[sdiy] 1V/oct CV-phaser

[eq927 at freenet.carleton.ca]

A phaser with 1V/oct control of "center frequency" is a very powerful 
tool for sound manipulation... at least for sounds with complex spectra 
or large harmonic content - even though the notches (or peaks) are not 
harmonically related, changing the "phaser center frequency" will 
maintain the frequency ratios between the individual notches (or peaks), 
and the resulting timbre will track the keyboard. You could tune an 
individual notch or peak to track a particular harmonic across the 
keyboard.
 
  A 1 V/oct phaser is a specialized type of VCF, (a tracking comb 
filter), which is capable of drastically altering the tonality of a 
complex signal, with a minimum of "knob-twiddling" required, as compared 
to a filterbank, so offers a lot of bang for the buck.

A fairly simple 1V/oct phaser could be built along the lines of the 
Electroharmonix Small Stone phaser, using an exponential current source 
to provide the Iabc for each OTA, rather than using the existing sweep 
circuit in that phaser. LM13600/LM13700 would be a good choice of OTA 
for this (the CA3094 is no longer available).
Mike