Chorus effect design

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@dietcv asked me how to design a stereo chorus effect like in the Elektron Monomachine.

chorus
chorus491×807 122 KB

This post will be shorter than my usual fare as chorus effects don’t need to be complicated. Traditionally, chorus effects are accomplished with a delay with N taps, each modulated by a sine wave. The sine waves are offset in phase.

As an example, here is a diagram from the manual of the Akai S3000XL, which uses four delays and four LFOs:

chorus
chorus1415×1298 28.8 KB

Here’s a three-tap chorus, with the phases offset in an equilateral triangle:

(
{
	var dry, wet, snd, count;
	dry = Saw.ar(440);
	count = 3;
	wet = DelayC.ar(dry, 0.03, SinOsc.ar(0.1, (0..count - 1) / count * 2pi).linlin(-1, 1, 10e-3, 20e-3)).sum / sqrt(count);
	snd = (dry + wet) / sqrt(2);
	snd = snd ! 2 * 0.5;
}.play(fadeTime: 0);
)

Before people get on my case, yes, I am wastefully using multiple DelayCs on the same signal when I could be using DelTapRd/DelTapWr. Sue me. I will leave efficiency as an exercise for the reader.

By doubling to six taps and offsetting the phase of three of the taps by 2pi / 6, we can create a mono-to-stereo chorus effect:

(
{
	var dry, wet, snd, count;
	dry = Saw.ar(440);
	count = 3;
	wet = 2.collect { |i|
		DelayC.ar(dry, 0.03, SinOsc.ar(0.1, ((0..count - 1) + (i * 0.5)) / count * 2pi).linlin(-1, 1, 5e-3, 20e-3)).sum / sqrt(count);
	};
	snd = (dry + wet) / sqrt(2);
	snd = snd * 0.5;
}.play(fadeTime: 0);
)

It is also customary to add a feedback path across the chorus, in this case tamed with a DC blocker and a tanh:

(
{
	var dry, wet, snd, count;
	dry = Saw.ar(440);
	count = 3;
	wet = LeakDC.ar(LocalIn.ar(1)).tanh * 0.95; // turn up the feedback past 1 for some WILD sounds
	wet = wet + dry;
	wet = 2.collect { |i|
		DelayC.ar(wet, 0.03, SinOsc.ar(0.1, ((0..count - 1) + (i * 0.5)) / count * 2pi).linlin(-1, 1, 5e-3, 20e-3)).sum / sqrt(count);
	};
	LocalOut.ar(wet.sum);
	snd = (dry + wet) / sqrt(2);
	snd = snd * 0.5;
}.play(fadeTime: 0);
)

If you don’t like how my chorus sounds, that’s fine — feel free to tune parameters to taste.

While a good-sounding chorus effect is easy to build, there are many possible variations on this basic form. Some ideas I can think of right now: use LFNoise2 instead of SinOsc, try using pitch shifters instead of delay line modulation, or crossbreeding chorus with other effects like distortion and granular.

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