processing that provides a sort of brick wall between A and B such that it behaves like two separate delay lines in one package.

If you want to hear a sample of what happens when you take the output of one channel and reprocess it through the other channel of the same pedal, here's a sample: http://hammer.ampage.org

[GibsonLover]

'Stereo" is another word that has too many meanings like these guys pointed out. For a DIY FX box, dual mono outputs, with an option to switch phase on one side, works well. It doesn't sound like much with some effects, but for modulation type circuits you'll hear a left-right effect going on. I buy "stereo" effects when I buy new stuff because they can still be used in mono. Using a stereo head (homebrew dual-mono outputs) is a plus, as with any time or modulation effect. A 2x12 cab and stereo head is no more bulky than a mono head and 2x12 cab. Another often overlooked plus, aside from use with stereo effects, is using the dual mono amps to keep a straight signal in one side while verbing the other.

[Mark Hammer]

Keep in mind that a guitar signal is not two signals all the time the way a mixer or recorded signal is. So, in a great many instances, "stereo" consists of taking in one signal, and producing two different versions at the output for some alternate uses.

I'm one of those folks who believes that reverb and echo often (though not always) need to be perceptually distinct from the source signal in order to mentally isolate them and relegate them to background, rather than be confused with foreground. So, in service of that, it might be wiser sometimes to plug a clean guitar into an echo pedal, feed the delay out to one channel (of an amp or mixer, etc.) and feed the clean out to a distortion pedal and into another channel, instead of plugging into a distortion then into an echo pedal.

Now, the final result may well be mixed down to mono, but there is a form of dual-parallel processing that is facilitated by having dual outputs.