It is important to distinguish between a file format and a codec. A codec performs the encoding and decoding of the raw audio data while the data itself is stored in a file with a specific audio file format. Though most audio file formats support only one audio codec, a file format may support multiple codecs, as AVI does.

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There are three major groups of audio file formats:

• Uncompressed audio formats, such as WAV, AIFF and AU;
• formats with lossless compression, such as FLAC, Monkey's Audio (filename extension APE), WavPack (filename extension WV), Shorten, TTA, Apple Lossless and lossless Windows Media Audio (WMA); and
• formats with lossy compression, such as MP3, Vorbis, lossy Windows Media Audio (WMA) and AAC.

Uncompressed audio format

There is one major uncompressed audio format, PCM, which is usually stored as a .wav on Windows or as .aiff on Mac OS. WAV is a flexible file format designed to store more or less any combination of sampling rates or bitrates. This makes it an adequate file format for storing and archiving an original recording. A lossless compressed format would require more processing for the same time recorded, but would be more efficient in terms of space used. WAV, like any other uncompressed format, encodes all sounds, whether they are complex sounds or absolute silence, with the same number of bits per unit of time.

Let's take an example. A file contains a minute of a symphonic orchestra playing beautifully followed by a minute of silence. If the sound were stored in WAV, the same amount of data would be used for each half. If data were encoded with TTA, the first minute would be a bit smaller than in the WAV file, and the silent half would take almost no disc space at all. But then, recording in the TTA format would require a lot more processing than the WAV.

The WAV format is based on the RIFF file format, which is similar to the IFF format.

BWF (Broadcast Wave Format) is a standard audio format created by the European Broadcasting Union as a successor to WAV. BWF allows metadata to be stored in the file. See: European Broadcasting Union: Specification of the Broadcast Wave Format - A format for audio data files in broadcasting. EBU Technical document 3285, July 1997. This format is the primary recording format used in many professional Audio Workstations used in the Television and Film industry. Stand-alone file based multi-track recorders from Sound Devices, Zaxcom, HHB USA, Fostex, and Aaton all use BWF as their preferred file format for recording multi-track audio files with SMPTE Time Code reference. This standardized Time Stamp in the Broadcast Wave File allows for easy synchronization with a separate picture element.

Lossless audio formats

Lossless audio formats (such as TTA and FLAC) provide a compression ratio of about 2:1.

Free and Open File Formats

• wav - standard audio file format used mainly in Windows PCs. Commonly used for storing uncompressed (PCM), CD-quality sound files, which means that they can be large in size - around 10MB per minute of music. It is less well known that wave files can also be encoded with a variety of codecs to reduce the file size (for example the GSM or mp3 codecs). Wav files use a RIFF structure.
• ogg - a free, open source container format supporting a variety of codecs, the most popular of which is the audio codec Vorbis. Vorbis offers better compression than MP3 but is less popular.
• flac - a lossless compression codec. You can think of lossless compression as like zip but for audio. If you compress a PCM file to flac and then restore it again it will be a perfect copy of the original. (All the other codecs discussed here are lossy which means a small part of the quality is lost). The cost of this losslessness is that the compression ratio is not good. Flac is recommended for archiving PCM files where quality is important (eg. broadcast or music use).
• aiff - the standard audio file format used by Apple. It is like a wav file for the Mac.
• raw - a raw file can contain audio in any codec but is usually used with PCM audio data. It is rarely used except for technical tests.
• au - the standard audio file format used by Sun, Unix and Java. The audio in au files can be PCM or compressed with the ulaw, alaw or G729 codecs.