Making a “wah” synth in FoxDot

René Ghosh, 20/12/2018

Possibly from growing up in the seventies, I have a deep affection for the wah sound. Anyways, I was trying out various synths and effects in FoxDot and couldn’t find anything that approximated this awesome sound. The beauty of using FoxDot is that, is you’re not happy with any of the out-of-box synths, you can easily make your own.

Making warpy

As a starting point, I used the arpy synth, which looks like this:

arpy = SynthDef("arpy")
arpy.freq = arpy.freq / 2
arpy.amp  = arpy.amp * 2
arpy.freq = arpy.freq + [0,0.5]
arpy.osc  = LPF.ar(Impulse.ar(arpy.freq), 3000)
arpy.env  = Env.perc(sus=arpy.sus * 0.25)
arpy.add()

Basically, it takes a pitch, adds another one at half-frequency, converts it into an impulse oscillator and pushes it out with a percussive enveloppe. This is perfect to add a wah to.

Here’s my version of arpy + wah, which I’ve tentatively named “warpy”. Starting from the same code base, I stretched the envelope to the full sustain length, then modulated the oscillator with a low-pass filter that shifts in time from two functions:

• LFNoise1, to add some randomness to each note played
• XLine, to make the filter’s frequency threshold move up exponentially as the note is played. This is what produces the characteristic “wah” sound.

I added some distortion to the signal to dirty it up a little.

with SynthDef("warpy") as warpy:
  warpy.freq = warpy.freq / 2
  warpy.amp  = warpy.amp * 2
  warpy.freq = warpy.freq + [0,0.5]
  warpy.osc  = LPF.ar(Impulse.ar(warpy.freq), 3000)
  warpy.env  = Env.perc(sus=warpy.sus * 1.00)
  warpy.osc = RLPF.ar(warpy.osc,
    LFNoise1.kr(warpy.sus,warpy.freq*3,warpy.freq*3)
    +XLine.kr(30,warpy.freq*3, warpy.sus), 0.07, 10).distort*1.25

So what does it sound like?

To demonstrate the effect, here is a short recording of a riff done with both arpy and warpy:

Scale.default = "chromatic"

b1 >> arpy([12,7,12,7,10,10,7,10,7], dur=[1,1,1,1,0.5,.5,1,1,1], oct=4)

b1.stop() #listen to the arpy version, then warpy

b1 >> warpy([12,7,12,7,10,10,7,10,7], dur=[1,1,1,1,0.5,.5,1,1,1], oct=4)

Played with arpy, it sounds like this:

This is what the same riff sounds like in warpy:

Conclusion

Anyone making music in FoxDot will want to customize the instruments to their own liking and make a characteristic sound. Beyond changing the effects stack to achieve this, it’s relatively easy to make one’s own library of custom synths. It just takes a little experimentation.

Happy FoxDoting!