Compressor Technical Definitions

[deparisn]

Hi Everyone,

What in technical spec terms does Level, Ratio , Sustain, Attack paramters for a compressor consist of. Like for instance, does the level knob change the amplitude of the signal from xdb to ydb. I am looking mainly at the BYOC 5 knob compressor.

Attack is defined as how quickly the compressor reacts to pick attack, whst the heck does that mean technically.

[Kipper4]

Hi Everyone,

What in technical spec terms does Level, Ratio , Sustain, Attack paramters for a compressor consist of. Like for instance, does the level knob change the amplitude of the signal from xdb to ydb. I am looking mainly at the BYOC 5 knob compressor.

Attack is defined as how quickly the compressor reacts to pick attack, whst the heck does that mean technically.

Level is usually a make up volume after the compressor part of the circuit. so say you have lost a little or lot of signal during compression this is put back at the output with the level knob.

Ratio is the amount of compression applied to the signal. Eg say the ratio is 2:1 for every 1db over the compressors threshold 2db are shaved off as it where by the compressor.

Sustain is the amount of sustain held during compression.

Attack is how long in milli seconds before the compressor kicks in an attenuates the signal. so say you st the compressors attack to 5 milli seconds. You play a note and 5 milli seconds after the compressor does its thing.

All sorts of differant effects can be had by playing with the differant perameters
I think I have that right. I'm sure someone will correct me if not
Rich

[deparisn]

Thanks Rich. No that helps a lot. Trying little battles you know. Um do you happen to know how long the attack can be for the BYOC 5 Knob?

[Kipper4]

Sorry buddy I don't know the answer to t hat one.
Maybe go to the BYOC forum and ask.
Welcome to DIYSB btw.

[deparisn]

Thank you Kipper4, it did help though. I had to redefine what I wanted to do for my project. I am really trying to compare the difference between a tube and a solidstate compressor.

[Kipper4]

Well if it helps they both compress period.
Why get a tube compressor? Are you thinkig that you will get a mojo sound ?
Is it for guitar use?
I've had (made) quite a few compressors and my favorite right now is the Ross Dyna comp for guitar.
Theres lots of easy to build, simple low parts compressors around here. Try the search facility mate.

[midwayfair]

Read RG Keen's breakdown of the Dynacomp.

"Sustain" works sort of like a threshold control in the Dynacomp. It's setting the maximum effect that the compression can have. It also kind of affects the ratio -- higher settings will result in a greater reduction in gain. In the 5-knob, though, the ratio control is literally the ratio between the unaffected signal and the compression effect.

Attack and decay are both time constants -- they work out to a certain number of milliseconds. The attack is a low pass filter of some sort, but I don't have a good description for how it works in this particular circuit. Hopefully someone else will come along to describe it.

[deparisn]

Well if it helps they both compress period.
Why get a tube compressor? Are you thinkig that you will get a mojo sound ?
Is it for guitar use?
I've had (made) quite a few compressors and my favorite right now is the Ross Dyna comp for guitar.
Theres lots of easy to build, simple low parts compressors around here. Try the search facility mate.

No I am researching the difference in the sound characteristics.

[Mark Hammer]

What gets called "Attack" on the vast majority of stompbox compressors is nothing of the sort.  It certainly gets labelled as "attack", though.  I suspect this is largely because it's difficult to explain to people what he control actually does (and won't do), easier to yield to peer pressure and call it what everyone else has previously called it, and is a sexier term than what it ought to be called.

The rectifier circuit will result in a signal that, in response to transients in the signal, pulls the gain down/back from whatever it was a moment ago.  If the spedomoter and tachometer on your car sampled the speed or engine rotation 40 times a second and kept updating it at that rate, it would simply deliver visual noise to the driver.  So, it averages everything out, and introduces a certain amount of lag in the information it displays.  Similarly, the rectifier also averages out all those transients, and introduces some lag.  The audible result is that when it quickly reduces gain in response to a transient, it takes a bit of time to "catch up" again, and resume maximum gain.  The compressor essentially says "Yeah, yeah, hold your horses, I'm coming.  Let me get my shoes on first!".  The control adjusts "gain recovery time", but like I say, its not what people want to call it on their pedals, and they sure don't want to have to explain it to customers.

This "attack" control adjusts how long it takes for the circuit to get its shoes on and bring the gain back up.  Because compressors deal with rapid-fire events, and process rapid-fire events, the amount of time one has dictated for the rectifier circuit to get back up to speed might be quick enough to deal with the next transient...or may be too slow to deal with it.  If you leave a lot of time between successively picked notes, then chances are pretty good that the gain will have come back up again since the last picked note, and you will actually hear the pick attack as nature and physics intended it.  If you are picking fast, and the gain recovery time is super-quick, you will also hearthe pick attack reasonable well.  If you are picking fast but the recovery time is too slow, note N pick attack may be heard well enough, but notes N+1, N+2, etc. will be picked before the full gain has resumed, and their respective pick attack will sound very subdued, as a result.  YOu'll certainly hear it, but it won't stick out the same way as if you weren't using compression at all.

So, even though the control does NOT change the attack time of the compression, it does have an impact on the perceived attack of rapid-fire notes.  So that's why they call it what they do.  In more full-featured limiter/compressor units, like the Empress (locally made in my city), that have separate Attack and Release controls, those Attack controls actually DO adjust how quick the gain gets pulled back, as opposed to how quickly it gets restored.  I could be wrong, but my sense is that if you see a stompbox that ONLY has a pot labelled Attack, and nothing else to adjust time in any way, then such a control will be of the gain-recovery-adjustment type.

Since the audible impact will depend most on how you pick, it is a highly misunderstood control, since its impact is not nearly as obvious as a tone or volume control, or a speed/rate control on a modulation effect.  Personally, I suspect that most players will set such a control to the one extreme setting or the other most of the time, if only because it's hard to detect as your picking rate changes.  But that won't stop consumers from feeling like they are missing out on something if they don't have it as a continuous control.  Some years back I helped another local pedal-maker, Retro-Sonic, come up with a viable 3-position recovery-time switch for his Ross clone.  He implemented it, and it worked well (as well as on EHX's current-issue Soul Preacher).  A few years later, I noticed it had been replaced with a pot.  When I asked why, Tim told me that customers had kept asking for a control, so he finally had to give in to pressure.  I'm pretty certain that the majority of subsequent buyers set that pot to min or max most of the time.

That face-palm aside, now you know how the Attack control works, why it can sometimes seem like it doesn't, and why it is mislabelled.

[tubegeek]

http://www.rane.com/digi-dic.html