Compressor

Shape category, instrument-level.

Reduces the loud parts so the quiet parts can come up with them. The instrument then sits at a steadier level in the mix.

Controls

Amount. How much compression is applied. Turned down it levels gently, turned up it flattens the dynamics hard.

Character. The compressor's personality, and it works as a pair with Amount. Tight reacts quickly and clamps down. Punchy lets the initial transient through before it acts, which is what keeps drums and bass feeling heavy rather than dulled. Auto times its own recovery, described below.

A little Amount with Tight is transparent levelling. A lot with Punchy makes a part feel louder without losing its attack. A lot with Tight squashes everything flat, which suits aggressive electronic sounds and makes acoustic instruments lifeless.

Advanced controls

The popup keeps three more controls behind Advanced, because most tracks never need them.

Attack. How quickly the compressor acts once the signal crosses the threshold. Shorter catches the transient, longer lets it through.

Release. How quickly it lets go again. Ignored when Character is set to Auto, which sets release for you.

Key HPF. Applies only when a sidechain key is selected. It removes low frequencies from the key signal before the detector sees them, so the compressor reacts to the kick's transient rather than to bass bleed.

Presets

Tight, Punchy, Glued, Transparent.

Auto release and glue

With Character set to Auto, the compressor times its own recovery: brief peaks let go quickly, sustained loud passages release slowly. That program-dependent movement is what mix engineers call glue, and it is why separate parts start to feel like one performance. It is the behaviour of a classic studio bus compressor, and it is what the Glued preset uses.

Glue is most useful on the whole mix. Add the Compressor to the master bus, pick Glued, and aim for only a little reduction. On the master the detector is stereo-linked, so both sides always move together and a loud sound on one side never pulls the stereo image toward the other.

Sidechain: ducking to another track

The settings popup has a Sidechain key dropdown. Pick another track and the compressor stops reacting to this track's own level. It ducks whenever the chosen track is loud instead.

The classic use is the kick-and-bass pump: set the bass track's sidechain key to the drum track, and every kick pushes the bass down for a moment before it springs back. That is the breathing groove behind house, trance and modern pop.

Picking a key switches the Compressor on. Amount still sets how deep the duck is, and Character still sets how fast it reacts, snappy with Tight and smoother with Punchy. Choose None to go back to a normal compressor. Several tracks can key off the same source, so bass and pads can both duck to the kick.

For a pump that hits the same shape every bar regardless of what the kick actually played, use Sidekick instead.

When to use it

Bass and drums almost always benefit. Piano and guitar need it when their dynamics are wide. Pads and strings usually do not need it at all.