Web Audio API: Advanced Sound for Games and Interactive Apps

79 Pages·2013·2.07 MB·English

by  Boris Smus

Web Audio API
Boris Smus
Beijing • Cambridge • Farnham • Köln • Sebastopol • Tokyo
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To my parents: thank you for the music
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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 studying digital audio processing, having
conversations with audio experts, and experimenting 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
configurations, audio nodes inside those graphs, loading sound files, and
playing sounds back.
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 important 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
manipulating 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
determined by context.
TIP
This icon signifies a tip, suggestion, or general note.
CAUTION
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
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permission. Incorporating a significant amount of example 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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Thanks!
I am not an expert in digital signals processing, mastering, or mixing by any
stretch. I am a software engineer and amateur musician with enough interest in
digital audio to spend some time exploring the Web Audio API and wrapping my
head around some of its important concepts. To write this book, I had to
continually bug others with far more digital-audio experience than me. I’d like to
thank them for answering my questions, providing technical reviews for this
book, and encouraging me along the way.
Specifically, this book could not have been written without the generous
mentorship of Chris Rogers, the primary author of the Web Audio specification
and also its main WebKit/Chrome implementer. I owe many thanks to Chris
Wilson, who gave an incredibly thorough technical review of this book’s
content, and to Mark Goldstein, who spent a few late nights doing editorial
passes. My thanks to Kevin Ennis for donating webaudioapi.com for hosting
samples related to the book. Last but not least, I would have never written this
book without the support and interest of a vibrant Web Audio API community on
the Web.
Without further ado, let’s dive in!
Chapter 1. Fundamentals
This chapter will describe how to get started with the Web Audio API, which
browsers are supported, how to detect if the API is available, what an audio
graph is, what audio nodes are, how to connect nodes together, some basic node
types, and finally, how to load sound files and playback sounds.
A Brief History of Audio on the Web
The first way of playing back sounds on the web was via the <bgsound> tag,
which let website authors automatically play background music when a visitor
opened their pages. This feature was only available in Internet Explorer, and was
never standardized or picked up by other browsers. Netscape implemented a
similar feature with the <embed> tag, providing basically equivalent
functionality.
Flash was the first cross-browser way of playing back audio on the Web, but it
had the significant drawback of requiring a plug-in to run. More recently,
browser vendors have rallied around the HTML5 <audio> element, which
provides native support for audio playback in all modern browsers.
Although audio on the Web no longer requires a plug-in, the <audio> tag has
significant limitations for implementing sophisticated games and interactive
applications. The following are just some of the limitations of the <audio>
element:
No precise timing controls
Very low limit for the number of sounds played at once
No way to reliably pre-buffer a sound
No ability to apply real-time effects