wavefile
Version:
Create, read and write wav files according to the specs.
104 lines (97 loc) • 3.1 kB
JavaScript
/*
* Copyright (c) 2019 Rafael da Silva Rocha.
* Copyright (c) 2014 Florian Markert
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*
*/
/**
* @fileoverview FIR LPF. Based on the FIR LPF from Fili by Florian Markert.
* @see https://github.com/rochars/wavefile
* @see https://github.com/markert/fili.js
*/
/**
* A FIR low pass filter.
*/
export class FIRLPF {
/**
* @param {number} order The order of the filter.
* @param {number} sampleRate The sample rate.
* @param {number} cutOff The cut off frequency.
*/
constructor(order, sampleRate, cutOff) {
/** @type {number} */
let omega = 2 * Math.PI * cutOff / sampleRate;
/** @type {number} */
let dc = 0;
this.filters = [];
for (let i = 0; i <= order; i++) {
if (i - order / 2 === 0) {
this.filters[i] = omega;
} else {
this.filters[i] = Math.sin(omega * (i - order / 2)) / (i - order / 2);
// Hamming window
this.filters[i] *= (0.54 - 0.46 * Math.cos(2 * Math.PI * i / order));
}
dc = dc + this.filters[i];
}
// normalize
for (let i = 0; i <= order; i++) {
this.filters[i] /= dc;
}
this.z = this.initZ_();
}
/**
* @param {number} sample A sample of a sequence.
* @return {number}
*/
filter(sample) {
this.z.buf[this.z.pointer] = sample;
/** @type {number} */
let out = 0;
for (let i = 0, len = this.z.buf.length; i < len; i++) {
out += (
this.filters[i] * this.z.buf[(this.z.pointer + i) % this.z.buf.length]);
}
this.z.pointer = (this.z.pointer + 1) % (this.z.buf.length);
return out;
}
/**
* Reset the filter.
*/
reset() {
this.z = this.initZ_();
}
/**
* Return the default value for z.
* @private
*/
initZ_() {
/** @type {!Array} */
let r = [];
for (let i = 0; i < this.filters.length - 1; i++) {
r.push(0);
}
return {
buf: r,
pointer: 0
};
}
}