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