tkingen said:
For the newbie (and not so newbie) compression can be a confusing thing. Even after reading explanations of how compression works it can still be difficult for a novice to put the knowledge to practical use.
So, to all of you who are well versed in using compression - what goes through your mind while you are deciding if you need to compress and how do you decide how to set threshold, ratio, attack and release?
What I'm looking for is a description of your inner dialog that helps you achieve your goals.
I think the one thing that pretty much broke it all right through for me is the understanding that
sound has density.
Not only does sound have density, but it also has shape. And when I say sound, I guess I'm refering the
dynamics of sound as having coordinates in time; there is a beginning to a sound, a middle and an end. And along this continuum, the volume will vary.
Attack, release, ratio, etc. all have to do with what part or parts of the sound you wish to emphasize. In a vocal track, for instance, a slower attack time will have the effect of emphasizing the beginnings of words. This is because the initial consonant sounds the mouth makes are allowed to "pass" before the compressor kicks in ... thus, raising the volume of these beginnings of words in relation to the rest of the word. Ditto for the attack of the pick, or finger, on a guitar string.
Similarly, you can emphasize the endings of the words by using a very short release time. The release time, as you probably know, is the amount of time it takes to bring the volume back up after compressing. If you bring it back up fast enough (by using a shorter release time), it can raise the volume back up before the ends of the words are formed -- thus raising their volume.
By combining the two -- slow attack, fast release -- you enhance the anunciation and clarity of the vocal track, since the beginnings and endings of words are louder.
By doing just the opposite (short attack, long release), you can emphasize the "meat" of the note.
This kinda' stuff is really important for drums, because it's such a dynamic instrument. Take a snare drum. Your stick hits the snare, making a really short, sharp "snap!" sound due to the impact of the stick on the drum head. What follows that is going to be the resonance of the snare's body, followed by the sound of the room reflections. Under normal conditions, the initial snap of the stick on snare might be so much louder than the ensuing resonance and ambience, that you lose a lot of that extra sound. Especially in a busy mix. All you might hear is a wimpy "ting!" or "tss!"
By using a short attack time, you can use a compressor to really bring out the rest of that sound that follows the stick hit. By doing this, you actually make the sound denser. You've literally compressed it so the loud parts and soft parts are closer in volume. And when a sound is denser, the human ear perceives it as being louder. This has to do with volume and our perception of time. Using the snare sample again ... by drawing out the resonance of the snare, followed by the room reflections, you've
elongated the snare hit.
You can see this stuff, literally, by looking at the wave form of a drum hit in your audio editor, pre and post compression. A snare hit who's initial impact jumps to "0" and instantly dies out won't sound as loud as a snare who's impact goes up to -5, but has some sustain by several milliseconds of resonance.
And therein lies the danger. Because of this, it's very easy to fall in to the trap of overdoing it. By overcompressing, you basically kill any differences between the louder and quieter parts of a sound. Thus destroying any liveliness.
Well-compressed:
POP!ppppp
POP!pppp
BANGboom
BAM!
Squashed to hell / over-compressed: POPPPPPPOPPPPPBANGBOOMBAM
In the squashed version, you just lost the points of emphasis and exclamation, along with any emotion that was contained within it.