biquad-coeffs-cookbook

Cookbook formulae for audio EQ biquad filter coefficients

Usage no npm install needed!

<script type="module">
  import biquadCoeffsCookbook from 'https://cdn.skypack.dev/biquad-coeffs-cookbook';
</script>

README

biquad-coeffs-cookbook

Build Status NPM Version License

Cookbook formulae for audio EQ biquad filter coefficients

Installation

$ npm install --save biquad-coeffs-cookbook

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) or slope
    • 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-cookbook");

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-cookbook");

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