tone
Version:
A Web Audio framework for making interactive music in the browser.
104 lines • 3.59 kB
JavaScript
import { ToneAudioNode, } from "../../core/context/ToneAudioNode.js";
import { optionsFromArguments } from "../../core/util/Defaults.js";
import { Gain } from "../../core/context/Gain.js";
/**
* A one pole filter with 6db-per-octave rolloff. Either "highpass" or "lowpass".
* Note that changing the type or frequency may result in a discontinuity which
* can sound like a click or pop.
* References:
* * http://www.earlevel.com/main/2012/12/15/a-one-pole-filter/
* * http://www.dspguide.com/ch19/2.htm
* * https://github.com/vitaliy-bobrov/js-rocks/blob/master/src/app/audio/effects/one-pole-filters.ts
* @category Component
*/
export class OnePoleFilter extends ToneAudioNode {
constructor() {
const options = optionsFromArguments(OnePoleFilter.getDefaults(), arguments, ["frequency", "type"]);
super(options);
this.name = "OnePoleFilter";
this._frequency = options.frequency;
this._type = options.type;
this.input = new Gain({ context: this.context });
this.output = new Gain({ context: this.context });
this._createFilter();
}
static getDefaults() {
return Object.assign(ToneAudioNode.getDefaults(), {
frequency: 880,
type: "lowpass",
});
}
/**
* Create a filter and dispose the old one
*/
_createFilter() {
const oldFilter = this._filter;
const freq = this.toFrequency(this._frequency);
const t = 1 / (2 * Math.PI * freq);
if (this._type === "lowpass") {
const a0 = 1 / (t * this.context.sampleRate);
const b1 = a0 - 1;
this._filter = this.context.createIIRFilter([a0, 0], [1, b1]);
}
else {
const b1 = 1 / (t * this.context.sampleRate) - 1;
this._filter = this.context.createIIRFilter([1, -1], [1, b1]);
}
this.input.chain(this._filter, this.output);
if (oldFilter) {
// dispose it on the next block
this.context.setTimeout(() => {
if (!this.disposed) {
this.input.disconnect(oldFilter);
oldFilter.disconnect();
}
}, this.blockTime);
}
}
/**
* The frequency value.
*/
get frequency() {
return this._frequency;
}
set frequency(fq) {
this._frequency = fq;
this._createFilter();
}
/**
* The OnePole Filter type, either "highpass" or "lowpass"
*/
get type() {
return this._type;
}
set type(t) {
this._type = t;
this._createFilter();
}
/**
* Get the frequency response curve. This curve represents how the filter
* responses to frequencies between 20hz-20khz.
* @param len The number of values to return
* @return The frequency response curve between 20-20kHz
*/
getFrequencyResponse(len = 128) {
const freqValues = new Float32Array(len);
for (let i = 0; i < len; i++) {
const norm = Math.pow(i / len, 2);
const freq = norm * (20000 - 20) + 20;
freqValues[i] = freq;
}
const magValues = new Float32Array(len);
const phaseValues = new Float32Array(len);
this._filter.getFrequencyResponse(freqValues, magValues, phaseValues);
return magValues;
}
dispose() {
super.dispose();
this.input.dispose();
this.output.dispose();
this._filter.disconnect();
return this;
}
}
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