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 covers the basics of audio graphs, typical graph configurations, audio nodes inside those graphs, loading sound files, and playing sounds back.

  2. Chapter 2 delves into precise scheduling of sound in the future, multiple simultaneous sounds, changing parameters directly or over time, and crossfading.

  3. Chapter 3 covers gain, volume, and loudness, as well as preventing clipping via metering and dynamics compression.

  4. Chapter 4 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 builds on the earlier chapters to dive into more advanced topics, including biquad filters, simulating acoustic environments, and spatialized sounds.

  6. In Chapter 6, we will take a break from synthesizing and manipulating sound, and analyze and visualize sound instead.

  7. Chapter 7 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.

This icon signifies a tip, suggestion, or general note.

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 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 .

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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!