# Filter · zvuk

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

Biquad filter as a bus FX insert. Lowpass for muffles, highpass for radios, bandpass for telephone, peaking for EQ.

FX

# Filter

Biquad filter as a bus FX insert. Lowpass for muffles, highpass for radios, bandpass for telephone, peaking for EQ.

Everything muffles when the player goes underwater, and the cheapest convincing version of that is one filter on one bus.

A [`Filter`](/api/Filter/) is a single `BiquadFilterNode` wrapped in the FX-insert contract. Pick a type, a frequency and a Q. Drive any of them from a [Parameter](/concepts/parameter/) when you want the transition rather than the state.

## API surface

Filter + FilterConfig ts

```
class Filter implements FxInsert {
  readonly input: GainNode;
  readonly output: GainNode;
  bypassed: boolean;

  setType(t: FilterKind): void;
  setFrequency(hz: number): void;
  setQ(q: number): void;
  setGain(db: number): void;   // peaking gain, live
  dispose(): void;
}

type FilterKind = 'lowpass' | 'highpass' | 'bandpass' | 'notch' | 'peaking' | 'allpass';

interface FilterConfig {
  type?: FilterKind;
  frequency?: number;                 // Hz
  q?: number;
  gain?: number;                      // dB — peaking only
}
```

## Live demo

Type, frequency, Q. Try lowpass at 400 Hz with high Q for a wah.

Use your own sound

bus outputidle

type

frequency (Hz)1200

Q1.00

Unlock & start stream

## Recipes

### Insert + live tweak

ts ts

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

const fx = new Filter(engine.context, {
  type: 'lowpass',
  frequency: 800,
  q: 1.2,
});
engine.bus('music').addFx(fx);

// Live sweep
fx.setFrequency(2000);
fx.setQ(0.7);
```

### "Underwater" sweep from a Parameter

ts ts

```
// Sweep a filter from a Parameter for "underwater" / "muffled" effects.
const muffle = engine.parameter('muffle', 0);
muffle.bindTo((v) => fx.setFrequency(v), { from: 20000, to: 400, curve: 'easeIn' });

muffle.set(1);   // fully underwater
```

## Common starting points

Effect

Type

Frequency

Q

Muffled / underwater

lowpass

400–800 Hz

1

Tinny radio / phone

bandpass

1500 Hz

2

Subwoofer cut

highpass

120 Hz

1

De-hiss

lowpass

10 kHz

0.7

Wah

bandpass

swept

4–8

## Pitfalls

Don't push Q to extremes.

Q above 10 starts ringing. On music, that's a feedback howl. Stay under 5 unless you're sweeping for a deliberate effect.

## Related

-   [FX index](/fx/)
-   [Parameter](/concepts/parameter/) — drive freq from a knob.