There are plenty of off the shelf compressors you can buy.
However by building one yourself, you'll learn the principles of how they work.
You can actually build a compressor with a envelope follower, a an
inverter and a VCA.
A modular compressor is essentially a voltage
controlled envelope follower tied to a VCA.
The 4 basic components:
1. Mult
2. VCA (linear preferably but a exp VCA will work too)
3. Inverter / attenuverter
4. envelope follower
First split the signal into two.
a. the original signal (A) to be compressed.
b. the side chain detector signal (B)
Signal A --> envelope follower ----> inverter ------> CV input of VCA
Signal B --------> audio input of VCA
The fun thing about building your own compressor is varying the components.
The VCA for example could be vactrol based LPGs
You could use a Make Noise Maths. It could perform the envelope follower & voltage inverter tasks.
A serge DUSG could do this as well, as could the Doepfer VCS( A-171-2).
This is a patch for compressing a bass drum
In this example channel 4 is acting like a slew limiter.
It's output is plugged into the input of channel 3. It's in inverter mode.... creating an inverted
version of channel 4.
Chanel 2 of the maths is simply amplifying the straight audio of the bass drum.
It's then going into the second audio input of the VCA.
I'm using the HP filter to remove some of the lower frequencies. I could also use an EQ.
The delay has lots of CV inputs which could be modulated with LFOs, the Maths, sequencers, or EGs.
The Doepfer A-119 envelope follower has a voltage comparator with a gate output that can be used to trigger envelopes.
Of course the signal processed in the VCA doesn't have to be the same signal that is being analysed by the envelope follower. The open architecture of a modular synthesizer allows you to design any kind of side-chain compression scenario your heart desires.
Another interesting module is the Bastl Dynamo.
Its just 5HP and contains two Envelope Followers with inverted and non-inverted
Envelope Follower Output. There is also a Compressor CV Output with indication LED
(only negative voltage when envelope is greater than the threshold.
When the Compressor CV is plugged into CV input of a VCA with offset and attenuator knobs you get an Compressor!
Extra modules that would come in handy
5. mixer
6. Slew Limiter
7. EQ
8. filters
9. comparator
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