compressor schematic

Magnus Danielson cfmd at swipnet.se
Mon Jul 3 22:53:06 CEST 2000


From: Martin Czech <czech at Micronas.Com>
Subject: compressor schematic
Date: Mon, 3 Jul 2000 13:12:05 +0200 (MET DST)

Martin,

> Has anybody a schematic of a studio dynamic compressor? No guitar effect.
> Just curious how real world devices work.

I have the schematics and the physical devices of both the ORBAN/PARASOUND
Model 418A Stereo Limiter as well as the Valley People Dyna-mite
Compressor Limiter. I think I have the schematics for the BSS compressor
around somewhere too.

There are really just two major design topics between diffrent devices:

1) Feed-forward vs. Feed-backwards design.

   In the feed forward design you detect the incomming signal, process the
   detected level and then feed the VCA which lies in the forward direction
   (of the signal).

   In the feed backward design you detect the outgoing signal and then feed
   the control signal backwards.

2) Detector types

   RMS detector

   Peak detector

   Averaging detector

   Really, the behaviour of the detector is really important. Here you should
   really consider the time aspects of a signal having peaks etc. Steady state
   is rather unintresting case really.

   Naturally will the time constants of an detector be of interest, and usually
   you can fiddle some wih that.

Further, once you have a topology and a suitable detector you have the
processing of the level signal, this will really create the instances of
noise gate, compressor, expander, limiter, infinit hold etc.

I can also contribute with my personal experience of problems to considering
the traps of designing compressors limiters. Bad compressor/limiter designs
can add quite a lot of distorsion you see ;)

Cheers,
Magnus






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