Class MultibandCompressor

A 3-band compressor, built from native Web Audio nodes, so it does not require WebAssembly. The signal is split into a low, mid and high band, every band is compressed separately, and the bands are summed again. This controls, for example, boomy lows without pumping the rest of the mix.

Extends Effector.

Signal flow

input -+-> LR4 lowpass (low x-over) -> allpass (high x-over) -> compressor -> makeup -+
       |                                                                              |
       +-> LR4 highpass (low x-over) -+-> LR4 lowpass (high x-over)  -> compressor -> makeup -+-> output gain -> output
                                      +-> LR4 highpass (high x-over) -> compressor -> makeup -+

• The crossovers are 4th-order Linkwitz-Riley filters (two cascaded Butterworth biquads).
• The low band passes through an allpass at the high crossover, so all three bands have the same phase. Without compression, the bands sum back to a perfectly flat response.
• Every native DynamicsCompressorNode adds an automatic makeup gain (about +8.5 dB per band at the default settings). MultibandCompressor undoes that per band, so makeupGain is the only gain that is added and quiet signals pass at their original level.

Example

import { MultibandCompressor } from "@fluex/fluexgl-dsp";

const mbc = new MultibandCompressor({
    lowCrossover: 150,
    highCrossover: 3000,
    low: { threshold: -30, ratio: 4 },   // tame the low end
    mid: { threshold: -20, ratio: 2 },
    high: { threshold: -24, ratio: 3, makeupGain: 2 }
});

master.attachEffect(mbc);

// Metering
setInterval(() => console.log(mbc.reduction), 250); // { low: -4.2, mid: -0.8, high: -1.5 }

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Constructor

new MultibandCompressor(options?: Partial<MultibandCompressorOptions>): MultibandCompressor;

Arguments

• options?: Partial<MultibandCompressorOptions> Every field is optional. Band fields fall back to the band defaults below.

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Properties

lowCrossover: number

Crossover between the low and mid band (Hz). Defaults to 200.

highCrossover: number

Crossover between the mid and high band (Hz). Always at least 1.5x lowCrossover. Defaults to 2500.

outputGain: number

Gain (dB) after the bands are summed, between -24 and 24. Defaults to 0.

bands: Record<"low" | "mid" | "high", MultibandCompressorBandOptions>

The settings per band. Change them with setBand(). Defaults:

| Band | threshold | knee | ratio | attack | release | makeupGain | |---|---|---|---|---|---|---| | low | -24 dB | 6 dB | 3 | 0.010 s | 0.20 s | 0 dB | | mid | -24 dB | 6 dB | 3 | 0.005 s | 0.15 s | 0 dB | | high | -24 dB | 6 dB | 3 | 0.002 s | 0.10 s | 0 dB |

inputGainNode: GainNode | null / outputGainNode: GainNode | null

Input and output nodes. null until attached.

label and name default to "MultibandCompressor".

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Methods

initializeOnAttachment(context: AudioContext): Promise<void>

Creates the crossover filters, compressors and gain nodes.

returnOptionsAsObject(): MultibandCompressorOptions

Returns a snapshot of the crossovers, bands and output gain.

setBand(name: "low" | "mid" | "high", options: Partial<MultibandCompressorBandOptions>): boolean

Changes the settings of one band. Only the given fields change, with a 10 ms ramp. See MultibandCompressorBandOptions for the ranges.

Arguments

• name, options

Returns

• boolean - true when applied to the audio nodes, false when the effect is not attached yet (the values are used on attachment).

setCrossovers(lowCrossover: number, highCrossover: number): boolean

Moves both crossovers (Hz). The low crossover is clamped between 20 Hz and 13.3 kHz; the high crossover between 1.5x the low crossover and 20 kHz.

Arguments

• lowCrossover: number, highCrossover: number

Returns

• boolean - true when applied to the filters, false when the effect is not attached yet.

setLowCrossover(frequency: number): boolean / setHighCrossover(frequency: number): boolean

Moves one crossover. Same rules as setCrossovers().

setOutputGain(outputGain: number): boolean

Sets the gain after the bands are summed (dB).

Arguments

• outputGain: number

Returns

• boolean - true when applied, false when the effect is not attached yet.

Getters and setters

get reduction(): { low: number, mid: number, high: number }

Current gain reduction per band in dB (0 or negative). Useful for metering.

get inputNode(): AudioNode | null / get outputNode(): AudioNode | null

Return inputGainNode and outputGainNode.

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Events

MultibandCompressor does not use an AudioWorklet processor, so it does not dispatch processor events.