# Compressor

**In the desktop app.** Compressor is a device of the desktop app, arriving in its beta; the web studio does not have it. The examples on this page are made with a reference version of the effect, applied to sound from the studio's engine: they show what each control does, and the device itself may differ a little in character.

## What it is for {#compressor}

A **compressor** turns a sound down whenever it gets loud, by itself, many times a second. Once the loud moments are held back, the whole part can be turned up, so the quiet moments are heard and nothing jumps out. The part sits at one steady level in the mix instead of appearing and disappearing.

Reach for it when a vocal, bass or drum part is uneven: some notes are lost, others are too much, and no position of the fader is right for all of them. [Dynamics](/manual/sound-in-ten-ideas#dynamics) is the idea behind it.

<AudioSet title="Drums played unevenly" hint="Both at the same overall loudness. Listen to the quiet hits." :examples="[['compressor-before', 'As played'], ['compressor-after', 'Compressed']]" />

It is easy to overdo: a sound compressed too hard is flat and tiring, with no difference left between soft and hard playing. If you cannot hear what the compressor is doing, it is often already doing enough.

## Threshold {#compressor-threshold}

The level above which the compressor starts turning down, in decibels. Everything quieter passes untouched. Lower the threshold and more of the sound is caught; raise it and only the loudest peaks are.

<AudioSet title="Threshold" :examples="[['compressor-threshold-high', 'High: only the hardest hits are caught'], ['compressor-threshold-low', 'Low: everything is held']]" />

## Ratio {#compressor-ratio}

How firmly the sound is held once it is over the threshold. At 2:1, a sound that goes 2 dB over comes out 1 dB over: gentle, hard to notice. At 10:1 almost nothing gets past, and the result is tight and flat.

<AudioSet title="Ratio" :examples="[['compressor-ratio-gentle', '2:1'], ['compressor-ratio-strong', '12:1']]" />

## Attack {#compressor-attack}

How quickly the compressor reacts when the sound gets loud. A fast attack catches the very start of each hit and makes it softer and rounder. A slow attack lets the start through before holding the rest, which keeps the punch and can even add to it.

<AudioSet title="Attack" :examples="[['compressor-attack-fast', 'Fast: the hit itself is softened'], ['compressor-attack-slow', 'Slow: the hit punches through']]" />

## Release {#compressor-release}

How quickly the compressor lets go when the sound gets quiet again. A fast release brings the level back up between hits, which makes a part sound louder and more excited, and at the extreme makes it audibly pump. A slow release keeps the level down longer, which is smoother and calmer.

<AudioSet title="Release" :examples="[['compressor-release-fast', 'Fast: breathes between the hits'], ['compressor-release-slow', 'Slow: stays held']]" />

## Gain {#compressor-gain}

Level added after the compression. Holding back the loud moments makes the whole part quieter, and Gain brings it back to where it was. Set it so that the sound is equally loud with the compressor on and off; only then can you tell whether it is better or just louder.

## Mix {#compressor-mix}

The share of compressed sound in the result. Below 100 %, the untouched sound is blended back in: you keep the life of the original and gain the body of the compressed one. See [Mix](/manual/devices#devices-mix).

## Listen to {#compressor-listen}

Normally a compressor reacts to the sound that passes through it. **Listen to** makes it react to another track instead: choose a track from the menu, and this one is held back whenever that track is loud, not when it is loud itself. Other studios call this a sidechain and ask you to route a signal by hand; here it is one menu.

It is how a pad makes room for a vocal, or music dips under a spoken voice. For the plain case of one track stepping aside for another, the [Ducker](/manual/ducker) does the same with two knobs.

Set to **Nothing**, the compressor listens to its own track. If the track it listened to is deleted, the menu says **A removed track** and the compressor goes back to its own sound until you choose another.

## Listen above {#compressor-listen-low-cut}

Under **More**. The compressor stops listening to the lowest notes, from 20 to 500 Hz, while still working on all of the sound. Without it a big bass or kick sets the whole track pumping; with it the compressor answers the voice or the guitar instead. At its lowest it is off and the compressor hears everything.

## The reduction meter {#compressor-reduction}

The meter shows how much the compressor is turning the sound down at each moment, in decibels. It is the quickest way to know what the device is doing: a needle that barely moves means the threshold is above the sound; one that never returns to zero means the sound is being held all the time. For most parts, moving between 3 and 6 dB on the loud moments is plenty.