Attack And Release

B

bdam123

Member
I'm going to have to apologize for yet another Compressor Question but I'm attempting to make leeway in my understanding these things.

I understand that the attack time is the time it which it takes the compressor from the point the threshold is passed to finish clamping down on the audio. It is NOT the time it takes, after the threshold is broken, for the compressor to START compressing.

My question is how does the release actually work? Does the release start as soon as the attack time is over? Or does it wait for the signal to fall under the threshold before it begins to release?

Thanks
 
Attack and release are both time constants, e.g. "10dB per second", the rates at which the gain can decrease (attack) or increase (release). Signal level, threshold and ratio all combine to produce a target gain reduction value while attack and release determine how fast the gain is changed toward that goal. Attack and release don't really respond directly to threshold crossings.
 
In simplest terms you could say that the release "starts" as soon as the signal drops back below the threshold. It is, of course, not that simple. This is not a triggered envelope like you might have on a synthesizer where it goes through its A(DS)R routine every time it's triggered. It "starts" heading toward full compression from wherever it is whenever the signal goes above the threshold, and heads back to linearity as soon as it drops below - even if it hasn't got to full compression yet. In fact, in most situations you never actually get to full compression, though you might get within a **** hair.

The truth is that the signal is crossing the threshold pretty rapidly (four times per wave cycle on a big enough sine wave). The A and R controls actually act pretty much like (extremely) low pass filters in the detector path, only the cutoff frequency changes dependent on how loud the signal is.

In practice, you just turn the knobs until it sounds the way you want, but a deeper understanding of how it actually work can help you find a starting place quicker.
 
Still confused haha.

They reason why I'm trying to understand is because my ears still aren't fully trained to hear exactly whats going on.

Sometimes I don't even hear a difference between different setting.
 
If you're trying to train your ear to hear compression, experiment with a bass guitar track. The attack time especially makes a massive difference in what you hear. The bass note takes a short period of time to develop. A longer attack time on the compressor gives the note time to develop before it starts clamping down. You hear more of the initial thump. The bass sounds punchier. A shorter attack time compresses that thump. It can make the bass sound muddy or indistinct in a mix. Release time is more subtle, at least it seems to me. If the you set it too short, you'll begin to hear artifacts as the sound seems to bloom as the compressor releases while the note is still sounding. A longer release time sounds more natural to me.
 
If you're trying to teach yourself about compression (and it's one of the most complex things in your tool box), my favourite resource is the Rane Notes on the topic, available HERE.
 
Snare is an interesting source for practicing compression. It has a nice transient at the start for experimenting with attack and some resonance that will show what release does.
 
Two things you can do to train your ear for compression:

#1. Grab a loop of a drum kit hammering out a medium tempo groove. Compress it using the fastest possible attack and release, ratio around 4 or 5:1, low-ish threshold (getting around -10dB or so of reduction). You'll be hearing a lot of the room sound, but the drums themselves will be contained. Now back off the attack (slow it down) and you'll get transients starting to pop through (and you'll likely have to reduce your make-up gain to avoid clipping the next device in line). Next, slow the release and the room sound will be reduced. The reason you hear so much room with the fast release is that by 'releasing' the gain reduction the unit is effectively 'turning up' the level after the initial reduction,... really fast (so the room sound that is normally below the drum information is effectively gained up before the natural ambience dies away. The slower the attack the more transients are let through (which produces the snapping you hear as you slow the attack).

#2 grab an intimate, uncompressed vocal track. Use 3:1 ratio, fast attack, medium-slow release, adjust threshold to get around -6dB reduction, perhaps a touch more (which is a lot, but we're ear training here, so the greater the reduction the easier it is to hear what is happening). Listen to how close (or not) the vocal 'feels' to the listener. Now relax the attack control, so that more of the leading edges of the consonants get through before the reduction happens. As the attack slows notice what happens to the feeling of intimacy in the vocal track (or put another way, notice how it feels closer as the attack slows and more transients get through unmolested.). Now speed up the release and notice how closer, still, the vocal feels? With slower attack more transients get through, and it feels close. The fast release means the the lower level information at the ends of words and phrases is very present too (again, as the in the drum loop example above, the fast release 'turns up' the level quickly after the initial reduction, which makes it very present).

So a fast attack with medium-slow release will chop the leading transients of words and will keep the low level end-of-phrase information at a lower level = a farther away feeling. Slower attack with fast release will allow more transients through (more in-your-face feeling) and will raise the level of end-of-phrase information, making it too feel more present.

Feel free to use more extreme settings and overall reduction to maximize your ability to hear these things. With the drum loop example it should be pretty easy to 'hear.' With the vocal example it will be more a near/far 'feeling' that you're perceiving. These should get you on your way to training your ear for compression.

Hope this helps.

Joel
 
https://www.youtube.com/watch?v=AKS7EdK0dPY

It's a long video, but Eric Tarr is BRILLIANT at explaining the specifics of what you're hearing in a way you can see.

If you're having any issues with understanding what exactly happens with attack and release, I suggest taking 15 minutes and watching this video.

EDIT: I'd like to note that he just shows how a compressor affects a signal that's at a constant level. This will help you see what attack and release times are doing once a signal reaches a threshold, but it's still up to you to train your ear to how these things sound on real world sources!
 
hit the nail on the head ashcat.. turn the knobs( with a little understanding of what's going on when you do that ) and find the sound you want.
 
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