Help with compression attack and release settings.

M

MILLSY5

New member
Hi guys,

I have read several resources on compression but i am struggling to get a grasp on the concept. I am a little confused about the attack and release settings on a compressor. I would be grateful if someone could take the time to help me on this one.

Lets say i have a compressor with the follwing settings. Attack 10ms and release 20ms and my input signal is above te threshold setting for 50ms.

Please could someone explain how long the compressor will be working for.

Is the following statement true:
As soon as the input signal reaches the threshold the compressor starts working but it takes 10ms for it to get from 0 gain reduction to the amount of gain reduction as set by the ratio control. As soon as the signal drops below the threshold the compressor will stop working but it will take 20ms for it to get from the ratio setting to 0 compression.


What would happen if the attack was 100ms?
Would the compressor never actually reach the gain reduction as set by the ratio control because the release would start half way through the attack phase, or would it still reach full compression after 100ms and then the release phase would start.

How does the hard and soft knee settings effect all this??

Thank you very much anyone who takes the time to explain this.

Keith
 
The attack setting tells the compressor when to act. So say you have a level thats goes above the floor you set (threshold), the attack setting tells the compressor "wait X ms before you start compressing". The release tells the compressor - "when the sound dips below the floor, keep compressing for X ms"...
Is that what you are looking for?
 
Think of a compressor as a sound smasher. It can smash lightly or massively but its gonna smash something.

Threshold - how soon do I get to smash. Can I start when the volume is low, or do I wait until it gets really loud. High threshold -24 means I can start even when the volume is low. Low threshold -2 means I have to wait until things get louder before I get to smash. If I just want to trim off the transient peaks I would go with a low threshold.

Attack - How soon after the threshold lets me start do I have to wait to smash.

Release - How long do I get to smash before I have to let go.

Ratio - How much smashing to the volume do I get to do. Light or heavy.

Gain - I smashed the sound but I need to hear the smashing result louder. So I get to turn the smashed sound up a little louder.

Compressors compress (low ratios) and they limit (high ratios).
They can be used to smash the whole frequency spectrum, a standard compressor, or they can be frequency specific, multi band compressors.

They can be used to control transient peaks i.e. sudden increases in volume or often used just for the way they color the sound.
 
Hard knee is basically agressive attack. Soft knee is easy attack. They look like this.

Hard Knee then Soft Knee.
 

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Does the knee setting also determine how quickly the release stage works? If not what does?

Thanks for your help your a diamond.

Keith
 
The knee is the is a rate of attack and release you apply to your track.

Say the compressor attack is set to very fast on a snare drum hit, with a hard knee you would hear the compression flatten the transient of the drum and compress the sound very aggressively. It would also release very quickly after the release time. Overall you would really hear the compressor working "pumping" is the term.

With a soft knee the rate of attack would be more gradual, depending on the angle of the knee. Release would also be more gradual.

Attack is the ms start time after the threshold says go. Knee is how fast the attack and release is applied i.e. sharply or more gradual - kind of like gentle or hard application of the compression.

Vocals generally get a soft knee so the compression is less apparent, bass guitars and kick drums tend to get hard knees in rock music where the pumping can be a desired effect. Once again this is in general; occasionally a hard compressed voice may be desirable. Its art and anything goes.
 
Your help has been invaluable, thank you.

I have one final question. If i had attack set to 120ms and the sound was only above the threshold for 60ms would the release start at 120ms or 60ms.

Thanks

Keith
 
Actually it depends on the design of the compressor.

If you mean that the sound is only 60ms long after the threshold is reached then the transient would come through and not fire up the compressor waiting for the attack at 120ms before starting, so release is irrelevant. However some designers will implement a limiter for these fast acting sounds and do a gentle control which you have no adjustment for. Sometimes this is that "transparency factor" of an expensive analog compressor. It could be designed to sound really smooth and handle sudden short bursts. Others may not be smooth and would sound coarse. You hear the term fast and slow for various older compressors, these may not even have adjustments for attack and release, they have fixed times.

On the other hand, a design which ignores or is maybe not fast enough to react could just sit there and clip or, at the very least, just pass the transient no compression activated. Alternatively if you are still above the threshold it could let the transient through but compress the sound as it fades off.


However, if your example, means that the 60ms is after attack has started, the answer is, it depends on what the release setting was for how long you wanted to compress the sound. Release might be 60 but a compressor can hold it out longer (desirable on bass notes) than the actual length of the sound. So, it would depend on the release setting.

Hope that was clear.
 
Thanks mate. Ive been reading and experimenting all day and i think with your help i've finally got it.

Cheers once again.

Keith
 
Middleman said:
The knee is the is a rate of attack and release you apply to your track.

Say the compressor attack is set to very fast on a snare drum hit, with a hard knee you would hear the compression flatten the transient of the drum and compress the sound very aggressively. It would also release very quickly after the release time. Overall you would really hear the compressor working "pumping" is the term.

With a soft knee the rate of attack would be more gradual, depending on the angle of the knee. Release would also be more gradual.

Attack is the ms start time after the threshold says go. Knee is how fast the attack and release is applied i.e. sharply or more gradual - kind of like gentle or hard application of the compression.
Click to expand...

There's a couple of statments in there that point to knee as being a function of time as opposed to it being the level it thakes to reach the full compression ratio. When the signal is within the range of the knee, the ratio is less, but attack and release times remain (-unless there's some connection between them...?
Wayne
 
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