Initial commit of new ChromeVox earcon engine.

chrome/browser/resources/chromeos/chromevox/cvox2/background/earcon_engine.js

Index: chrome/browser/resources/chromeos/chromevox/cvox2/background/earcon_engine.js
diff --git a/chrome/browser/resources/chromeos/chromevox/cvox2/background/earcon_engine.js b/chrome/browser/resources/chromeos/chromevox/cvox2/background/earcon_engine.js
new file mode 100644
index 0000000000000000000000000000000000000000..185aa8c931acffb639631f79c5ba9891c8657cb5
--- /dev/null
+++ b/chrome/browser/resources/chromeos/chromevox/cvox2/background/earcon_engine.js
@@ -0,0 +1,687 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * @fileoverview This is the low-level class that generates ChromeVox's
+ * earcons. It's designed to be self-contained and not depend on the
+ * rest of the code.
+ */
+
+goog.provide('EarconEngine');
+
+/**
+ * EarconEngine generates ChromeVox's earcons using the web audio API.
+ * @constructor
+ */
+EarconEngine = function() {
+  // Public control parameters. All of these are meant to be adjustable.
+
+  /** @type {number} The master volume, as an amplification factor. */
+  this.masterVolume = 0.2;
+
+  /** @type {number} The base relative pitch adjustment, in half-steps. */
+  this.masterPitch = -4;
+
+  /** @type {number} The click volume, as an amplification factor. */
+  this.clickVolume = 0.4;
+
+  /** @type {number} The volume of the static sound, as an ampl factor. */

[Peter Lundblad, 2015/08/11 11:15:28]

nit: be consistent ampl vs. amplification

[dmazzoni, 2015/09/14 18:06:37]

Done.

+  this.staticVolume = 0.2;
+
+  /** @type {number} The base delay for repeated sounds, in ms. */
+  this.baseDelay = 45;

[Peter Lundblad, 2015/08/11 11:15:29]

Since many other times are in whole seconds, should be be consistent and make
all times in either seconds or milliseconds?

[dmazzoni, 2015/09/14 18:06:37]

Done.

+
+  /** @type {number} The master stereo panning, from -1 to 1. */
+  this.masterPan = 0;
+
+  /** @type {number} The master reverb level as an ampl factor. */
+  this.masterReverb = 0.4;
+
+  /** @type {string} The choice of the reverb impulse response to use. */

[Peter Lundblad, 2015/08/11 11:15:28]

Say that this must we one of the items of EarconEngine.REVERBS

[dmazzoni, 2015/09/14 18:06:37]

Done.

+  this.reverbSound = 'small_room_2';
+
+  /** @type {number} The base pitch for the 'wrap' sound in half-steps. */
+  this.wrapPitch = 0;
+
+  /** @type {number} The base pitch for the 'alert' sound in half-steps. */
+  this.alertPitch = 0;
+
+  /** @type {string} The choice of base sound for most controls. */
+  this.controlSound = 'control';
+
+  /** @type {number} The delay between sounds in the on/off sweep effect. */

[Peter Lundblad, 2015/08/11 11:15:29]

.. in ms ?

[dmazzoni, 2015/09/14 18:06:37]

Done.

+  this.sweepDelay = 0.045;
+
+  /** @type {number} The delay between echos in the on/off sweep. */

[Peter Lundblad, 2015/08/11 11:15:29]

In ms ?

[dmazzoni, 2015/09/14 18:06:37]

Done.

+  this.sweepEchoDelay = 0.15;
+
+  /** @type {number} The number of echos in the on/off sweep. */
+  this.sweepEchoCount = 3;
+
+  /** @type {number} The pitch offset of the on/off sweep, in half-steps. */
+  this.sweepPitch = -7;
+
+  /** @type {number} The final gain of the progress sound, as an ampl factor. */
+  this.progressFinalGain = 0.05;
+
+  /** @type {number} The multiplicative decay rate of the progress ticks. */
+  this.progressGain_Decay = 0.7;
+
+  // Private variables.
+
+  /** @type {AudioContext} @private */
+  this.context_ = new AudioContext();
+
+  /**
+    * @type {Object<string, AudioBuffer>} A map between the name of an
+    *     audio data file and its loaded AudioBuffer.
+    * @private
+    */
+  this.buffers_ = {};
+
+  /**
+   * The source audio nodes for queued tick / tocks for progress.
+   * Kept around so they can be canceled.
+   *
+   * @type {?Array<AudioNode>}
+   * @private
+   */
+  this.progressSources_ = null;

[Peter Lundblad, 2015/08/11 11:15:28]

Do you need the distinction between null and empty array here?

[dmazzoni, 2015/09/14 18:06:37]

Done.

+
+  /** @type {number} The current gain for progress sounds. @private */
+  this.progressGain_ = 1.0;
+
+  /** @type {?number} The current time for progress sounds. @private */
+  this.progressT_ = null;

[Peter Lundblad, 2015/08/11 11:15:28]

Is it very beneficial to use T instead of Time here?  Also, document when this
is null.

[dmazzoni, 2015/09/14 18:06:37]

Done.

+
+  /** @type {?number} The window.setInterval ID for progress sounds.

[Peter Lundblad, 2015/08/11 11:15:29]

nit: start and end comment tokens on their own lines.

[dmazzoni, 2015/09/14 18:06:37]

Done.

+    * @private */
+  this.progressIntervalID_ = null;
+
+  // Initialization: load the base sound data files asynchronously.
+  EarconEngine.SOUNDS.forEach((function(sound) {

[Peter Lundblad, 2015/08/11 11:15:28]

Could save some repetitive code by concatenating the lists.
(The reason I suggest this here where it might seem marginally useful
is pu8rely readability.)  Your call.

[dmazzoni, 2015/09/14 18:06:37]

Done.

+    var url = EarconEngine.BASE_URL + sound + '.wav';
+    this.loadSound(sound, url);
+  }).bind(this));
+  EarconEngine.REVERBS.forEach((function(reverb) {
+    var url = EarconEngine.BASE_URL + reverb + '.wav';
+    this.loadSound(reverb, url);
+  }).bind(this));
+};
+
+/**
+ * @type {Array<string>} The list of sound data files to load.

[Peter Lundblad, 2015/08/11 11:15:29]

@const

[dmazzoni, 2015/09/14 18:06:37]

Done.

+ */
+EarconEngine.SOUNDS = [
+  'control',
+  'selection',
+  'selection_reverse',
+  'skim',
+  'static'];
+
+/**
+ * @type {Array<string>} The list of reverb data files to load.

[Peter Lundblad, 2015/08/11 11:15:28]

@const

[dmazzoni, 2015/09/14 18:06:37]

Done.

+ */
+EarconEngine.REVERBS = [
+  'small_room_2'];
+
+/**
+ * @type {number} The scale factor for one half-step.

[Peter Lundblad, 2015/08/11 11:15:28]

@const

[dmazzoni, 2015/09/14 18:06:37]

Done.

+ */
+EarconEngine.HALF_STEP = Math.pow(2.0, 1.0 / 12.0);
+
+/**
+ * @type {string} The base url for earcon sound resources.

[Peter Lundblad, 2015/08/11 11:15:28]

@cosnt

[dmazzoni, 2015/09/14 18:06:37]

Done.

+ */
+EarconEngine.BASE_URL = chrome.extension.getURL('cvox2/background/earcons/');
+
+/**
+ * Fetches a sound asynchronously and loads its data into an AudioBuffer.
+ *
+ * @param {string} sound The name of the sound to load.

[Peter Lundblad, 2015/08/11 11:15:29]

nit: call name?

[dmazzoni, 2015/09/14 18:06:37]

Done.

+ * @param {string} url The url where the sound should be fetched from.
+ */
+EarconEngine.prototype.loadSound = function(sound, url) {
+  var request = new XMLHttpRequest();
+  request.open('GET', url, true);
+  request.responseType = 'arraybuffer';
+
+  // Decode asynchronously.
+  request.onload = (function() {
+    this.context_.decodeAudioData(
+        /** @type {ArrayBuffer} */ (request.response),
+        (function(buffer) {
+          this.buffers_[sound] = buffer;
+        }).bind(this));
+  }).bind(this);
+  request.send();
+};
+
+/**
+ * Return an AudioNode containing the final processing that all
+ * sounds go through: master volume / gain, panning, and reverb.
+ * The chain is hooked up to the destination automatically, so you
+ * just need to connect your source to the return value from this
+ * method.
+ *
+ * @param {{gain: (number | undefined),
+ *          pan: (number | undefined),
+ *          reverb: (number | undefined)}} properties
+ *     An object where you can override the default
+ *     gain, pan, and reverb, otherwise these are taken from
+ *     masterVolume, masterPan, and masterReverb.
+ * @return {AudioNode} The filters to be applied to all sounds, connected
+ *     to the destination node.
+ */
+EarconEngine.prototype.createCommonFilters = function(properties) {
+  var gain = this.masterVolume;
+  if (properties.gain) {
+    gain *= properties.gain;
+  }
+  var gainNode = this.context_.createGain();
+  gainNode.gain.value = gain;
+  var first = gainNode;
+  var last = gainNode;
+
+  var pan = this.masterPan;
+  if (properties.pan) {

[Peter Lundblad, 2015/08/11 11:15:29]

Compare to undefined here. Else, a caller can't set pan to 0 (in case masterPan
was changed).  I'd recommend that for all numeric optional parameters
because it is fairly subttle.

[dmazzoni, 2015/09/14 18:06:37]

Good catch.

+    pan = properties.pan;
+  }
+  if (pan != 0) {
+    var panNode = this.context_.createPanner();
+    panNode.setPosition(pan, 0, -1);
+    panNode.setOrientation(0, 0, 1);
+    last.connect(panNode);
+    last = panNode;
+  }
+
+  var reverb = this.masterReverb;
+  if (properties.reverb)
+  reverb = properties.reverb;

[Peter Lundblad, 2015/08/11 11:15:28]

Indentation and please be consistent with one-line substatements either having
braces or not.

[dmazzoni, 2015/09/14 18:06:37]

Done.

+  if (reverb) {
+    var filter = this.context_.createConvolver();
+    filter.buffer = this.buffers_[this.reverbSound];
+
+    // Dry
+    last.connect(this.context_.destination);
+
+    // Wet
+    var reverbGainNode = this.context_.createGain();
+    reverbGainNode.gain.value = reverb;
+    last.connect(reverbGainNode);
+    reverbGainNode.connect(filter);
+    filter.connect(this.context_.destination);
+  } else {
+    last.connect(this.context_.destination);
+  }
+
+  return first;
+};
+
+/**
+ * High-level interface to play a sound from a buffer source by name,
+ * with some simple adjustments like pitch change (in half-steps),
+ * a start time (relative to the current time, in seconds),
+ * gain, panning, and reverb.
+ *
+ * The only required parameter is the name of the sound. The time, pitch,
+ * gain, panning, and reverb are all optional and are passed in an
+ * object of optional properties.
+ *
+ * @param {string} sound The name of the sound to play. It must already
+ *     be loaded in a buffer.
+ * @param {{pitch: (number | undefined),
+ *          time: (number | undefined),
+ *          gain: (number | undefined),
+ *          pan: (number | undefined),
+ *          reverb: (number | undefined)}=} opt_properties
+ *     An object where you can override
+ *     the default pitch, gain, pan, and reverb.

[Peter Lundblad, 2015/08/11 11:15:29]

nit: odd line break above. (short line)

[dmazzoni, 2015/09/14 18:06:37]

Done.

+ * @return {AudioBufferSourceNode} The source node, so you can stop it
+ *     or set event handlers on it.
+ */
+EarconEngine.prototype.play = function(sound, opt_properties) {
+  var source = this.context_.createBufferSource();
+  source.buffer = this.buffers_[sound];
+
+  if (!opt_properties) {
+    // This typecast looks silly, but the Closure compiler doesn't support
+    // optional fields in record types very well so this is the shortest hack.
+    opt_properties = /** @type {undefined} */({});
+  }
+
+  var pitch = this.masterPitch;
+  if (opt_properties.pitch) {
+    pitch += opt_properties.pitch;
+  }
+  if (pitch != 0) {
+    source.playbackRate.value = Math.pow(EarconEngine.HALF_STEP, pitch);
+  }
+
+  var destination = this.createCommonFilters(opt_properties);
+  source.connect(destination);
+
+  if (opt_properties.time) {
+    source.start(this.context_.currentTime + opt_properties.time);
+  } else {
+    source.start(this.context_.currentTime);
+  }
+
+  return source;
+};
+
+/**
+ * Play the static sound.
+ */
+EarconEngine.prototype.onStatic = function() {
+  this.play('static', {gain: this.staticVolume});
+};
+
+/**
+ * Play the link sound.
+ */
+EarconEngine.prototype.onLink = function() {
+  this.play('static', {gain: this.clickVolume});
+  this.play(this.controlSound, {pitch: 12});
+};
+
+/**
+ * Play the button sound.
+ */
+EarconEngine.prototype.onButton = function() {
+  this.play('static', {gain: this.clickVolume});
+  this.play(this.controlSound);
+};
+
+/**
+ * Play the text field sound.
+ */
+EarconEngine.prototype.onTextField = function() {
+  this.play('static', {gain: this.clickVolume});
+  this.play('static', {time: this.baseDelay * 0.0015,
+                       gain: this.clickVolume * 0.5});
+  this.play(this.controlSound, {pitch: 4});
+  this.play(this.controlSound,
+            {pitch: 4,
+             time: this.baseDelay * 0.0015,
+             gain: 0.5});
+};
+
+/**
+ * Play the pop up button sound.
+ */
+EarconEngine.prototype.onPopUpButton = function() {
+  this.play('static', {gain: this.clickVolume});
+
+  this.play(this.controlSound);
+  this.play(this.controlSound,
+            {time: this.baseDelay * 0.003,
+             gain: 0.2,
+             pitch: 12});
+  this.play(this.controlSound,
+            {time: this.baseDelay * 0.0045,
+             gain: 0.2,
+             pitch: 12});
+};
+
+/**
+ * Play the check on sound.
+ */
+EarconEngine.prototype.onCheckOn = function() {
+  this.play('static', {gain: this.clickVolume});
+  this.play(this.controlSound, {pitch: -5});
+  this.play(this.controlSound, {pitch: 7, time: this.baseDelay * 0.002});
+};
+
+/**
+ * Play the check off sound.
+ */
+EarconEngine.prototype.onCheckOff = function() {
+  this.play('static', {gain: this.clickVolume});
+  this.play(this.controlSound, {pitch: 7});
+  this.play(this.controlSound, {pitch: -5, time: this.baseDelay * 0.002});
+};
+
+/**
+ * Play the select control sound.
+ */
+EarconEngine.prototype.onSelect = function() {
+  this.play('static', {gain: this.clickVolume});
+  this.play(this.controlSound);
+  this.play(this.controlSound, {time: this.baseDelay * 0.001});
+  this.play(this.controlSound, {time: this.baseDelay * 0.002});
+};
+
+/**
+ * Play the slider sound.
+ */
+EarconEngine.prototype.onSlider = function() {
+  this.play('static', {gain: this.clickVolume});
+  this.play(this.controlSound);
+  this.play(this.controlSound,
+            {time: this.baseDelay * 0.001,
+             gain: 0.5,
+             pitch: 2});
+  this.play(this.controlSound,
+            {time: this.baseDelay * 0.002,
+             gain: 0.25,
+             pitch: 4});
+  this.play(this.controlSound,
+            {time: this.baseDelay * 0.003,
+             gain: 0.125,
+             pitch: 6});
+  this.play(this.controlSound,
+            {time: this.baseDelay * 0.004,
+             gain: 0.0625,
+             pitch: 8});
+};
+
+/**
+ * Play the skim sound.
+ */
+EarconEngine.prototype.onSkim = function() {
+  this.play('skim');
+};
+
+/**
+ * Play the selection sound.
+ */
+EarconEngine.prototype.onSelection = function() {
+  this.play('selection');
+};
+
+/**
+ * Play the selection reverse sound.
+ */
+EarconEngine.prototype.onSelectionReverse = function() {
+  this.play('selection_reverse');
+};
+
+/**
+ * Generate a synthesized musical note based on a sum of sinusoidals shaped
+ * by an envelope, controlled by a number of properties.
+ *
+ * The sound has a frequency of |freq|, or if |endFreq| is specified, does
+ * an exponential ramp from |freq| to |endFreq|.
+ *
+ * If |overtones| is greater than 1, the sound will be mixed with additional
+ * sinusoidals at multiples of |freq|, each one scaled by |overtoneFactor|.
+ * This creates a rounder tone than a pure sine wave.
+ *
+ * The envelope is shaped by the duration |dur|, the attack time |attack|,
+ * and the decay time |decay|, in seconds.
+ *
+ * As with other functions, |pan| and |reverb| can be used to override
+ * masterPan and masterReverb.
+ *
+ * @param {{gain: number,
+ *          freq: number,
+ *          endFreq: (number | undefined),
+ *          time: (number | undefined),
+ *          overtones: (number | undefined),
+ *          overtoneFactor: (number | undefined),
+ *          dur: (number | undefined),
+ *          attack: (number | undefined),
+ *          decay: (number | undefined),
+ *          pan: (number | undefined),
+ *          reverb: (number | undefined)}} properties
+ *     An object containing the properties that can be used to
+ *     control the sound, as described above.
+ */
+EarconEngine.prototype.generateSinusoidal = function(properties) {
+  var envelopeNode = this.context_.createGain();
+  envelopeNode.connect(this.context_.destination);
+
+  if (!properties.time) {

[Peter Lundblad, 2015/08/11 11:15:28]

Can you avoid modifying the passed in properties?

[dmazzoni, 2015/09/14 18:06:37]

Done.

+    properties.time = 0;
+  }
+
+  // Generate an oscillator for the frequency corresponding to the specified
+  // frequency, and then additional overtones at multiples of that frequency
+  // scaled by the overtoneFactor. Cue the oscillator to start and stop
+  // based on the start time and specified duration.
+  //
+  // If an end frequency is specified, do an exponential ramp to that end
+  // frequency.
+  var gain = properties.gain;
+  for (var i = 0; i < properties.overtones; i++) {
+    var osc = this.context_.createOscillator();
+    osc.frequency.value = properties.freq * (i + 1);
+
+    if (properties.endFreq) {
+      osc.frequency.setValueAtTime(
+          properties.freq * (i + 1),
+          this.context_.currentTime + properties.time);
+      osc.frequency.exponentialRampToValueAtTime(
+          properties.endFreq * (i + 1),
+          this.context_.currentTime + properties.dur);
+    }
+
+    osc.start(this.context_.currentTime + properties.time);
+    osc.stop(this.context_.currentTime + properties.time + properties.dur);
+
+    var gainNode = this.context_.createGain();
+    gainNode.gain.value = gain;
+    osc.connect(gainNode);
+    gainNode.connect(envelopeNode);
+
+    gain *= properties.overtoneFactor;
+  }
+
+  // Shape the overall sound by an envelope based on the attack and
+  // decay times.
+  envelopeNode.gain.setValueAtTime(
+      0, this.context_.currentTime + properties.time);
+  envelopeNode.gain.linearRampToValueAtTime(
+      1, this.context_.currentTime + properties.time + properties.attack);
+  envelopeNode.gain.setValueAtTime(
+      1, this.context_.currentTime + properties.time +
+          properties.dur - properties.decay);
+  envelopeNode.gain.linearRampToValueAtTime(
+      0, this.context_.currentTime + properties.time + properties.dur);
+
+  // Route everything through the common filters like reverb at the end.
+  var destination = this.createCommonFilters({});
+  envelopeNode.connect(destination);
+};
+
+/**
+ * Play a sweep over a bunch of notes in a scale, with an echo,
+ * for the ChromeVox on or off sounds.
+ *
+ * @param {boolean} reverse Whether to play in the reverse direction.
+ */
+EarconEngine.prototype.onChromeVoxSweep = function(reverse) {
+  var pitches = [-7, -5, 0, 5, 7, 12, 17, 19, 24];
+
+  if (reverse) {
+    pitches.reverse();
+  }
+
+  var attack = 0.015;
+  var dur = pitches.length * this.sweepDelay;
+
+  var destination = this.createCommonFilters({reverb: 2.0});
+  for (var k = 0; k < this.sweepEchoCount; k++) {
+    var envelopeNode = this.context_.createGain();
+    var startTime = this.context_.currentTime + this.sweepEchoDelay * k;
+    var sweepGain = Math.pow(0.3, k);
+    var overtones = 2;
+    var overtoneGain = sweepGain;
+    for (var i = 0; i < overtones; i++) {
+      var osc = this.context_.createOscillator();
+      osc.start(startTime);
+      osc.stop(startTime + dur);
+
+      var gainNode = this.context_.createGain();
+      osc.connect(gainNode);
+      gainNode.connect(envelopeNode);
+
+      for (var j = 0; j < pitches.length; j++) {
+        var freqDecay;
+        if (reverse)
+        freqDecay = Math.pow(0.75, pitches.length - j);

[Peter Lundblad, 2015/08/11 11:15:29]

Indentation.

[dmazzoni, 2015/09/14 18:06:37]

Done.

+        else
+        freqDecay = Math.pow(0.75, j);
+        var gain = overtoneGain * freqDecay;
+        var freq = (i + 1) * 220 *
+            Math.pow(EarconEngine.HALF_STEP, pitches[j] + this.sweepPitch);
+        if (j == 0) {
+          osc.frequency.setValueAtTime(freq, startTime + j * this.sweepDelay);
+          gainNode.gain.setValueAtTime(gain, startTime + j * this.sweepDelay);

[Peter Lundblad, 2015/08/11 11:15:28]

Seems like the second arguments on these two lines could be simplfied
since j is 0.

[dmazzoni, 2015/09/14 18:06:37]

Done.

+        } else {
+          osc.frequency.exponentialRampToValueAtTime(
+              freq, startTime + j * this.sweepDelay);
+          gainNode.gain.linearRampToValueAtTime(
+              gain, startTime + j * this.sweepDelay);
+        }
+        osc.frequency.setValueAtTime(
+            freq, startTime + j * this.sweepDelay + this.sweepDelay - attack);
+      }
+
+      overtoneGain *= 0.1 + 0.2 * k;
+    }
+
+    envelopeNode.gain.setValueAtTime(0, startTime);
+    envelopeNode.gain.linearRampToValueAtTime(1, startTime + this.sweepDelay);
+    envelopeNode.gain.setValueAtTime(1, startTime + dur - attack * 2);
+    envelopeNode.gain.linearRampToValueAtTime(0, startTime + dur);
+    envelopeNode.connect(destination);
+  }
+};
+
+/**
+ * Play the "ChromeVox On" sound.
+ */
+EarconEngine.prototype.onChromeVoxOn = function() {
+  this.onChromeVoxSweep(false);
+};
+
+/**
+ * Play the "ChromeVox Off" sound.
+ */
+EarconEngine.prototype.onChromeVoxOff = function() {
+  this.onChromeVoxSweep(true);
+};
+
+/**
+ * Play an alert sound.
+ */
+EarconEngine.prototype.onAlert = function() {
+  var freq1 = 220 * Math.pow(EarconEngine.HALF_STEP, this.alertPitch - 2);
+  var freq2 = 220 * Math.pow(EarconEngine.HALF_STEP, this.alertPitch - 3);
+  this.generateSinusoidal({attack: 0.02,
+                           decay: 0.07,
+                           dur: 0.15,
+                           gain: 0.3,
+                           freq: freq1,
+                           overtones: 3,
+                           overtoneFactor: 0.1});
+  this.generateSinusoidal({attack: 0.02,
+                           decay: 0.07,
+                           dur: 0.15,
+                           gain: 0.3,
+                           freq: freq2,
+                           overtones: 3,
+                           overtoneFactor: 0.1});
+};
+
+/**
+ * Play a wrap sound.
+ */
+EarconEngine.prototype.onWrap = function() {
+  this.play('static', {gain: this.clickVolume * 0.3});
+  var freq1 = 220 * Math.pow(EarconEngine.HALF_STEP, this.wrapPitch - 8);
+  var freq2 = 220 * Math.pow(EarconEngine.HALF_STEP, this.wrapPitch + 8);
+  this.generateSinusoidal({attack: 0.01,
+                           decay: 0.1,
+                           dur: 0.15,
+                           gain: 0.3,
+                           freq: freq1,
+                           endFreq: freq2,
+                           overtones: 1,
+                           overtoneFactor: 0.1});
+};
+
+/**
+ * Queue up a few tick/tock sounds for a progress bar. This is called
+ * repeatedly by setInterval to keep the sounds going continuously.
+ * @private
+ */
+EarconEngine.prototype.generateProgressTickTocks_ = function() {
+  while (this.progressT_ < this.context_.currentTime + 3.0) {
+    var t = this.progressT_ - this.context_.currentTime;
+    this.progressSources_.push(
+        [this.progressT_,
+         this.play('static',
+                   {gain: 0.5 * this.progressGain_,
+                    time: t})]);
+    this.progressSources_.push(
+        [this.progressT_,
+         this.play(this.controlSound,
+                   {pitch: 20,
+                    time: t,
+                    gain: this.progressGain_})]);
+
+    if (this.progressGain_ > this.progressFinalGain) {
+      this.progressGain_ *= this.progressGain_Decay;
+    }
+    t += 0.5;
+
+    this.progressSources_.push(
+        [this.progressT_,
+         this.play('static',
+                   {gain: 0.5 * this.progressGain_,
+                    time: t})]);
+    this.progressSources_.push(
+        [this.progressT_,
+         this.play(this.controlSound,
+                   {pitch: 8,
+                    time: t,
+                    gain: this.progressGain_})]);
+
+    if (this.progressGain_ > this.progressFinalGain) {
+      this.progressGain_ *= this.progressGain_Decay;
+    }
+
+    this.progressT_ += 1.0;
+  }
+
+  var removeCount = 0;
+  while (removeCount < this.progressSources_.length &&
+      this.progressSources_[removeCount][0] < this.context_.currentTime - 0.2) {
+    removeCount++;
+  }
+  this.progressSources_.splice(0, removeCount);
+};
+
+/**
+ * Start playing tick / tock progress sounds continuously until
+ * explicitly canceled.
+ */
+EarconEngine.prototype.startProgress = function() {
+  this.progressSources_ = [];
+  this.progressGain_ = 0.5;
+  this.progressT_ = this.context_.currentTime;
+  this.generateProgressTickTocks_();
+  this.progressIntervalID_ = window.setInterval(
+      this.generateProgressTickTocks_.bind(this), 1000);
+};
+
+/**
+ * Stop playing any tick / tock progress sounds.
+ */
+EarconEngine.prototype.cancelProgress = function() {
+  if (!this.progressIntervalID_) {
+    return;
+  }
+
+  for (var i = 0; i < this.progressSources_.length; i++) {
+    this.progressSources_[i][1].stop();
+  }
+  this.progressSources_ = [];
+
+  window.clearInterval(this.progressIntervalID_);
+  this.progressIntervalID_ = null;
+};