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previous: Arnaud Hi !I've dreamt a l... -- 8/19/1999 8:18 AM view thread

Re: EH Polyphase

8/19/1999 1:29 PM
Mark HammerRe: EH Polyphase
Three aspects to envelope-controlled phasing.  
1) Sweep itself is driven by the envelope: This is simple to do. Use a photocell-based phaser design, and drive the LED coupled to the photocells with an envelope detector. You could easily adapt the Mutron design by substituting phase shift stages for the state-variable filter in there already. Also done with FET's but this requires more tinkering.  
2) Sweep RATE is driven by the envelope: I think this is what the Polyphase does. Essentially, you set an initial sweep rate, and the control-voltage from the envelope detector is summed with the existing control voltage that drives the sweep LFO.  
3) Simultaneous driving of sweep width and rate: Same deal, only your envelope detector sends a control voltage to two different paths, each of which could be mixed in to taste. E.g., picking strength would have a small effect on sweep rate, but a more substantial effect on sweep width.  
As an addendum, 20 years ago, when Craig Anderton was publishing DEVICE magazine (the table of contents of which are supposed to be archived here at AMPAGE), he designed different modules for a guitar processing system that was intended to produce synthesizer-like control without doing pitch extraction. One of the modules was a "pluck detector", that summed indicators of pick attack (which could be either trigger pulses coming from a trigger extractor) over multiple plucks, to produce a control voltage that varied as a function of how many notes your were playing (i.e., how fast), rather than how strong each pluck itself is. Something like this is probably more appropriate to driving the LFO rate of a phaser than the standard envelope detector.

Arnaud Thank you for this information, Mar... -- 8/19/1999 4:55 PM
tboy q{..the table of contents of which ... -- 8/20/1999 9:17 AM