biquad-coeffs-webaudio-v1

WebAudio formulae for audio EQ biquad filter coefficients

• https://www.w3.org/TR/webaudio/

Installation

$ npm install --save biquad-coeffs-webaudio-v1

API

• [filterType](freq, q, gain): number[]
  • filterType: string
    • "lowpass"
    • "highpass"
    • "bandpass"
    • "notch"
    • "allpass"
    • "peaking"
    • "lowshelf"
    • "highshelf"
  • freq: number filter cutoff or center frequency
    • This parameter should be normalized (0..1).
    • normalizedFrequency = frequency / sampleRate
  • q: number filter Q (resonance)
    • This parameter is NOT used by "lowshelf" or "highshelf".
  • gain: number filter gain
    • This parameter is used by "peaking", "lowshelf" or "highshelf".
  • returns coeffs [ b0, b1, b2, a1, a2 ] (a0 = 1)

Usage

DSP

const coeffs = require("biquad-coeffs-webaudio-v1");

const [ b0, b1, b2, a1, a2 ] = coeffs.lowpass(1200/44100, 6);
const signal = new Float32Array(2048).map(Math.random);

let x0, x1 = 0, x2 = 0;
let y0, y1 = 0, y2 = 0;

for (let i = 0; i < signal.length; i++) {
  x0 = signal[i];
  y0 = (b0 * x0) + (b1 * x1) + (b2 * x2) - (a1 * y1) - (a2 * y2);

  signal[i] = y0;

  x2 = x1;
  x1 = x0;
  y2 = y1;
  y1 = y0;
}

Web Audio API

const coeffs = require("biquad-coeffs-webaudio-v1");

const [ b0, b1, b2, a1, a2 ] = coeffs.lowpass(1200/audioContext.sampleRate, 6);
const audioContext = new AudioContext();
const oscillator = audioContext.createOscillator();
const filter = audioContext.createIIRFilter([ b0, b1, b2 ], [ 1, a1, a2 ]);

oscillator.type = "sawtooth";
oscillator.frequency.value = 880;
oscillator.start(audioContext.currentTime);
oscillator.stop(audioContext.currentTime + 2);
oscillator.connect(filter);

filter.connect(audioContext.destination);

License

MIT