biquad-coeffs-maxmsp


> Max/MSP formulae for audio EQ biquad filter coefficients
> - https://docs.cycling74.com/max7/maxobject/filtergraph~

Installation

``
$ npm install --save biquad-coeffs-maxmsp
`

API


- filterType: number[]
- filterType: string
- "lowpass"
- "highpass"
- "bandpass"
- "notch"
- "allpass"
- "peaking"
- "lowshelf"
- "highshelf"
- "resonant"
- 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
- returns coeffs [ b0, b1, b2, a1, a2 ] (a0 = 1)

Usage

DSP

`js
const coeffs = require("biquad-coeffs-maxmsp");

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

`js
const coeffs = require("biquad-coeffs-maxmsp");

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