Compressing Modulars?

media at media at
Mon Nov 17 23:50:08 CET 1997

At 1:32 AM -0600 11/17/97, Roy Tate wrote:
>R. Fahl wrote:
>>That leads me to this question:  Would it make more sense to build a set of
>>compressor modules, or should I just go and get myself a multichannel unit,
>>such as the Behringer Multicom.  I want to keep the signal path as clean as

I'd like to think that you could design a better compressor than a
Behringer Multicom :)  With the popularity of MDM's, there are several
eight-channel units on the market.

>I've been considering this idea as well.  The SSM2122 (or some successor),
>the NE570, and several others offer an easy way to make a compressor.

Analog Devices is an excellent source of VCA chips.  They make the chips
for several famous compressor manufacturers, including Focusrite.

They even make a SSM2024 (??) which is a current controlled amplifier.

All that being said, I've seen plenty of compressors that did not use VCA
chips.  I don't mean valve designs, but those built around "regular"
op-amps (NE5532, TLO72, etc.) using either solid-state or optical

>One half of the circuit converts the current signal level to a control
>voltage (a precision rectifier), and some additional circuitry controls a
>VCA.  >The rectifier could have a direct out and be uses as an envelope
>follower, and
>the VCA could be fed a different signal than the rectifier, offering a
>full-featured compressor.
>Or, you could just have a switch on your VCA to control whether the
>rectifier + compressor circuit kicks in.  This would be a minimalist
>thing, with a switch and knobs for threshold and ratio.
>The next question:  would a "simple" compressor with hard-knee
>be acceptable?

Actually, I think Romeo is describing more of a limiter than a full-time
compressor.  I'm under the impression that he is trying to prevent clipping
rather than deliberately change the sound.

Anyway, he could add in a "lag processor" (what is the difference between a
lag processor and a low-pass filter, btw??) before the control input to the
VCA to smooth out the response.

At 10:50 AM +0100 11/17/97, Haible Juergen wrote:
>I know it's just my opinion, but I try to use as few compressors on
>electronic instruments as possible. Your *Modular* synth is too loud ??
>Well, you have the core of a compressor, a VCA, at the end of your
>Modular's signal path anyway. So why messing the signals up with
>another VCA (the compressor's) ? All you need is the right CV for your
>Synth's VCA. Does the Sustain pot of your envelopes have linear or
>logatithmic response? The VCA itself: linear or exponential?
>I'm asking this because the *input* level of your average synth VCA is
>most probably quite limited anyway (speaking of otas - not of "pro"
>vca's like dbx chips etc.). So the VCA CV may be the key to the

That is a very good point.  Given the description above, I wonder how great
a dynamic range this synth has.  In my experience, synths typically have
less dynamic range than decent mic pre's.  Maybe he could just add an
attenuator (such as a voltage divider to ground) after the VCA or VCF or
whatever is the last module before he sends it to the mixer.  I'm assuming
his mixer is already potted all the way down.

>> Also, I am using a 16 channel Boss mixer.  I use it because it was all
>> I could afford when I needed a mixer.  Would a Mackie be able to better
>> handle the output of my modular?

I am not familiar with your specific mixer, but I do remember using a 12-ch
Boss that was very noisy.  It also was not designed to accept -10 line
level, not +4.  If your intention is to increase dynamic range, you should
seek out a mixer that not only can accept hotter voltages but also has a
lower noise floor.  A noisy mixer that isn't clipping isn't much of an
improvement over padding the input to your 16-ch Boss.

Another thing to consider is that even though the signal might not be
distorting on each individual channel it still may be clipping at the
summing amps  -- this may not be apparent by simply watching the meters.


P.S.  Thanks to everyone who has sent me info on building filters!!

"I know that I can come off as a little proactive, and for that I'm sorry."
                                                  --  Homer Simpson

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