Building a Simple Mono Compressor with Doepfer A-100 Modules
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Hi folks,

I was thinking about building a compressor with the A-100 modules. Because I don't have all necessary modules to realize it yet, maybe someone of you who have them, could try it and tell my how it sounds and of works anyway.
I'm desperate to know, how it sounds. Maybe some could send me an audio sample, not processed and processed.

Modules needed:
A-119 Ext.In/Envelope Follower
A-140 ADSR or Quad-ADSR
A-133 Dual VC Polarizer
A-132-3 Dual VCA or any other exp. VCA

You can find my patch suggestion here:
http://homepages.physik.uni-muenchen.de/~Oliver.Gretz/a-100/Doepfer-Simple-Mono-Comp.jpg

The Envelope Follower generates the gate signal to trigger the ADSR and an envelope which is used to control the compression ratio. Here, the threshold knob on Envelope Follower function just as well as the threshold knob on a compressor. You just have to start from value 10 instead from 0.
The ADSR triggered by the Envelope Follower generates the envelope, how you want your signal compressed. Usually attack-decay volume attenuation envelopes are sufficient, but of course you can make it more complex with sustain and release or with any other modules.
Although the ADSR signal is positive, it will be inverted by a voltage controled polarizer. The ratio how strong the ADSR signal should be inverted is controlled by the inverted envelope, originates from the Envelope Follower, which represence the volume of the input signal. Therefore the higher the volume of the input signal is, the higher the volume of the original signal will be reduced by the VCA. And right so how you have set the threshold and attack and decay values.
Depending on how heavy you compress the audio signal, you could need a second VCA to get the overall volume louder. I don't know, try it out.

You could easily expand this patch suggestion to a stereo compressor with a second A-119 Envelope Follower and a second VCA.
You could also make the compression smoother by low-pass filter the A-119 envelope signal or using a slew limiter.
If the A-119 module would have had a seperate envelope follower input jack, you could high pass or low pass filter the audio signal to easily realize a sidechain compressor (to get the pumping effect as well no pumping at all).

This really just a very simple implementation of a typical compression process. So don't be to strict to me. ;)
As I have already said I don't have the modules at home to try it for my self. There are good chances that there is something wrong. So don't hesitate to tell me the mistake.

Have a lot of fun,
Ollie