So what makes a compressor fast or slow electronically?

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BobbyRay
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So what makes a compressor fast or slow electronically?

Post by BobbyRay » Mon Dec 20, 2004 9:27 am

So what makes a compressor fast or slow electronically? I have the Art pro vla, I really like the tone on this thing however it's pretty slow. Is this something that could be modded easily or would it be more trouble than it's worth (like putting turbo on a geo metro)? I am a home studio guy so lets keep the answer pretty easy to understand if possible.

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Re: So what makes a compressor fast or slow electronically?

Post by SeventhCircle » Mon Dec 20, 2004 10:15 am

Generally speaking, an analog audio compressor consists of an input buffer, a variable gain element, an output buffer, and some "side chain" circuitry. Compressors are categorized according to their gain reduction circuits, such as opto, JFET, variable mu, VCA, diode bridge, etc. Each of these circuits has its own unique characteristics, and each can be made to work well. Some of them are inherently "faster" than others, but all can be made to respond to even the shortest audio signals.

The side chain is basically a low-pass filter that controls the variable gain element. The response if this filter is primarily responsible for the attack and release times of the compressor. Some side chain circuits allow extensive user control of attack and release times, some don't allow any.

In order to mod your ART box, first you have to understand the limitations of the variable gain element, then you need to figure out how the sidechain filters work. You'll need a schematic for sure, and some test equipment will be helpful. Good luck.


BobbyRay
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Re: So what makes a compressor fast or slow electronically?

Post by BobbyRay » Mon Dec 20, 2004 2:31 pm

I was hopping that maybe there would be a couple of parts that could be upgraded, like when people replace the opamps in other economy gear.

I liked this pro vla thing a lot when I first got it. Now when I'm using it in a final mix I started to notice it would let the first note slip by untill it clamped down even with slight comp. and fast attack.

Joel Hamilton Posted: Mon 20.12.04, 2:24 pm

Slow is good.


Really? ...what do you use slow compression on Joel?

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Tim Farrant
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Re: So what makes a compressor fast or slow electronically?

Post by Tim Farrant » Mon Dec 20, 2004 6:19 pm

I read on the ART website the fast attack time of the VLA is quoted at 2mS (for 20dB gain reduction). If this is correct, then you should be getting better results than you describe because 2mS is only 2 cycles of a 1kHz sinewave.

You can of course check this out for yourself by recording on your DAW a series of 1kHz tone bursts, playing these thru the compressor and recording it back into you DAW. You can then count how many cycles of the 1kHz signal it takes for the compressor to grab the tone, each cycle being 1mS. I could be wrong, but I think you might find it's actually closer to 10mS attack time, which is typical of of LED/LDR optical elements. There are of course ways to speed this up electronically (as used in our opto comp), which may have been implemented in the VLA, I don't know.

I would be interested in seeing the results of the above test.

Cheers
Tim.

jajjguy
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Re: So what makes a compressor fast or slow electronically?

Post by jajjguy » Mon Dec 20, 2004 7:23 pm

BobbyRay wrote:Really? ...what do you use slow compression on Joel?
i'm not joel, but: vocals. not that fast compression has no place with vocals. maybe some of both. :D

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