What's involved in a true stereo effect?

[Karmasound]

I would have to have 2 seperate effect circuit boards. Two inputs and two outputs. Then have the phase of one of the outputs reversed, opposite of the other? How do you reverse the phase?


If you had more than one pedal like this ex. chorus & phaser, would you have a problem running them together? Phase issues? What about tremelo and univibe?

[mikeb]

IMHO, it's better to only have the phase of the effected audio reversed, not the clean audio, otherwise you'll get too much cancellation.

There are 'cookbook' opamp circuits for phase reversal in many books and on many sites on the 'net.

Mike

[MartyMart]

Many "commercial" stereo FX offer you the "wet" output and the "dry" output, such as the Boss DM3 and Ibanez BC9 chorus.
The "dry" output is normally inverted phase from the fx.
Seems like "Phase" and cancellation s could be an issue.. !

Marty.

[zachary vex]

if what you're asking is how to reverse the direction of the sweep of the phase on both boards, that's simple enough... just use an opamp voltage inverter on the output of one unit's LFO and send that signal to the contol inputs on the other board... you don't have to finish building the LFO on the second board if you don't plan on using the two halves at different speeds.  send the same audio input to both boards.

you should explore the sound of a mutron bi-phase.  they're quite rare now (even were pretty rare years ago) but if you can find one in someone's collection to listen to and test, you'll hear a pretty high-quality version of what you are envisioning, i think, plus experience a well-thought-out control panel with almost any possibility for controlling two phasers in one box.

[Paul Perry (Frostwave)]

There is no simple answer to this, because (depending on what one wants musically) different strategies are required.
To my mind, "true stereo" means two inputs, two completely separate effect circuits (though the LFO, if any, might be in common, or opposed, or something else) and two outputs. Like a 'stereo' amp, in fact.
If something was advertised as "true stereo", and wasnt like that, I'd be pretty upset.

[Karmasound]

So as long as in/out A path went to amp A and the B in/out went to amp B then there shouldn't be any phase issues?


I would have to keep the phase reversal true and consistent? What would happen if your had the stereo pedal setup right going to 2 amps and had one phaser set to 90 degrees and the other set to say 360? Would I get phase cancellations?



ZVex I thought someone had a layout of the BiPhase somewhere. Thanks for the idea i'll be trying that when my head stops melting.


:shock:  

[petemoore]

2 speakers
  in phase, both go in and out simultaneously, relative to the wave up + / down - swings.
 out of phase, one speaker goes 'in as the other goes out'...relative to the same point in a wave.
 A typical transistor gain stage inverts phase, when the input signal voltage at base swings up +, the collector swings - .
 So if you're running multiple stages and stereo, you would have to consider how many stages, and of those how many are inverting to calculate whether there are more phase inversions on one side of stereo than the other.
 ? ---> Most modern effects stay non-inverted phasing wise?
 So if you have say three transistor gain Stages in a row...that's Stage 1Out,  2 in, 3 out...of phase with the input. Two stages would invert twice...or be non-inverting.
 In the simplest terms, when speakers out of phase are run, waveform 'cancellations' occur, say in a 2x12'' cab, if one speaker is 'sucking' when the other is 'blowing' much of the air pressure activities occur just in front of the box as pressure seeks vaccum.
 In phase is what most [all?] players prefer, Sounds louder and projects better, doesn't blow yer 1 enclosure speakers. As both speakers are producing pressure waves, and the cabinet and floor [wall] are 'focusing' these waves [they cannot go through the floor and are intensified in the directions they can go easily, like ->____ foreward], the cabinets 'projection' is improved, markedly...plus the air suspension in your multispeaker cabinet will tend to make your speakers last a little [or WHOLE LOT] longer. The pressure/vaccum of the air in the cabinet as the speaker moves it is a damper [like the spring/shock on your car] and helps keep the speaker cone from overextending.
 Basically you want to be in phase for the most part, then 'mess' with it...if  you like phasers and echos and...you're 'Moving In Stereo'.
 Speakers in the same air suspension enclosure should be in phase...did I read that or just say it?

[Mark Hammer]

What gets called "stereo" can vary so much across the pedal universe.  For instance, "stereo" outputs with a single mono input signal can involve...

1) Separation of wet and dry signals in a variety of modulated or time-based effects like chorus,analog delay, flanger, phasers.  Some of these provide a buffered dry signal output and the wet/effect signal is either mixed in (if using one output jack only) or else sent to its own jack (if two are used).  In some instances, like the recent Mayer pedals in the "non-rocketship" boxes, there is a buffered dry output *always* available so that you could even have a "stereo" fuzz with distorted and nondistorted simultaneously available from the same pedal.  In other case, like my crappy Washburn SC-7 "stereo" chorus, the separate dry signal is simply an output jack hardwired to the input jack without benefit of any buffering whatsoever.  The good aspect of this category of stereo is that the two outputs do not cancel each other.  The bad aspect is that the stereo image tends to "pull" to one side.

2) Two alternate versions of the same wet and dry signals at two outputs.  The most common incarnation of this occurs when a modulated wet signal is inverted and mixed with dry for one output and left noninverted for mixing wih dry in the other output.  You can find this as far back as the old yellow MXR Stereo Chorus from the late 70's.  This produces notches where there are humps in the other channel (and vice versa).  My more recent DOD FX20 Stereo Phaser uses this trick as well, as do countless other products.  The good aspect of this is that two different sounding outputs are available to choose from, and neither "pulls" more strongly in any direction since they are both the same effect, more or less.  The down side is that if mixed in equal proportions, the two wet signals cancel each other out, such that what might sound great on headphones all but disappears when listened to from speakers at any distance.

3) Two alternate versions of the same KIND of wet signal mixed in with dry (or not) at two outputs.  For me, the old A/DA Stereo Tapped Delay was the epitome of this.  The STD used a unique bucket brigade chip that had 6 taps that could be independently assigned to each (or both) of two outputs or summing nodes.  If you whipped up the right sort of chorus sound, both output channels would be modulated at the same time in the same way, but the two chorus sounds were not necessarily the complement of each other, so they would not cancel out in stereo.  The Mutron Bi-Phase and the Castle Dual Phaser, IIRC, could also be configured for dual-independent phasers driven by a single mono source, either synced to the same LFO or two separate LFO's.  Advantages: "pull" is adjustable and configurable, and stereo is always available.  Disadvantages: costly, complex.

4) The same signal alternately available at output A or B.  The Ibanez Flying Pan is a classic and extreme example of this.  The FP is really just a marriage of a 4-stage phaser and a ping-pong with two separate LFOs.  As the phaser sweeps up and down, the ping-pong/autopanner moves the signal from left to right outputs and back again.  Advantages: the two outputs never cancel.  Disadvantages: a little too "psychedelic" for some tastes, (though greater subtlety is probably attainable with some tinkering);  "stereo-ness" is dependent on spatial "pull" to one side or the other.  Multi-tap delays of the digital and analog type can often provide a "kinder gentler" version of this by sending alternate iterations of a delayed input to the other output summing node. Some digital reverb algorithms can soften this even further by having multiple reflections distributed across the two outputs/nodes so that the sound seems to be "spread out" rather than bouncing back and forth is some obvious way. Advantages: lush, no cancellation, less "psychdelic".  Disadvantages: pricey, NOT a simple analog mod to a pedal.

There are likely more than these 4 broad classifications, but they give you some idea of how many different meanings "stereo" can have.