[sdiy] A question about Chorus

[Tom Wiltshire]

Hi All,

If I've got a classic chorus effect, with a delay modulated by an LFO, what exactly is going on?

The output from the delay line is a "vibrato" effect, e.g. the input signal is frequency-modulated (or the phase-modulated version anyway).

So can I assume that the standard FM equations apply, if I ignore the overall delay in the signal? I'm not especially interest in the fact that it's a sampled system. That's just standard nyquist stuff. I'm not expecting discrete maths here. Assume it's analog.

The reason I ask is that it just occurred to me that if a chorus is actually doing FM, then you ought to be able to mimic the effect of multiple delay lines by using more complex LFO waveforms. Each new sine wave in the modulating signal will generate a pair of sidebands in the output, won't it? Two sines modulating one delay would be equivalent to two delay lines set up for the same delay time, with two sine LFOs modulating them. The point being that that's considerably easier to implement, saving you input and output filters and a delay clock and delay line chip.

I suppose that for a genuinely complex sounding chorus, the fact that there are several different delay times also helps, but it seemed to me that the need for more delay lines could be reduced by using richer modulation waveforms than the usual sine/triangle.

Thanks,
Tom