reverbgen.js

// Copyright 2014 Alan deLespinasse, jipodine
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

"use strict";

var reverbGen = {};

(function() {

  /** Generates a reverb impulse response.

      @param {!Object} params TODO: Document the properties.
      @param {!function(!AudioBuffer)} callback Function to call when
        the impulse response has been generated. The impulse response
        is passed to this function as its parameter. May be called
        immediately within the current execution context, or later. */
  reverbGen.generateReverb = function(params, callback) {
    var sampleRate = params.sampleRate || 0;
    var numChannels = params.numChannels || 2;
    var fadeInTime = params.fadeInTime || 0;
    var decayThreshold = params.decayThreshold || -60;
    var decayTime = params.decayTime || 5;

    var fadeInSampleFrames = Math.round(fadeInTime * sampleRate);
    var decaySampleFrames = Math.round(decayTime * sampleRate);
    var numSampleFrames = fadeInSampleFrames + decaySampleFrames;
    var decayBase = Math.pow(dBToPower(decayThreshold), 1 / (numSampleFrames - 1));

    var context = new OfflineAudioContext(numChannels, numSampleFrames, sampleRate);

    if(context === null) {
      callback(null);
      return;
    }
    
    var reverbIR = context.createBuffer(numChannels, numSampleFrames, sampleRate);

    var fadeInFactor = 1 / (fadeInSampleFrames - 1);
    for (var i = 0; i < numChannels; i++) {
      var chan = reverbIR.getChannelData(i);
      for (var j = 0; j < numSampleFrames; j++) {
        chan[j] = randomSample() * Math.pow(decayBase, j);
      }
      for (var j = 0; j < fadeInSampleFrames; j++) {
        chan[j] *= j * fadeInFactor;
      }
    }

    applyGradualLowpass(reverbIR, params.lpFreqStart || 0, params.lpFreqEnd || 0,
                        params.fadeInTime + params.decayTime, callback);
  };

  /** Creates a canvas element showing a graph of the given data.

      @param {!Float32Array} data An array of numbers, or a Float32Array.
      @param {number} width Width in pixels of the canvas.
      @param {number} height Height in pixels of the canvas.
      @param {number} min Minimum value of data for the graph (lower edge).
      @param {number} max Maximum value of data in the graph (upper edge).
      @return {!CanvasElement} The generated canvas element. */
  reverbGen.generateGraph = function(data, width, height, min, max) {
    var canvas = document.createElement('canvas');
    canvas.width = width;
    canvas.height = height;
    var gc = canvas.getContext('2d');
    gc.fillStyle = '#000';
    gc.fillRect(0, 0, canvas.width, canvas.height);
    gc.fillStyle = '#fff';
    var xscale = width / data.length;
    var yscale = height / (max - min);
    for (var i = 0; i < data.length; i++) {
      gc.fillRect(i * xscale, height - (data[i] - min) * yscale, 1, 1);
    }
    return canvas;
  }

  /** Saves an AudioBuffer as a 16-bit WAV file on the client's host
      file system. Normalizes it to peak at +-32767, and optionally
      truncates it if there's a lot of "silence" at the end.

      @param {!AudioBuffer} buffer The buffer to save.
      @param {string} name Name of file to create. */
  reverbGen.saveWavFile = function(buffer, name) {
    var bitsPerSample = 16;
    var bytesPerSample = 2;
    var sampleRate = buffer.sampleRate;
    var numChannels = buffer.numberOfChannels;
    var channels = getAllChannelData(buffer);
    var numSampleFrames = channels[0].length;
    var scale = 32767;
    // Find normalization constant.
    var max = 0;
    for (var i = 0; i < numChannels; i++) {
      for (var j = 0; j < numSampleFrames; j++) {
        max = Math.max(max, Math.abs(channels[i][j]));
      }
    }
    if (max) {
      scale = 32767 / max;
    }

    var sampleDataBytes = bytesPerSample * numChannels * numSampleFrames;
    var fileBytes = sampleDataBytes + 44;
    var arrayBuffer = new ArrayBuffer(fileBytes);
    var dataView = new DataView(arrayBuffer);
    dataView.setUint32(0, 1179011410, true); // "RIFF"
    dataView.setUint32(4, fileBytes - 8, true); // file length
    dataView.setUint32(8, 1163280727, true); // "WAVE"
    dataView.setUint32(12, 544501094, true); // "fmt "
    dataView.setUint32(16, 16, true)         // fmt chunk length
    dataView.setUint16(20, 1, true);         // PCM format
    dataView.setUint16(22, numChannels, true); // NumChannels
    dataView.setUint32(24, sampleRate, true);  // SampleRate
    var bytesPerSampleFrame = numChannels * bytesPerSample;
    dataView.setUint32(28, sampleRate * bytesPerSampleFrame, true); // ByteRate
    dataView.setUint16(32, bytesPerSampleFrame, true);              // BlockAlign
    dataView.setUint16(34, bitsPerSample, true);                           // BitsPerSample
    dataView.setUint32(36, 1635017060, true);                   // "data"
    dataView.setUint32(40, sampleDataBytes, true);
    for (var j = 0; j < numSampleFrames; j++) {
      for (var i = 0; i < numChannels; i++) {
        dataView.setInt16(44 + j * bytesPerSampleFrame + i * bytesPerSample,
                          Math.round(scale * channels[i][j]), true);
      }
    }
    var blob = new Blob([arrayBuffer], {'type': 'audio/wav'});
    var url = window.URL.createObjectURL(blob);
    var linkEl = document.createElement('a');
    linkEl.href = url;
    linkEl.download = name;
    linkEl.style.display = 'none';
    document.body.appendChild(linkEl);
    linkEl.click();
  };

  /** Applies a constantly changing lowpass filter to the given sound.

      @private
      @param {!AudioBuffer} input
      @param {number} lpFreqStart
      @param {number} lpFreqEnd
      @param {number} lpFreqEndAt
      @param {!function(!AudioBuffer)} callback May be called
      immediately within the current execution context, or later.*/
  var applyGradualLowpass = function(input, lpFreqStart, lpFreqEnd, lpFreqEndAt, callback) {
    if (lpFreqStart == 0) {
      callback(input);
      return;
    }
    var channelData = getAllChannelData(input);

    var context = new OfflineAudioContext(input.numberOfChannels, channelData[0].length, input.sampleRate);

    if(context === null) {
      callback(null);
      return;
    }

    var player = context.createBufferSource();
    player.buffer = input;
    var filter = context.createBiquadFilter();

    lpFreqStart = Math.min(lpFreqStart, input.sampleRate / 2);
    lpFreqEnd = Math.min(lpFreqEnd, input.sampleRate / 2);

    filter.type = "lowpass";
    filter.Q.value = 0.0001;
    filter.frequency.setValueAtTime(lpFreqStart, 0);
    filter.frequency.exponentialRampToValueAtTime(lpFreqEnd, lpFreqEndAt);

    player.connect(filter);
    filter.connect(context.destination);
    player.start();
    context.oncomplete = function(event) {
      callback(event.renderedBuffer);
    };
    context.startRendering();

    // window.filterNode = filter;
  };

  /** @private
      @param {!AudioBuffer} buffer
      @return {!Array.<!Float32Array>} An array containing the Float32Array of each channel's samples. */
  var getAllChannelData = function(buffer) {
    var channels = [];
    for (var i = 0; i < buffer.numberOfChannels; i++) {
      channels[i] = buffer.getChannelData(i);
    }
    return channels;
  };

  /** @private
      @return {number} A random number from -1 to 1. */
  var randomSample = function() {
    return Math.random() * 2 - 1;
  };

  /** @private
      @return {number} An exponential gain value (1e-6 for -60dB*/
  var dBToPower = function(dBValue) {
    return Math.pow(10, dBValue / 10);
  };

}());