THE JUDICIOUS USE OF AUDIO CAN ENHANCE ANY WEB PAGE OR MULTIMEDIA PRESENTATION. This article provides some guidelines for selecting the type of audio file, and its characteristics, for use in your project.
Before discussing the process of creating audio files, you should be familiar with some of their attributes.

The quality (fidelity) of sound when you play a digital audio file is determined by two attributes: resolution and sampling rate. The resolution of a sound file can be set to 8-bit or 16-bit, and the sampling rate options are 11.025 kilohertz (kHz), 22.05 kHz or 44.1 kHz (there are other options, but these are the most common ones). In addition, you can select to produce mono (1 channel) or stereo (2 channel) files. There are many possible combinations of these characteristics, but the most commonly used are shown on the following table:

So why don't we always use the highest quality? Higher quality means larger files; a minute of 16-bit stereo sound at 44.1 kHz (uncompressed) requires about 10 megabytes of disk space. The following graph shows the size and download times of a 10 second sound clip at the various settings.

There are a variety of sound file formats (types). These are some common ones:

• WAV (Waveform Audio) - the most widely used format on Windows-based PCs. Excellent for capture and editing, and suitable for web delivery. Can be imported into most sound processing or authoring applications.

• AIFF (Audio Interchange File Format) - similar to WAV files but native to the Macintosh platform.
  
• MP3 (MPEG-1 Layer 3) Offers high compression rates while maintaining very good quality. However, cannot be edited directly and additional software is required for playback through a web browser.

The process of creating audio files can be divided into three phases:

     1)planning    2)capturing the sound    3)processing the sound file.

The goal is to produce a digital sound file suitable for delivery using the desired medium.

1) Planning

In the planning phase you will determine the precise sounds you wish to record, the type of file to produce and its attributes.

• The delivery medium for your final presentation will determine the attributes of your sound files. For video and CD-ROM delivery you can use larger files, unlike web delivery which limits bandwidth.
  
  
• Your choices of sound processing and authoring software determine the type of file you create, as most applications only allow you to import certain formats.
  
  
• The target platform, particularly for web delivery, also determine the file type. Avoid creating files that require additional software or plug-ins for playback.

2) Capturing

In this phase you are taking analog sounds and recording them onto your hard drive, via the sound card, thereby producing a digital file which is your master file.

• If you have ample disk storage space, capture at the highest possible quality.
  
  
• Ensure audio levels (volume) are set correctly. Excessively high levels produce distortion, and low levels result in a lot of electronic noise (hums and such).
  
  
• Save in a common file format like WAV or AIFF without compression.

3) Processing

Once you have your master, use sound processing software to:

• Edit a large file into smaller files - recommended for voice files as it simplifies the synchronization of narration to visuals.
  
  
• Normalize to avoid passages that are too loud or soft.
  
  
• Reduce noise and eliminate unwanted 'clicks and pops'.
  
  
• Reduce the number of channels, resolution and sampling rate.
  
  
• Save the file to a format you can use in authoring, possibly compressing the file.
  

The following web sites provide additional information:

WebRef Audio

Project Cool - Audio

The Void - Your PC Audio Resource 

Alfredo Elias-Calles , Graduate Student
Dept. of Educational Technology
San Diego State University