# Compressor · zvuk

zvuk v1.14.1 · MIT · https://zvuk.schmooky.dev/fx/compressor/

Dynamic range compression as a bus FX insert. Wraps DynamicsCompressorNode and makeup gain. Bypass is a graph swap, so it has no parameter latency.

FX

# Compressor

Dynamic range compression as a bus FX insert. Wraps DynamicsCompressorNode and makeup gain. Bypass is a graph swap, so it has no parameter latency.

One line of dialogue is a whisper and the next is a shout, and the player is on a phone at a bus stop. Compression is how you make both audible without making either wrong.

A [`Compressor`](/api/Compressor/) narrows the dynamic range of whatever passes through it. Use it on a voice bus to even out dialogue, on a music bus for glue, or on the master as a soft limiter at `ratio: 20` with a fast attack.

It is limiter-_like_ and not a brick wall. With a finite attack and no lookahead, transients still get through, so it is not a guarantee against clipping.

## API surface

Compressor + CompressorConfig ts

```
class Compressor implements FxInsert {
  readonly input: GainNode;
  readonly output: GainNode;

  bypassed: boolean;                  // graph-swap, not a parameter

  applyConfig(c: CompressorConfig): void;
  get reduction(): number;            // live gain reduction (negative dB)
  dispose(): void;
}

interface CompressorConfig {
  threshold?: number;                 // dB, default -24
  knee?:      number;                 // dB,   default 30
  ratio?:     number;                 // n:1,  default 12
  attack?:    number;                 // s,    default 0.003
  release?:   number;                 // s,    default 0.25
  makeupGain?: number;                // dB,   default 0
}
```

## Live demo

Five knobs and a live reduction meter. Toggle bypass to A/B against the dry signal. The meter drops to zero when bypassed.

Use your own sound

bus output (post-compressor)idle

gain reduction0.00 dB

threshold (dB)\-24

ratio6.0:1

attack (s)0.005

release (s)0.18

makeup (dB)6.0

engagedreset

Unlock & start fire

## Recipes

### Voice bus glue

ts ts

```
import { Compressor } from '@schmooky/zvuk';

const comp = new Compressor(engine.context, {
  threshold: -18,
  ratio: 4,
  attack: 0.005,
  release: 0.18,
  makeupGain: 6,
});

engine.bus('voice').addFx(comp);

// Live tweaks:
comp.applyConfig({ threshold: -22, ratio: 6 });
comp.bypassed = true;                 // a/b test
```

### Read live gain reduction

ts ts

```
setInterval(() => {
  console.log('reduction:', comp.reduction.toFixed(2), 'dB');
}, 33);
```

## Pitfalls

Don't compress music to mush.

Ratios above 8:1 on music sound pumpy. Reserve heavy ratios for voice or SFX glue. For music, sit between 2:1 and 4:1 with a soft knee.

Don't dial makeupGain to compensate fully.

Match the bypassed level by ear, not by math. The compressor is doing work; trust the meter, not the knob.

Don't put a Compressor on every bus.

Each bus's compressor is independent. Stacking them makes your mix breathe in unpredictable ways. Pick the bus where the dynamics actually matter.

## Related

-   [FX index](/fx/)
-   [Sidechain ducking](/guides/ducking/) covers Ducker, a compressor keyed from another bus.
-   [Bus](/concepts/bus/) is where FX inserts live.