The compression question thread

[Metaltastic]

I feel that compression is one of the most useful but also one of the most misunderstood concepts in audio production, and without wanting to be too ambitious, I'm of the hope that my questions (and hopefully their answers) here can inspire others to ask similar questions in this same thread, leading eventually to a sticky. Really, I understand the concept of a compressor and the terminology, as well as most of the controls (threshold, ratio, make-up gain, etc.) However, attack and especially release times still really elude me; I obviously know what they control, I just am really not sure as to their use. So here are my questions:

1) When trying to "smash" something (usually vocals/bass, as well as any parallel compression), wouldn't one always want to use the fastest attack possible? The way I see it is you're trying to even out the volume, so even letting a little transient through before clamping down seems like it would defeat the purpose.

2) By the same token, when trying to "smash" something, why wouldn't one always want the fastest release? To me, that seems like it'd be the most transparent, cuz I'd imagine it'd be like manually automating the fader to adjust the volume of a part to even it out, which is what I assume using a compressor in this case is for.

3) When working with samples, especially those of a consistent velocity (specifically kick hits), what's the purpose of compressing them if you don't need to equalize the level? I mean, compression by definition is a dynamics control, so if the track you're applying it to has no dynamics, then what's the point? The only reason I can imagine is if you've got a compressor that has a certain kind of coloration that you like, so really, you're not even using it for its compression, just it's affect on the sound.

Those are the three that immediately come to mind as having constantly baffled me. I understand (and more importantly, can notice) the affects of varied attack and release times when compressing the master bus, but it's the individual track compression that's always kinda thrown me off.

Thanks a ton guys!

 

[gorath23]

I would also like a Compression Sticky, as I know what the various knobs signify but often I just fiddle until it sounds ok, which is fine, but I'm sure I could get better results being a bit more objective about it.

 

[AudioGeekZine]

One of the things that really helped me was an interview with Charles Dye, where he said he uses compression not only for controlling dynamics but also altering the envelope of a sound. I'd never thought about it like that but it makes a ton of sense.

soooo... if you want to add punch to say a kick drum, you want to slow the attack of the comp just enough to let the original transient through, and the compression will bring up the decay of the kick to a more constant level.

Metaltastic it might help you to route some stuff in a way that you've got an instrument going through a compressor and being recorded onto another track, as you mess around with the compression ratio, attack and release you can visually see what is happening to the sound.

 

[aramism]

i agree. a compression sticky would be helpful

 

[TeamOmega]

This definitely needs to be sticky.

it might help you to route some stuff in a way that you've got an instrument going through a compressor and being recorded onto another track, as you mess around with the compression ratio, attack and release you can visually see what is happening to the sound.

good idea! don't know why i didn't think of that before

 

[hogan666]

Word!

I'm always fiddle around and really don't know what I'm doing.

Make it sticky

 

[Metaltastic]

Haha, well, preferably made a sticky after we get some answers, but your "record to another track while futzing with the compressor in real time" suggestion is pretty nifty AGZ, thanks! About the envelope suggestion though, I'm still a little confused - since all a compressor does is decrease the volume of things that go above its set threshold, how would it increase the volume of the things under it? (in this case, the decay/release of the kick hit) If you're referring to using the make-up gain fader, as I understand it, that fader applies to everything equally, so I'd think it'd be no different than just turning up the track volume fader (and thus would bring up both the transient and the decay/release, not just the latter)...

 

[jhrv]

James Murphy, LSD Studio, Oz. Where are you guys? We need some answers here!

 

[matt youwin]

Haha, well, preferably made a sticky after we get some answers, but your "record to another track while futzing with the compressor in real time" suggestion is pretty nifty AGZ, thanks! About the envelope suggestion though, I'm still a little confused - since all a compressor does is decrease the volume of things that go above its set threshold, how would it increase the volume of the things under it? (in this case, the decay/release of the kick hit) If you're referring to using the make-up gain fader, as I understand it, that fader applies to everything equally, so I'd think it'd be no different than just turning up the track volume fader (and thus would bring up both the transient and the decay/release, not just the latter)...

It is applied to everything equally, but only after anything above the threshold has been compressed. For example, say you're getting 3db of compression, so you set the make-up gain to +3db. The transient (and everything above the threshold) essentially stays the same volume (-3db compression, +3db makeup gain), while everything else (the tail of the kick etc) is given a 3 db boost from the makeup gain. This gives it more 'body', and can result in a punchier kick sound when applied correctly

Hopefully this pic helps explain (I tried to find a pic of a single hit to make it obvious but couldn't, and I'm at work, so can't screen capture from a DAW sorry)

Can you see how the 'body' of the waveform has been increased in amplitude, but the transients (above the threshold) haven't?

 

[PostMortem1666]

I am starting to understand this better. Thanks to Metaltastic for starting this thread. Release is what confuses me. I always change it but I never hear an audible difference. Can someone help explain this?

 

[colonel kurtz]

the release is also the hardest for me to hear the effect of...basically, it's the amount of time the compressor takes to stop acting after the signal jumps back below the threshold

if you want things to "snap" back, go for a quick release...if you want a smooth transition into the un-compressed signal, make it longer

 

[aramism]

if anyone uses the waves api comp. i never got how to set it to auto release. it has the "variable" release section right next to the regular release section but there are still set numbers. i think maybe the variable doesn't refer to auto release. it is a more detailed set of values for fine tuning i guess im not sure. anyone chime in on this?

 

[AudioGeekZine]

release is the time it takes for the compressor to stop compressing after the level has dropped below the threshold. A long release will continue to compress regardless of the input. You ideally want to set the release so is timed to end just before the next transient.
It's not the most audible thing in the world, in fact many compressors (LA2A and optical compressors) don't have attack and release controls, some have an auto release control which adjusts depending on whats going through the compressor.


Check out Stillwell/Shwa Sculpto to see the waveform change. loop a kick drum or snare or whatever and mess around with the controls on a compressor in line before it.

 

[alexrookie]

to be honest, i don't like the way most automatic release times work.
it's not precise.
one of the worst is the waves ssl bus compressor with automatic release.

to hear what release time is right for your signal try extreme settings (threshold,ratio) and you'll hear how the comp lets go.

most of the time i set the release of my compressors to the tempo of the song.
i open a delay plug in that tells me the ms for the bpm and usually it is the 1/8 th note.

for example: a song in 170 bpm - 1/8th note = 88 ms

just my 2 cents

 

[Morgan C]

@Matt youwin
Why does the transient stay at the same volume after makeup gain? I thought that apart from the transient, everything else gets reduced in volume, but the transient stays full (not -3db as you said) and then by raising the makeup gain you limited the transient..

Also, another question, when parallel compressing, do you guys usually use 0 attack time? I find if I use anything other than 0 then the wierd transient coupled with the smashing leads to crazy results when the drum is hit soft (ie ghost notes or a crescendo).

Oh, and when compressing kicks, I'll set the attack at 30ms maybe even 40ms but it always ends up cutting out the lowend. Do you guys use multiband compression, or slower attack times or am I missing something?

 

[aramism]

not sure it those last 3 replies were directed at me but i know how release works and what it does i was tring to figure out if the api 2500 compressor has an auto-release feature.

 

[AudioGeekZine]

I don't think those were directed at you, you posted while I was still typing mine.

I don't have the api plugs but from looking at the screenshot I figure: release knob is measured in seconds, and when you turn it fully to the right, you switch over to the other knob which has even shorter times. doesn't really make sense to me, but its copying a classic hardware design

 

[Metaltastic]

It is applied to everything equally, but only after anything above the threshold has been compressed. For example, say you're getting 3db of compression, so you set the make-up gain to +3db. The transient (and everything above the threshold) essentially stays the same volume (-3db compression, +3db makeup gain), while everything else (the tail of the kick etc) is given a 3 db boost from the makeup gain. This gives it more 'body', and can result in a punchier kick sound when applied correctly

Hopefully this pic helps explain (I tried to find a pic of a single hit to make it obvious but couldn't, and I'm at work, so can't screen capture from a DAW sorry)

Can you see how the 'body' of the waveform has been increased in amplitude, but the transients (above the threshold) haven't?

Thanks so much dude, that helps immensely! I understood it from your description, and the pics only solidify my certainty, so all the better! I always thought that in the digital world, turning up the make-up gain was no different than raising the track fader, but I'm glad to see I was wrong (cuz its much more useful this way )

And the suggestion of cranking up the threshold/ratio to hear the effects of attack and esp. release times is smart, I'll definitely give that a go!

 

[Metaltastic]

@Matt youwin
Why does the transient stay at the same volume after makeup gain? I thought that apart from the transient, everything else gets reduced in volume, but the transient stays full (not -3db as you said) and then by raising the makeup gain you limited the transient..

Well as I've just learned, the make-up gain only raises the volume of what the compressor is being applied to, and since your setting the attack time high enough that the transient isn't compressed, it therefore isn't raised, but still triggers the compressor to act on the decay/release.

1) When trying to "smash" something (usually vocals/bass, as well as any parallel compression), wouldn't one always want to use the fastest attack possible? The way I see it is you're trying to even out the volume, so even letting a little transient through before clamping down seems like it would defeat the purpose.

2) By the same token, when trying to "smash" something, why wouldn't one always want the fastest release? To me, that seems like it'd be the most transparent, cuz I'd imagine it'd be like manually automating the fader to adjust the volume of a part to even it out, which is what I assume using a compressor in this case is for.

Also, another question, when parallel compressing, do you guys usually use 0 attack time? I find if I use anything other than 0 then the wierd transient coupled with the smashing leads to crazy results when the drum is hit soft (ie ghost notes or a crescendo).

Oh, and when compressing kicks, I'll set the attack at 30ms maybe even 40ms but it always ends up cutting out the lowend. Do you guys use multiband compression, or slower attack times or am I missing something?

Anybody have any thoughts on these? This thread is off to a great start so far, keep up the advice! (and the questions, people are more likely to post if they've got something specific to respond to, after all!)

 

[TeamOmega]

Also, another question, when parallel compressing, do you guys usually use 0 attack time? I find if I use anything other than 0 then the wierd transient coupled with the smashing leads to crazy results when the drum is hit soft (ie ghost notes or a crescendo).

Oh, and when compressing kicks, I'll set the attack at 30ms maybe even 40ms but it always ends up cutting out the lowend. Do you guys use multiband compression, or slower attack times or am I missing something?

When i use parallel compression i use the same attack times (usually the longest attack possible), but have the ratio maxed out for the parallel track. i definitely like the results i get like this and don't get any weird sounds