rochars / wavefile

 * Copyright (c) 2019 Rafael da Silva Rocha.

 *

 * 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 resample function.

 * @see https://github.com/rochars/wavefile

 */

import { Interpolator } from './interpolator';

import { FIRLPF } from './fir-lpf';

/**

 * Change the sample rate of the samples to a new sample rate.

 * @param {!Array|!TypedArray} samples The original samples.

 * @param {number} oldSampleRate The original sample rate.

 * @param {number} sampleRate The target sample rate.

 * @param {?Object} details The extra configuration, if needed.

 * @return {!Float64Array} the new samples.

 */

/**

 * Upsample.

 * @param {!Array|!TypedArray} samples The original samples.

 * @param {!Float64Array} newSamples The container for the new samples.

 * @param {Object} interpolator The interpolator.

 * @param {number} sampleRate The target sample rate.

 * @param {number} oldSampleRate The original sample rate.

 * @param {number} LPForder The LPF order.

 * @return {!Float64Array}

 * @private

 */

function upsample_(

  samples, newSamples, interpolator, sampleRate, oldSampleRate, LPForder) {

  // Resample and filter

  let filter = new FIRLPF(LPForder, sampleRate, (oldSampleRate / 2));

  for (let i=0; i< newSamples.length; i++) {

    newSamples[i] = filter.filter(interpolator.interpolate(i, samples));

  }

  // Reverse filter

  filter = new FIRLPF(LPForder, sampleRate, (oldSampleRate / 2));

  for (let i = newSamples.length - 1; i >= 0; i--) {

    newSamples[i]  = filter.filter(newSamples[i]);

  }

  return newSamples;

}

/**

 * Downsample.

 * @param {!Array|!TypedArray} samples The original samples.

 * @param {!Float64Array} newSamples The container for the new samples.

 * @param {Object} interpolator The interpolator.

 * @param {number} sampleRate The target sample rate.

 * @param {number} oldSampleRate The original sample rate.

 * @param {number} LPForder The LPF order.

 * @return {!Float64Array}

 * @private

 */

function downsample_(

  samples, newSamples, interpolator, sampleRate, oldSampleRate, LPForder) {

  // Filter

  let filter = new FIRLPF(LPForder, oldSampleRate, sampleRate / 2);

  for (let i = 0; i < samples.length; i++) {

    samples[i]  = filter.filter(samples[i]);

  }

  // Reverse filter

  filter = new FIRLPF(LPForder, oldSampleRate, sampleRate / 2);

  for (let i = samples.length - 1; i >= 0; i--) {

    samples[i]  = filter.filter(samples[i]);

  }

  // Resample

  for (let i=0; i< newSamples.length; i++) {

    newSamples[i] = interpolator.interpolate(i, samples);

  }

  return newSamples;

}