A compressor turns down the parts of a sound that are louder than a level you choose, which shrinks the gap between the loudest and quietest moments. The part then sits at a steadier level, and once you add a makeup gain boost it can read as fuller and more controlled. The controls decide how much it turns down and how fast.
The controls are the same on almost every compressor, hardware or plugin: threshold, ratio, attack, release, knee and makeup gain, read against a gain reduction meter. None of this is tied to one product.
A compressor turns down the parts of a sound that are louder than a level you set, so the gap between the loudest and quietest moments gets smaller. That gap is the dynamic range, and reducing it makes a part sit at a steadier, more even level instead of jumping around.
It works by watching the incoming signal against a level called the threshold. While the signal stays under the threshold, nothing happens and the sound passes through untouched. The moment it goes over, the compressor reduces its gain by an amount set by the ratio, so the peaks that used to leap out are pulled back toward the rest of the part. Because the loud moments are now closer to the quiet ones, you can lift the whole part with makeup gain, and it reads as louder and fuller without the peaks clipping.
This matters because most parts you record move around in level more than a mix can comfortably hold. A singer leans into the mic and backs off, a bass player picks harder on some notes, one drum hit lands harder than the one before. Compression tames that movement so every word and note stays audible in its place, which is why it is one of the most used tools in mixing.
A compressor does not add anything to the tone on its own. It is an automatic, very fast volume control. Everything it is known for, punch, glue and sustain, comes from how quickly it turns the level down and how quickly it comes back up, which you set with the attack and release.
These are the four main controls. Threshold sets the level where compression begins, ratio sets how hard the signal is turned down once it is over that level, and attack and release set how fast the compressor clamps down and how fast it lets go. Two more, knee and makeup gain, shape and rebalance the result. Here is what each one does and a sensible place to start.
| Control | What it does | A place to start |
|---|---|---|
| Threshold | The level above which the compressor starts turning the signal down. Anything below it passes through untouched. A lower threshold catches more of the part. | Lower it until the loud parts show a few dB of gain reduction |
| Ratio | How hard it turns down whatever is over the threshold. 4:1 means for every 4 dB over the threshold, only 1 dB comes out. Higher ratios squeeze harder; very high ratios act as a limiter. | 2:1 to 4:1 for general use |
| Attack | How quickly it clamps down once the signal crosses the threshold. A fast attack catches the initial hit; a slow attack lets that hit through and compresses the body behind it. | 10 to 30 ms, faster to tame sharp transients |
| Release | How quickly it stops reducing gain once the signal drops back under the threshold. Too fast can pump; too slow stays clamped between notes. | 100 to 250 ms, or an auto setting |
| Knee | How gradually the ratio comes in around the threshold. A hard knee applies the full ratio the instant the threshold is crossed; a soft knee eases it in for a gentler, less obvious effect. | Soft knee for a transparent sound |
| Makeup gain | A level boost after compression to replace the volume lost by turning the peaks down, so the compressed part matches or beats the original loudness. | Match the bypassed level so you compare fairly |
| Gain reduction meter | Shows how many dB the compressor is turning the signal down at any moment. This is how you see it working. | A few dB on most single tracks |
Attack and release are what give a compressor its feel. A slow attack lets the initial hit of a sound, the transient, pass through before the compressor grabs it, so a snare or a plucked note keeps its punch and only the tail afterward is turned down. A fast attack catches that hit as well, which controls the part tightly but can dull the punch.
Release decides how the compressor recovers. Too fast and you can hear it turning the level up and down between hits, a pumping or breathing sound. Too slow and it stays clamped down and never fully recovers between notes. Somewhere in the middle, or an auto release, follows the music without drawing attention to itself.
Reach for a compressor when a part is too uneven to sit still in the mix, when you want a group of sounds to feel like one, or when you want to shape the punch or sustain of something. In short, whenever you need to control or reshape dynamics. The common jobs:
A safe way in is a ratio around 2:1 to 4:1, the threshold lowered until the loudest parts show a few dB on the gain reduction meter, and a medium attack and release that you then adjust by ear. Set the makeup gain so the compressed part is the same loudness as the bypassed one, so you are judging the compression itself and not just a jump in level.
A sidechain compressor listens to one signal to decide how much to turn down another. The common example is a kick drum feeding the compressor on a bass or a pad, so the bass dips each time the kick lands and then recovers, clearing space for the low end. Pushed harder, that same trick is the pumping, breathing effect behind a lot of dance music.
Use the least amount that fixes the problem, keep an eye on the gain reduction meter, and always compare against the bypassed sound at a matched level. If the part sounds flat or lifeless, or you can hear it pumping in time with the music, you have gone too far.
The trap is that compression usually sounds better at first for the wrong reason. Turning the peaks down and adding makeup gain makes the part louder, and louder almost always sounds better in a quick comparison, so it is easy to talk yourself into using more than you need. Before you decide, turn the compressed version down to match the bypassed loudness, then switch between them. Often the lighter setting wins.
Watch the meter, not just your ears. A few dB of gain reduction is plenty on most single tracks, and one to three dB is common on a bus. If the meter is showing ten or fifteen dB, the part will usually sound squashed, with its natural rise and fall flattened out.
Pumping is the other tell. When the ratio is too high or the release too fast, the compressor turns the level up and down audibly between hits and the whole part seems to breathe. Unless that is the effect you are after, ease the ratio back, slow the release, or raise the threshold so it acts less often. And if a part still is not controlled enough with gentle settings, two light compressors in series usually sound more natural than one working very hard.
Louder is not the same as better. Because a compressor with makeup gain makes a part louder, it can seem to improve a sound it is actually flattening. Match the levels before you judge, aim for a few dB of gain reduction on most sources, and reach for compression to solve a specific problem rather than putting it on everything out of habit.
Compression is a mixing step. It only matters once you have parts worth mixing, and writing and recording those is the harder job. The settings on this page are simple to learn; having something to point them at is the work.
The Collection is our three instruments together, ARGISH, SILT and REHEAT, with three separate licence keys. This page is about the mixing step, but you need parts to mix first: ARGISH is a self-playing drone synth, SILT is a tape-loop instrument, and REHEAT writes acid lines. Make the parts with them, then compress them to sit together in one mix, and whatever you make is yours to release. Every one ships as an Audio Unit, a VST3, an AAX for Pro Tools and a standalone app on macOS, signed and notarized, and a VST3 on Windows.
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