MOTM

I had built a compander system around the Philips NE572 chips, but whatever 
I tried in terms of operating level and time constants, that thing did sound 
horrible. (That's the reason I hadn't published that part in the first 
place.)
Now I've replaced it with an OTA-based compander, similar to the one I had 
used in the FS-1 Frequency Shifter. Which, in turn, has been inspired by the 
compander inside the Roland Vocoder Plus.
It has an almost infinite compression ratio (more ALC that compressor), and 
it's feed-forward sidechain allows 2-pole filtering after the level detector 
for a very smooth operation. Frequency Shifters are quite demanding for 
compressors, as the output signal can be so much different from the input 
signal, and there is none of the cancellation of distortion products many 
traditional companding systems rely on. Here, in the Matrix FX, the 
expander's control current is directly copied from the compressor's - and 
not derived from the expander's input signal. The only drawback of this 
method is that the CV is "a little too fast" compared with the signal, which 
is slighly delayed in the dome filter. I practise, this wasn't a problem, 
however.

See http://jhaible.heim.at/matrix_fx/jh_matrix_fx.html - the new stuff is 
highlighted in Red.

JH.