Not sure how to use a compressor without squashing the life out of your mix? Set the threshold so only the loudest peaks trigger it, pick a modest ratio, then tune attack and release by ear.
This guide is part of our wider look at music production.
| Control | Typical value from the sources |
|---|---|
| Threshold example | -10 dB: only peaks above that level are compressed |
| Ratio example | 2:1: a signal 10 dB over the threshold comes out 5 dB over |
| Fast attack times | 20 to 800 microseconds |
| Slow attack times | 10 to 100 ms |
| Release times | 40-60 ms up to 2-5 seconds |
These figures come from Universal Audio’s compression basics and Mastering.com’s compressor guide. Ranges vary by unit and plugin, so check the sources and your own compressor’s manual before you rely on them.
What a compressor actually does
A compressor is an automatic volume control. When the signal gets louder than a level you choose, it turns the signal down; when the signal is quieter, it leaves it alone.
The result is a smaller gap between the loud and quiet parts, which is what people mean by dynamic range. A vocal that jumps out on some words and disappears on others becomes steadier and easier to place in a mix.
Compression is not only about control. Many compressors, in hardware and software, also have a signature sound that adds colour and tone, which is why engineers choose particular models for particular jobs.
Almost every compressor, whatever its look, is built from the same handful of controls:
- Threshold: where compression starts.
- Ratio: how hard it pushes the signal down.
- Attack: how fast it reacts.
- Release: how fast it lets go.
- Makeup gain: how much you turn the result back up.
Threshold and ratio: how much and how hard
The threshold sets the level at which the compression effect is engaged. With a hard knee, compression begins above the threshold: at -10 dB, peaks exceeding that level trigger gain reduction. A soft knee introduces compression gradually around the threshold.
Set it too high and nothing happens. Set it too low and the compressor works on everything, flattening the performance.
The ratio decides how much of the overshoot is removed. In Mastering.com’s example, a vocal goes over the threshold by 10 dB with the ratio at 2:1, so instead of getting 10 dB louder, the vocal now gets 5 dB louder.
At a ratio of 4:1, the overshoot is reduced by a factor of four. Higher ratios are firmer, and a very high ratio starts to behave like a limiter, which stops peaks rather than shaping them.
A sensible habit for beginners is to start with a gentle ratio and increase it only when the gentle setting cannot control the part. Heavy settings are easy to reach for and hard to undo once you have got used to the sound.
Hard knee or soft knee
Some compressors include a knee control. A soft knee allows for a smoother and more gradual compression than a hard knee, so the effect fades in as the signal approaches the threshold instead of switching on abruptly.
Soft knees suit vocals and full mixes where you want the compressor to go unnoticed. Hard knees suit drums and other sources where you want a more obvious grip.
Attack and release: when it grabs and lets go
Attack is the time it takes for the signal to become fully compressed after exceeding the threshold. Universal Audio gives example attack ranges of 20–800 microseconds for fast settings and 10–100 ms for slow settings, with variation between compressors.
A slower attack lets the first hit of a drum or pluck through before the compressor clamps down, which keeps punch. A faster attack catches that transient and softens it.
Very fast attacks can also cause trouble with low frequencies. A 100 Hz cycle lasts 10 ms, so a 1 ms attack has time to alter the waveform, which can generate distortion, according to Universal Audio.
Release is the opposite: how long the compressor takes to stop working once the signal falls back under the threshold. Universal Audio lists release settings spanning 40–60 ms at the short end and 2–5 seconds at the long end, depending on the compressor.
Following Universal Audio’s advice, shorten the release while listening for unwanted level fluctuations. Strong kick or bass hits can make background noise audibly rise and fall as gain reduction recovers.
A step-by-step way to set a compressor
Work in a fixed order so you always know which control caused a change. Loop a representative section of the track, including its loudest part, and follow these steps.
- Start with a low-to-moderate ratio such as 2:1 and a medium attack and release.
- Lower the threshold until the gain reduction meter moves on the loudest notes or words.
- Adjust the attack. Slower keeps the punch; faster tames the transient.
- Adjust the release so the meter returns to rest before the next note, without audible pumping.
- Add makeup gain until the compressed and bypassed versions sit at the same loudness.
- Toggle bypass and ask whether the part sits better, not whether it sounds louder.
Step five matters more than it looks. Louder usually sounds better, so unless you match levels, your ears will vote for the compressed version even when it is worse.
Use the meter as a guide and your ears as the judge. If you can clearly hear the compressor working on a track where you wanted transparency, back off the threshold or the ratio.
Common mistakes and where to go next
Most early compression problems come from the same few habits:
- Compressing everything by default, even parts that already sit well.
- Using fast attacks on sources where you wanted punch.
- Setting release so short that the track pumps or breathes.
- Skipping level matching and judging by loudness.
- Using compression to fix tone problems that belong to equalisation.
That last point is worth taking seriously. If a vocal sounds boxy or a bass is muddy, a compressor will not cure it, and learning how to use eq will do more for you.
Once the basics feel natural, you can go further and use the compressor’s detector in creative ways. Our guide to sidechain compression shows how another signal can trigger the gain reduction, for example ducking a bass under a kick.
Finally, practise on one instrument at a time. Take a single vocal or drum loop, set the compressor extreme on purpose so you can hear each control clearly, and then back it off to something musical. That exercise teaches more about attack and release than any chart of numbers.
Frequently asked questions
What is the best compressor setting for vocals?
Show answer
There is no single best setting, because it depends on the singer and the song. A gentle ratio such as 2:1 with a medium attack and release is a reasonable starting point; then lower the threshold until the loudest words are controlled.
Should I set attack fast or slow?
Show answer
Slow attacks let transients through and keep punch, while fast attacks tame them. Choose based on whether the source needs its initial hit preserved or smoothed.
Why does my compressed track sound like it is pumping?
Show answer
Usually the release is too short, so the compressor cycles on and off with the signal. Lengthen the release until the gain reduction meter settles between notes.
Do I need makeup gain?
Show answer
Yes, in most cases. Compression turns peaks down, so you raise the overall level afterwards and compare against bypass at matched loudness.
