The Myth of Compressor Attack Time

Compression is something we’ve talked about in-depth on this blog a number of times, but today I want to talk about one aspect of compression that’s REALLY misunderstood: Attack Time.

It sounds so simple, right? The typical definition that people give when asked about attack time is “it’s the time it takes for the compressor to kick in and start compressing once the signal crosses the threshold”. The fact is…that’s not even close to the truth.

If you think about that definition for a second, it’ll occur to you that it seems like the attack time is really just a glorified delay control. The signal comes in, it crosses a threshold, then…there’s a period of time when nothing happens…then the compression starts. That’s how we’ve always thought about it, but actually that’s not how it works at all.

Let’s start with the correct definition of attack time: the Attack time of a compressor is the time it takes the compressor to: apply 9dB* of gain reduction to a signal, whenever the signal is over the threshold AND increasing in gain.

Ok, let’s talk about exactly what that means. First, we need to realize that attack TIME is really more like attack RATE. Increasing the attack time doesn’t slow down how long it takes for the compressor to respond, it actually slows down the RATE at which the compressor applies gain reduction. It always responds instantly, but it “moves” slower.

Here’s a great analogy: imagine you’re at a red light in your car with your foot hovering over the gas pedal. When the light turns green (when the signal goes over the threshold) you hit the accelerator immediately, every time. With a fast attack, you slam your foot on the pedal and speed up quickly. With a slow attack, you press the pedal gently, and it takes longer to get up to speed.

Each time, the initial response is identical: you step on the accelerator as soon as the light turns green, and you start moving as soon as the light turns green. The compressor myth says that increasing attack means you’d wait longer to step on the pedal. The truth is that increasing attack means you’d press on the pedal more slowly.

To sum it all up: attack time is NOT a delay before when the compressor starts. Attack time IS how long it takes the compressor to fully apply 9dB of gain reduction once the signal crosses the threshold. It always starts applying gain reduction instantly no matter how long or short the attack time is.

I hope that clears up some of the confusion surrounding attack time!

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