low-pass-filter
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Low pass filter.
58 lines (54 loc) • 2.21 kB
JavaScript
/*
* Copyright (c) 2018-2019 Rafael da Silva Rocha.
* Copyright (c) 2011 James Robert, http://jiaaro.com
*
* 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 The low-pass-filter module.
* @see https://github.com/rochars/low-pass-filter
*/
/** @module low-pass-filter */
/**
* Low pass filter.
* @param {!Array<number>|TypedArray} samples The samples.
* @param {number} cutoff The cutoff frequency.
* @param {number} sampleRate The sample rate.
* @param {number} numChannels The number of channels.
*/
export function lowPassFilter(samples, cutoff, sampleRate, numChannels) {
let rc = 1.0 / (cutoff * 2 * Math.PI);
let dt = 1.0 / sampleRate;
let alpha = dt / (rc + dt);
let last_val = [];
let offset;
for (let i=0; i<numChannels; i++) {
last_val[i] = samples[i];
}
for (let i=0; i<samples.length; i++) {
for (let j=0; j< numChannels; j++) {
offset = (i * numChannels) + j;
last_val[j] =
last_val[j] + (alpha * (samples[offset] - last_val[j]));
samples[offset] = last_val[j];
}
}
}