Compressor with variable ratio

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What would a compressor with an input linked ratio be called? It's not knee, since that only smooths the transition to one ratio, as far as I understand it. A graphic compressor?

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Non-linear distortion.

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^ this. A simple waveshaper - not a compressor in the common sense.
Fabien from Tokyo Dawn Records

Check out my audio processors over at the Tokyo Dawn Labs!

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I'm not following. A waveshaper is a non-linear function in-to-out to my definition. The ratio is how the gain reduction is determined from the level detector. A downward compressor will have a gain factor of 1 below the threshold and above it is determined by the ratio, and then attack and release are also present.

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camsr wrote:What would a compressor with an input linked ratio be called? It's not knee, since that only smooths the transition to one ratio, as far as I understand it. A graphic compressor?
LED Compressor :wink:

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Would you call it a compressor-limiter? That name may be over-used and not specific enough. Dunno.

Assuming that you mean that the compressor would enter gain reduction very soft knee, then get continually higher ratio with higher input. If the user interface would allow odder arbitrary mappings then the name probably would not be appropriate.

That variable ratio culminating in limiting is a fairly common characteristic of feed-back topology with some types of gain elements.

It is the approximate response of one of the simplest to build "musically acceptable" analog compressors. There is only a compression amount knob, which controls a variable gain amp driving the LED of a clairex clm 6000 opto isolator. The light cell of the optoisolator is in an attenuation circuit upstream of the compression amount knob.

The response curve of the various elements leads to a gradual entry into limiting.

The simple circuit is a pumping monster, but some folks like that slow response extreme pumping.

Opto compressors can use various optical drivers and light sensitive elements. If using cds cells, you can't just pick one off the shelf at radio shack. You need one with certain light response characteristics and timing characteristics. And many generic cds cells can have different resistance depending on voltage level and polarity, so the odds favor distortion city in some randomly selected generic cds cell.

The feed-back topology is perfect for opto compressors, because the gain response of the parts are so spotty and difficult to specify, the feedback makes them "better behaved". They are generally not linear enough to use feedforward.

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Digital is linear enough! :hyper:
This answers my question then, the correct "buzz word" is opto.
I was just fooling with a compander made with some very simple core components in Reaktor. It sounded good but it doesn't use an attack/release system, only "program material". It took all but 10 minutes to wire up, so you know it's simple.

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"Variable MU" and "Opto" are just means of creating hardware voltage-controlled gain elements. It's not really the answer to your question. The shape of the compression curve is affected by those elements but it also has a lot to do with the envelope detection path and how that signal is generated and treated - which is really what your question is about.

What you are asking here can have two different meanings. If the the compression ratio is related to the ABSOLUTE level of the input signal then it is most likely a "soft knee". Aphex built a compressor called the Compellor that has a very soft knee over a 20-30dB range. The higher the input signal level gets the harder it compresses (more ratio). Because the knee is so soft it can be very transparent if not pushed too hard.

The ratio can also be a function of RELATIVE level. In other words, how much the signal level is jumping around with respect to its own average level. In that case what you have is program dependent/relative compression/expansion and is used in "transient modifiers".

And, of course, you can combine the two processes in a multitude of unique ways - and that's what many of the really good, high-end units do. The "secret recipes" if you will.

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Thanks Fender your advice is invaluable.

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camsr wrote:Thanks Fender your advice is invaluable.
I don't know if it's invaluable but I hope it helps!

I used the techniques I mentioned above in my Rocksonics MB-3X, PL-2 and DRP-2a hardware compressors, the opto CAJ V-Comp tube compressor and the "RT Maximizer" plugins.

I don't know how to write code like many of you guys - especially the fancy GUI stuff - but I know how compressors work. (At least some of them.) :)

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They can do some amazing things, sometimes.

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