iZotope Pro Audio Essentials: Compressor Attack
The initial burst of a signal is typically referred to as the transient. It’s the sharpest, or most impactful part of the signal that we hear.
A fast attack means the compressor reduces the transient, because it acts quickly. A slower attack time will preserve the shape of the transient, and the result is that the signature of the compressor may not be as obvious.
Let’s listen to some examples. First, a snare drum. You’ll hear it uncompressed, compressed with a fast attack, and then compressed with a slow attack. In the version with the fast attack, you’ll notice a significant change to the transient, or the impact of the sound.
[snare, without and with compression, fast attack]
When you listen to the slow attack, you’ll notice that some of the transient is restored, but you’ll still hear the sound of the compressor.
[snare, without and with compression, slow attack]
Now, let’s listen to a recording of a bass. First, you’ll hear an uncompressed version, then one with a fast attack, and one with a slow attack.
[bass guitar, without and with compression, adjusting attack]
Let’s also think about the amount of gain reduction that’s happening as a result of the changing attack time. If you make the attack shorter, you get a bit more gain reduction due to the fact that the compressor is working more quickly. When the attack time is longer, the compressor is missing the initial transient, and therefore, it’s not working as much of the time, so you get a little bit less gain reduction.
If you want to listen to the effect of the attack on a signal, set your compressor up so you have two to three dB of gain reduction, starting with a very fast attack time, even as fast as zero milliseconds, and gradually increase the attack time. Listen to the change in the transients, and notice the change in the amount of gain reduction.
With practice, you’ll figure out a good place for the attack time setting to suit your audio.