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.