Difference between stereo outputs and dual outputs?

[skiraly017]

Unless you had a pedal with a Balance control, or offered a left-to-right effect (pan trem), what difference would true stereo as opposed to dual outputs make? Take a chorus for example...if I had one chorus pedal with true stereo outs and one with dual outputs, both hooked up to two amps, would I be able to hear a difference between the two pedals?

[scaesic]

stereo implies different signals on both channels (panning or whatever, sometimes one is dry and one is wet).
So i guess that dual outputs implies that the same signal is coming from both outputs.

[Mark Hammer]

As you allude to, stereo is not stereo is not stereo.  My Washburn "Stereo" Chorus has two supposed output jacks, one of them simply an additional jack with a wire coming directly from the input jack.  In other words, stereo really means "through" in that pedal.

The extent to which the stereo is either audible or striking will depend on the nature of both the implementation, and the listener.  For instance, a common feature of some "stereo" modulation pedals is to provide a sum and a difference output.  One maintains phase coherence of dry and wet, and the other inverts one of those signals.  Cool.  Two chorus/phaser/flanger sounds at once!  In air, though, an inverted and noninverted copy of the wet signal will cancel if you stand at just the right spot, leaving you with LESS of an effect than you'd get from just one output.

When the stereo consists of split outputs with dry to one and wet to the other, you can get some pretty striking sounds where nothing really cancels.  The old Roland Jazz Chorus amps were really two amps in one chassis, and fed the dry signal to one power amp and speaker, and the wet to a second amp/speaker in the same cab.  People continue to view that amp as providing one of the richest sonding chorus sounds out there.  A more recent amp from SMF or somebody used a similar principle for the reverb, feeding the reverb signal to a separate amp and speaker in the same chassis, and if I'm not mistaken using a smaller speaker for the dedicated reverb channel.  reviewers in Guitar Player raved about the richness and spaciousness of the reverb.  I had a lengthy conversation with my buddy Tim the other day, who makes the CE-1 clone that was so pleasantly reviewed in Guitar Player last month.  His clone does not include separate dry/wet outs because he makes a point of using true bypass, so he had simply never used the unit in stereo.  Once he tried out (finally!) a stock CE-1 in stereo, he had an epiphany and now is completely sold on stereo, planing on a variety of products either being revised to be in stereo or designed from the ground up in stereo. 

As Doug Hammond, myself, and other users attested in one of the OT threads regarding the Tone Core Roto-Machine pedal, there are some effects that are ho-hum in mono and really only come alive in stereo.  One of the nice things about some DSP-based pedals is that they are capable of providing more nuanced and sophisticated differences between two outputs.  For instance, the Liqui-Flange sweeps across outputs, as well as within an output.  The sense of movement, if you plug into two different amps, is absolutely breathtaking.  I'm sure other DSP pedals from other companies do that to when in stereo  (At a buddy's band practice last week, I plugged one output of the Liqui-Flange to one amp, and sent the other to an Echo Park, set for tape reverse, and fed that to a separate amp.  Ever heard through-zero flanging forwards then backwards, sweeping across amps?  We practically needed a team of nurses to unplug the band's guitar player.  "Can Mark come back next practice?" )

In general, split outputs of the type skiraly017 mentioned (dry+wet) tend to produce a sensation of the sound source moving.  Depending on where you stand, it can be a litle disorienting, so watch out at gigs.  Take a listen to the Flying Pan samples over at Tone Frenzy and I think you'll see what I mean.  When the apparent movement of the sound source is too pronounced, it gets distracting.  I've told the story before, but I think the only time when I completely forgot the words to a song were when I had my guitar plugged into an amp stage right with a slow pulsing tremolo, and a second amp behind me driving a slow rotating Leslie.  It was like trying to concentrate while two different people kept tapping me on the shoulder and asking for help.

Major shifts in amplitude between two sources can be distracting and disruptive.  Sum-difference outs can evaporate in air.  This is one of the reasons why I have suggested what I like to call wet-panning, where the wet signal is alternated (smoothly) between two outputs.  There is no cancellation in air, and there is not enough of an amplitude change to be disorienting.  rather, one should get a pleasing animation to the sound, and a more spatious sense of ambience.