Table Of ContentWeb Audio API
Boris Smus
Web Audio API
by Boris Smus
Copyright © 2013 Boris Smus. All rights reserved.
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ISBN: 978-1-449-33268-6
[LSI]
To my parents: thank you for the music
Table of Contents
Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
1. Fundamentals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
A Brief History of Audio on the Web 1
Games and Interactivity 2
The Audio Context 3
Initializing an Audio Context 4
Types of Web Audio Nodes 5
Connecting the Audio Graph 5
Power of Modular Routing 6
Loading and Playing Sounds 10
Putting It All Together 11
2. Perfect Timing and Latency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Timing Model 13
Precise Playback and Resume 13
Scheduling Precise Rhythms 15
Changing Audio Parameters 15
Gradually Varying Audio Parameters 16
Custom Timing Curves 18
3. Volume and Loudness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Equal Power Crossfading 23
Using Meters to Detect and Prevent Clipping 25
Dynamics Compression 28
4. Pitch and the Frequency Domain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Pitch and playbackRate 31
Multiple Sounds with Variations 32
v
Oscillator-Based Direct Sound Synthesis 34
5. Analysis and Visualization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Frequency Analysis 37
Animating with requestAnimationFrame 39
Visualizing Sound 40
6. Advanced Topics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Adding Effects via Filters 44
Procedurally Generated Sound 45
Room Effects 47
Spatialized Sound 49
Audio Processing with JavaScript 51
7. Integrating with Other Technologies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Setting Up Background Music with the <audio> Tag 53
Live Audio Input 54
Page Visibility and Audio Playback 55
8. Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
A. Deprecation Notes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
B. Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
vi | Table of Contents
Preface
Thank you for picking up the first book on the topic of the Web Audio API. When I
first learned of the Web Audio API, I was a complete digital-audio novice embarking
on a journey to learn and understand the API, as well as the underlying fundamental
audio concepts. This book is what I wish existed when I started experimenting with the
API in 2011. It is intended to be a springboard for web developers like I was, with little
to no digital-audio expertise. It contains the things I learned from about a year of study‐
ing digital audio processing, having conversations with audio experts, and experiment‐
ing with the API.
The theoretical bits will be filled in through asides, which will explain the concepts. If
you are a digital-audio guru, feel free to skip these. The practical bits will be illustrated
with code snippets to give you a better sense of how the API works in real life. Many of
the examples also include links to working samples that can be found on this Web Audio
API site.
Structure of This Book
This book aims to give a high-level overview of a number of important features of the
Web Audio API, but is not an exhaustive survey of every available feature. It is not
intended as a comprehensive guide, but as an easy starting point. Most sections of the
book start off by describing an application, outlining the problem and solution, and
then showing relevant sample JavaScript Web Audio API code. Interspersed theory
sections explain some of the underlying audio concepts in more general terms. The
book is structured in the following way:
1. Chapter 1, Fundamentals covers the basics of audio graphs, typical graph configu‐
rations, audio nodes inside those graphs, loading sound files, and playing sounds
back.
vii
2. Chapter 2, Perfect Timing and Latency delves into precise scheduling of sound in
the future, multiple simultaneous sounds, changing parameters directly or over
time, and crossfading.
3. Chapter 3, Volume and Loudness covers gain, volume, and loudness, as well as
preventing clipping via metering and dynamics compression.
4. Chapter 4, Pitch and the Frequency Domain is all about sound frequency, an im‐
portant property of periodic sound. We’ll also talk about oscillators and examining
sound in the frequency domain.
5. Chapter 5, Analysis and Visualization builds on the earlier chapters to dive into
more advanced topics, including biquad filters, simulating acoustic environments,
and spatialized sounds.
6. In Chapter 6, Advanced Topics, we will take a break from synthesizing and manip‐
ulating sound, and analyze and visualize sound instead.
7. Chapter 7, Integrating with Other Technologies talks about interfacing Web Audio
API with other web APIs like WebRTC and the <audio> tag.
The source code of the book itself is released under the Creative Commons license and
is available on GitHub.
Conventions Used in This Book
The following typographical conventions are used in this book:
Italic
Indicates new terms, URLs, email addresses, filenames, and file extensions.
Constant width
Used for program listings, as well as within paragraphs to refer to program elements
such as variable or function names, databases, data types, environment variables,
statements, and keywords.
Constant width bold
Shows commands or other text that should be typed literally by the user.
Constant width italic
Shows text that should be replaced with user-supplied values or by values deter‐
mined by context.
This icon signifies a tip, suggestion, or general note.
viii | Preface
This icon indicates a warning or caution.
Using Code Examples
This book is here to help you get your job done. In general, if this book includes code
examples, you may use the code in your programs and documentation. You do not need
to contact us for permission unless you’re reproducing a significant portion of the code.
For example, writing a program that uses several chunks of code from this book does
not require permission. Selling or distributing a CD-ROM of examples from O’Reilly
books does require permission. Answering a question by citing this book and quoting
example code does not require permission. Incorporating a significant amount of ex‐
ample code from this book into your product’s documentation does require permission.
We appreciate, but do not require, attribution. An attribution usually includes the title,
author, publisher, and ISBN. For example: “Web Audio API by Boris Smus (O’Reilly).
Copyright 2013 Boris Smus, 978-1-449-33268-6.”
If you feel your use of code examples falls outside fair use or the permission given above,
feel free to contact us at [email protected].
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Preface | ix
