rochars / frequency-sweep

index.js

/*
 * Copyright (c) 2018-2019 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 Function to create multi-stage frequency sweeps.
 * @see https://github.com/rochars/frequency-sweep
 */

/**
 * Waveform functions.
 * @private
 */
const WAVES = {
  noise: function(t, delta, phase, start, end, phi0) {

The parameter delta is not used and could be removed.

The parameter phase is not used and could be removed.

The parameter end is not used and could be removed.

The parameter start is not used and could be removed.

The parameter t is not used and could be removed.

The parameter phi0 is not used and could be removed.

    return Math.random() * (1 - (-1)) + (-1);
  },
  sine: function(t, delta, phase, start, end, phi0) {
    phase = 2 * Math.PI * t * (start + (end - start) * delta / 2);
    return Math.sin(phase + phi0);
  },
  triangle: function(t, delta, phase, start, end, phi0) {
    phase = 2 * Math.PI * t * (start + (end - start) * delta / 2);
    return (2 / Math.PI) * Math.asin(Math.sin(phase + phi0));
  },
  sawtooth: function(t, delta, phase, start, end, phi0) {
    phase = 2 * Math.PI * t * (start + (end - start) * (delta / 2)) / 2;
    return (2 / Math.PI) * Math.atan(Math.tan(phase + phi0));
  },
  square: function(t, delta, phase, start, end, phi0) {
    phase = 2 * Math.PI * t * (start + (end - start) * delta / 2);
    return Math.sign(Math.sin(phase + phi0));
  }
};

/**
 * Return the samples of a frequency sweep. The sweep may be divided
 * in segments, each using a different waveform (or noise), and each with
 * a start and end frequency.
 * @param {!Array<Object<string, string|number>>} sequence The sequence.
 *   Each item in the array must have the properties:
 *     start: Integer value, the start frequency of the segment.
 *     end: Integer value, the end frequency of the segment.
 *     time: Float value, the duration of the segment. 1 = 1 second.
 *     wave: String, "sine", "square", "triangle", "sawtooth" or "noise".
 * @param {number} sampleRate The sample rate.
 * @return {!Array<number>}
 */
export function sweep(sequence, sampleRate) {
  let phi0 = 0;
  let phase = 0;
  let numSamples = 0;
  let duration = 0;
  let delta = 0;
  let samples = [];
  for (let i = 0; i < sequence.length; i++) {
    numSamples = Math.round(sampleRate * sequence[i].time);
    duration = numSamples / sampleRate;
    for (let x = 0; x < numSamples; x++) {
      delta = x / numSamples;
      samples.push(
        WAVES[sequence[i].wave](
          duration * delta,
          delta, phase,
          sequence[i].start,
          sequence[i].end,
          phi0));
    }
    phase = 2 * Math.PI * duration *
        (sequence[i].start + (sequence[i].end - sequence[i].start) / 2);
    phi0 = phi0 + phase;
  }
  return samples;
}