The compressor attack is as important as the compressor ratio for determining how much your audio is compressed. Set this too slow and you won’t get any compression. Set the attack too quickly and you’ll completely remove the punchiness from your track. Let’s talk about the compressor attack and where you should set this to find the perfect balance for your track.
Compressor Attack Explained
As I mentioned in my audio compressor settings chart, the compressor attack determines how soon after the input volume of the track passes the threshold you set.
Once the threshold is met, compression begins after whatever attack time you set.
Set the attack to 500ms and it takes half a second before the compression kicks in. Set it to 1000ms and it takes a full second before compression starts.
Attack is measured in milliseconds. Given how quickly and dynamically sound moves, a SLOW attack can actually be 50ms or more.
A fast attack is typically characterized as a few milliseconds or less.
It should be mentioned that while the attack is the chief determiner in how quickly the compressor kicks in, it’s not the only one.
The compressor’s knee determines how strictly the threshold is enforced. With a hard knee, the threshold is strictly adhered to and the attack is all that determines when the compression starts.
With a softer knee, compression gradually begins as the signal approaches the threshold. As such, the compression begins earlier than you have the attack set to with a sort of combination between the attack time and slope of the knee.
Where to Set Compressor Attack
I mentioned in opening that setting your attack to be too quick, too instant, will remove the punchiness from your audio.
Punch is a mixing term used to describe that initial “hit” of a sound. This is also referred to as the transient of a sound.
Transients are what keep your mix lively and your listener engaged because they draw the ear.
When the attack is set too short and too fast, the compressor clamps down on those initial transients of the sound.
You need that little spike of the transients on the front end of those peaks for a split second before the compression engages and pulls the volume down according to the ratio.
A ratio of just a few milliseconds is actually slow enough on most tracks to keep that punch intact and audible while still getting the benefits of the compression.
Getting back to the question of where to set compressor attack, I’ve put together a number of tutorials on the most common instruments including vocals:
- Compressor Settings for Vocals
- How to Compress Bass Guitar
- Piano Compression Guide
- Compression on Acoustic Guitar
- Snare Compression
Generally an attack time of somewhere between 1-5ms works well for maintaining punch while getting the control and energy from the compression.
Remember that the knee affects the engage speed in a sense, so you should set these together to dial in the perfect attack speed.
Of course the best answer is to trust your ears.
If you find that there’s no change when you first hear the track play at any given peak, that means that you’ve got the attack set too fast/short and you’ve lost your transient.
Dial it back a millisecond or so and see if you can hear that initial punch before the signal quickly drops.
It’s a subtle difference, admittedly, but you get better at noticing it over time and will consequently get better at selecting the best attack time for your compressor on a track by track basis.
Incidentally if you ever notice that one of your tracks seems to be missing in the mix despite the volume, you might check the attack on your compression.
It may be set too quickly to the point where you’re losing the punch which is what helps that track assert itself and draw the listener’s attention in the mix.