Audio file formats

WAV

A Wave file is an audio file format, created by Microsoft, which has become a standard PC audio file format for everything from system and game sounds to CD-quality audio. A Wave file is identified by a file name extension of WAV (.wav). Used primarily in PCs, the Wave file format has been accepted as a viable interchange medium for other computer platforms, such as Macintosh. This allows content developers to freely move audio files between platforms for processing, for example.

In addition to the uncompressed raw audio data, the Wave file format stores information about the file's number of tracks (mono or stereo), sample rate, and bit depth.

AIFF

AIFF (Audio Interchange File Format) is one of the two most-used audio file formats used in the Apple Macintosh operating system. The other is Sound Designer II (SDII). Most CD writers can accept AIFF or SDII files interchangeably when writing a Red Book audio CD. AIFF is sometimes referred to as "Apple Interchange File Format."

The extension for this file type is ".aif" when it is used on a PC. On a Mac, the file extension is not needed. A Mac file uses a Type and Creator resource to identify itself to the operating system and the applications that can open it.

An AIFF file contains the raw audio data, channel information (monophonic or stereophonic), bit depth, sample rate, and application-specific data areas. The application-specific data areas let different applications add information to the file header that remains there even if the file is opened and processed by another application. For example, a file could retain information about selected regions of the audio data used for recalling zoom levels not used by other applications.

MP3

  MP3 (MPEG-1 Audio Layer-3) is a standard technology and format for compression a sound sequence into a very small file (about one-twelfth the size of the original file) while preserving the original level of sound quality when it is played. MP3 files (identified with the file name suffix of ".mp3") are available for downloading from a number of Web sites. Many Windows 98 users will find that they have a player built into their operating system. Otherwise, you can download a player from one of several popular MP3 sites. MP3 files are usually download-and-play files rather than streaming sound files that you link-and-listen-to with RealPlayer and similar products (However, streaming MP3 is possible.) Winamp (PC), MacAmp (Mac), and mpeg123 (UNIX) are popular MP3 players, but there are many others. To create an MP3 file, you use a program called a ripper to get a selection from a CD onto your hard disk and another program called an encoder to convert the selection to an MP3 file. Most people, however, simply download MP3s from someone else and play them.

digital audio is typically created by taking 16 binary digit samples a second of the analog signal. Since this signal is typically spread out over a spectrum of 44.1 thousand cycles per second (kHz), this means that one second of CD quality sound requires 1.4 million bits of data. Using their knowledge of how people actually perceive sound, the developers of MP3 devised a compression algorithm that reduces data about sound that most listeners can not perceive. MP3 is currently the most powerful algorithm in a series of audio encoding standards developed under the sponsorship of the Motion Picture Experts Group (MPEG) and formalized by the International Organization for Standardization (ISO).