Anyone ever make an envelope swept or expression controlled chorus/vibrato?

[spectraljulian]

I love how my Polyphase has 3 different modes of control, and I think a chorus with envelope and expression sweep could be really cool on my clone theory. 

It could be something like this

knobs- blend, LFO rate, LFO depth, envelope sensitivity

switches- LFO on/off, envelope- off/rate/sweep, expression- off/rate/sweep

I'm more of a modder/bender than a full circuit builder but I think I might make something like that in the future. 

[Mark Hammer]

Essentially anything where a parameter is controlled by a single varying resistance lends itself to envelope control.  For instance, the LFO rate in the Tonepad "Heladito" clone of the E-H Small Clone pedal is set by a single variable 1M resistance.  As that resistance gets smaller, the speed goes up.  If you placed an LDR in parallel with the speed pot, you could arrange to have the speed increased as you picked harder by using an optoisolator to harness the guitar's envelope.  Note that, because we're looking at the combined parallel resistance of two things (pot and LDR) the degree of envelope influence will depend on the setting of both the speed pot and the envelope-detector's sensitivity.  Not a huge problem, as long as one is mindful of the interactive nature of the two elements in setting the final combined parallel resistance.

The intensity of the effect is contingent on the mix/blend of the dry and wet (delayed) signals.  If one added a wet-level variable resistor in series with the stock fixed resistor that sets a 50-50 blend for the wet side, y could place an LED/LDR combination in parallel with that pot as well, to achieve a sort of chorus-on-demand effect that faded the wet level way in the background when playing softly and moved towards a 50-50 mix (the most audible chorus effect) as you picked harder.

Note that these two forms of control can be used individually OR in combination, though you'd need two optoisolators to do it.  Note as well that the time constant for the envelope follower would likely need to be longer.  A fast attack/decay may be fine for a compressor or envelope-controlled filter, but when using envelope strength to adjust the flavour of a parameter, you want it to take a little while longer to make the transistions.

I have a major rackmount phaser project that I'm going to attempt in a week and a half that will involve envelope control of rate, regeneration amount, and intensity, both individually and in combination.  What I need to find now is a 3-pole 6-position rotary switch.  Whether a single envelope-sensitiviyt control is sufficient to use two or all three forms of control at once is an empirical question that I'm eager to find out.

Finally, while envelope control as a substitute for manual sweep can work well in some types of effects (e.g., the Line 6 Tonecore Liqui-Flange I have includes envelope-controlled flanging, and envelope-swept phasing will sound good too), envelope swept chorusing WILL suck, simply because the nature of the effect demands that there by constant modulation of the wet signal to produce the thickening effect.  Note that where flanging and phasing have a filtering effect (and the Liqui-flange makes an excellent auto-wah in its own right!), the principle aspect of chorus is the pitch shifting, NOT the notch filtering.  I won't claim that you'd get nothing of interest by ganging envelope-control directly to the clock, but it sure as hell won't sound like chorus.