I am no guitar expert (still learning), but i find processing guitars (or bass) in a Voyager gives me plenty of clean wah all over the neck range, and it’s easy to do variable speed phaser/flanger like sounds that are cleaner and more defined than those of a typical guitar effect pedal.
Many people have backed from processing audio signal (guitar or else) in a Voyager because they didn’t get the instant result they expected. The key here is to understand how audio signal differs from those synth Osc’s waves and what to do with them. Since the topic comes on often, i thought I’d share my abc (and d and e) of guitar processing into a sort of mini-tutorial form. Hopefully, it will be helpful to the occasional browser.
Audio signals don’t have a gate signal generated by the keyboard, so the envelope filter is out of the equation. Even worse, since the gate has to be held open, there’s not much the Volume envelope will do. Just crank up the volume sustain and that’s it. Also, the audio signal is not generated by an Oscillator, so you can’t vary it’s pitch with controllers.
So what’s left to control? Well : Filter Cut-off frequency of course. Right there is a good wah wah sound with nice analog synth overtones.
Now back again to the difference between audio and oscillator generated waves. Osc waves are very rigid in shape (even when morphed) thus predictible. Since they come out of a mono synth, there’s only one main frequency component (that of the Osc), or two or three with all osc’s turned on. Also, since they are subject to a gated envelope, their sound begs to be adjusted with just the right cut-off frequency, and resonance and EG amount (patch).
Audio signals on the other hands are not so strictly defined in nature, and carry much more frequency signal across the spectrum. The result of gradually applying a low pass filter to the signal results in dulling the sound to the point where it’s useless. A slow variation of the cut-off frequency gives deceiving results, but very fast change across the whole range will give a very good wah wah sound at any frequency.
A) Instrument level signals such as guitars are too low for audio-in, they must be boosted somewhat, to line level. For that, I use a Vox ToneLab ST set on a clean channel, and only a bit of gain and volume is used so that low strings playing will flash the audio in led in the mixer section of the Voyager. And it sounds very clean indeed : nice bottom and sparkling highs. Note that the pedal is simply used as a neutral preamp here. A boost to proper signal level can also be achieved with a standard mixer or passive box.
B) All Osc’s turned off on the Voyager, External in On (amount near max), volume sustain to max, main output level to taste. Press the EnvGate switch to On/External at this point to activate gate once (you don’t need to short a gate a the back, as is often said in other posts). Cut-off frequency set to max (12K). Clean guitar now plays. Two problems here. A good wah will require swifter knob moves than the hand will allow and then you are busy playing the guitar with both hands anyway. Here comes good old expression pedal plugged into the filter’s red jack input. The clean wah sound will come only with the full travel of the pedal, and in order to do that, it’s very important to turn the Cut-off frequency knob on the panel all the way down. Now you have the full cut-off voltage range on the pedal and you can wah your guitar all you like. Adjust resonance and filter EG amount to taste.
Very clean wah-wah sound at this point that works equally well at all frequencies, from low to high. I don’t often feel like processing already distorted sounds (from the pedal or effects processor), although there’s a world of sound possibilities there, so let’s stick to clean as we move on.
C) Now is the time to add modulation. On Mod bus 1, set source to LFO, destination to Filter, controller to mod wheel, mod wheel all the way up and amount to max. Varying LFO rate, mod wheel and amount (there are soft spots all over) will give interesting textures, that you can still combine with some pedal action. Not bad, yet it seems very modest as far as control and effect goes. We need more modulation power. That’s the next step. For now let’s forget about Mod Bus 1 and turn it’s amount to zero.
D) We are now going to use Mod Bus 2 and Osc3 as a versatile LFO to create phaser like effect on a clean guitar tone. On Mod Bus 2, set source to Osc3, destination to Filter, controller to mod wheel, mod wheel all the way up and mod bus amount to max. Also set Osc3 section : Octave to 4’, wave form to triangle and Osc3 freq switch to low. What we have a this point is a very good sweep of the filter cut-off range at the interval determined by Osc 3 (medium fast here). Adjust Octave switch up or down for large speed increments, or frequency knob (of Osc3) for fine tuning. At the other end of the line, we still have a pedal to play with and the resonance and EG amount knobs to help with tone. But much of the interesting sound combination and effects will be realized at soft spots varying mainly the mod weel and Mod Bus 2 amount in different ratio (along with OSC 3 settings). We could also play Osc3 waveforms as mod bus destination, but only the triangle wave is clean, others will leave clicking artifacts, though this might be something to explore too.
E) So : Osc3 as a LFO on Mod Bus 2 gives us very convincing and clean guitar effects. Let’s bring back the main LFO on Mod Bus 1 by giving it some amount and combine it with Osc3 on Mod Bus 2.
- By varying mainly these :
mod wheel amount
mod bus1 amount
mod bus2 amount
in all different possible positions and ratios, you will approach reverbs, phasers and flangers sounds, some quite convincing, all very clean at this point. Travel the whole range for all three controls, a bit on each at a time. There are soft spots everywhere. That’s when mod wheel amount combined with mod buss 1 and 2 amounts give nice sounding control range over the filter cut-off, paired with LFO rate and action.
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The main LFO and Osc3 section settings will controls repeat rate and such.
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Resonance (don’t go into FM) and EG amount will help with final tone You can find the growling and wobbling bass, here, as usual, with reverse EG amounts. Cut off frequency knob is kept down always : use pedal instead.
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At all time, pedal on and mod wheel off brings back full frequency clean audio, canceling both mod busses at once (handy).
It’s a pretty impressive setup at this point with only an expression pedal required. It rivals a few Moogerfoogers right on, into a matrix multiplication concerto of control voltages applied-to-filter 
I know it does keep me busy for a while.
We can increase the flexibility of the setup by adding pedal control to Resonance and EG amount in the filter section. These have no CV’s but respond to CC’s. A foot midi foot controller such as the Roland FC-300 will add two pedals that can be configured to any CC driven controller. It does not work on my OS (no midi) but it works on the Phatty or regular Voyager.
A set up with three expression pedals on : Cut-off, Resonance and EG amount (and why not add a pedal for pan while there) is a hands-off very interesting sound processing system, once you have the two LFO’s set up as above. And even when you want to adjust on the computer console, you have to concentrate on 3 controls located closeby (mod wheel and two amount knobs), with an occasional knob turn in Osc3 section.
As usual with synths, the more controllers the more fun and we could expand on that, but I hope you’re busy and having fun with the basics by now
(stuff used here : OS Voyager, Vox ToneLab ST, Gibson SG Standard, Ibanez AF75, Fender Geddy Lee Jazz Bass, M-Gear EX-P expression pedal, FC-300 midi foot controller, Little Phatty)
