Book Image

Instant Audio Processing with Web Audio

By : Chris Khoo, Chris Keat Khoo
Book Image

Instant Audio Processing with Web Audio

By: Chris Khoo, Chris Keat Khoo

Overview of this book

Web Audio is an upcoming industry standard for web audio processing. Using the API, developers today can develop web games and applications with real-time audio effects to rival their desktop counterparts. Instant Audio Processing with Web Audio is your hands-on guide to the Web Audio API. Using clear, step-by-step exercises, this book explores the API and how to apply it to produce real-time audio effects such as audio stitching, audio ducking, and audio equalization. This book is an in-depth study of the Web Audio API. Through a series of practical, step-by-step exercises, this book will guide you through the basics of playing audio all the way to the task of building a 5-band audio equalizer. Along the way, we'll learn how to utilize Web Audio's scripting functionality to build real-time audio effects such as audio stitching and ducking. Then, we'll use this knowledge to build a basic audio layer step-by-step which can be used in our web applications/games. With its in-depth coverage of the Web Audio API and its practical advice on various audio implementation scenarios, Instant Audio Processing with Web Audio How-to is your ultimate guide to Web Audio.
Table of Contents (7 chapters)


Web Audio is a new audio API proposed by World Wide Web Consortium (W3C) to address the shortcomings of the existing HTML5 Audio API. This new API allows developers to perform advanced real-time audio processing/mixing that is just not possible with current standards.

In this book, we'll explore Web Audio's audio processing functionality through a series of recipes. We'll also apply our learning towards building an audio system. By the end of the book, we will have a clear grasp of the Web Audio API, its design philosophy, and how to utilize it to put together a plethora of audio effects.

Web Audio is a fairly new API. As a result, many browsers do not yet support it. The list of web browsers which currently support it is a short one; they are Chrome for PC and Mac (v10 or higher), and Safari for PC and Mac (v6 or higher).Firefox has slated to support Web Audio in its next release (Version 19).

The Web Audio API is a big subject matter for an Instant book. In fact, it's so large that we'll jump straight into Web Audio's audio manipulation functionality. But don't worry, we're providing bonus online recipes which focus on the basic aspects of the API which we skipped over.

What this book covers

Setting Up a Web Host (Simple), will help us set up a local web host for our development environment.

Playing Audio in a Loop (Simple), will help us explore Web Audio's audio looping functionality as we build a simple sound player.

Setting the Volume (Simple), will guide us through an in-depth look at Web Audio's volume control functionality.

Automating Audio Parameters (Intermediate), will focus on Web Audio's timing and scheduling functionality, and use it to build a sound ducking audio processor.

Building an Equalizer Using BiquadFilterNode (Advanced), will cover Web Audio's built-in audio processing functionality while building a 5-band equalizer.

In addition, this book features the following bonus online recipes. These recipes are available at

Initializing Web Audio (Simple), will take a look at Web Audio initialization on various web browsers.

Playing Audio Files (Simple), will cover Web Audio's design and playback fundamentals as we implement a sound player.

Scheduling Audio Playback (Intermediate), will explore Web Audio's timing functionality as we build a sound player capable of stitching audio playback seamlessly.

What you need for this book

The following applications are required in order to follow all the recipes:

  • Chrome or Safari web browser (we need a Web Audio-capable web browser in order to run the recipes).

  • Apache Web Server (we have to host the recipes on a local web server in order to function properly. Most of the recipes rely on audio data loaded via AJAX and AJAX functions properly, only if the requested data is hosted on a web server. I've chosen to use Apache as the local web server of choice, as it is available for virtually all operating systems).

If you are installing it for the first time, I recommend installing XAMPP. XAMPP is a free and open source web server package which includes Apache Web Server as part of its bundle. The XAMPP installer and set up instructions are available at

You'll also need a text editor as we'll be writing CSS, HTML, and JavaScript code. While simple text editors such as Notepad or Vim will suffice, I recommend choosing a JavaScript editor with good autocomplete functionality, as we'll be spending a large part of our time writing JavaScript. A good and free JavaScript editor is Komo Edit (

Who this book is for

This book is meant for programmers who already have some HTML and JavaScript programming experience and who are seeking to learn how to use Web Audio in their applications. Experience with AJAX and web server installation/configuration will be good, but is not a necessity in order to follow the contents.


In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text are shown as follows: " The recipes of this book assume that the recipe application root is the webaudio subdirectory."

A block of code is set as follows:

Alias /mywebaudio /webaudio

<Directory "/webaudio">
    Order allow,deny
    Allow from all

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

    sourceNode.loop = true;
    // Specify a custom loop segment
    sourceNode.loopStart = audioBuffer.duration * 0.5;
    sourceNode.loopEnd = audioBuffer.duration;
    // Keep track of the active sound loop

New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: "clicking the Next button moves you to the next screen".


Warnings or important notes appear in a box like this.


Tips and tricks appear like this.

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