Refer to the Audio Concepts section for more information on sample rates and bit depths. Below is a list of audio and music file formats, sorted by file extension. It includes a brief description of the file format and the name of a program that first used the files or is commonly used to create, edit or play them.
Audio Interchange File Format (or AIFF) is a file format for storing digital audio (waveform) data. It supports a variety of bit resolutions, sample rates, and channels of audio. This format is very popular upon Apple platforms, and is widely used in professional programs that process digital audio waveforms.
The Advanced Systems Format (ASF) is the preferred Windows Media file format. With Windows Media Player, if the appropriate codecs are installed on your computer, you can play audio content, video content, or both, that is compressed with a wide variety of codecs and that is stored in an .asf file. Additionally, you can stream audio and video content with Windows Media Services, or you can package that content with Windows Media Rights Manager.
ASF is an extensible file format that stores synchronized multimedia data. It supports data delivery over a wide variety of networks and protocols. It is also suitable for local playback. ASF supports advanced multimedia capabilities including extensible media types, component download, scalable media types, author-specified stream prioritization, multiple language support, and extensive bibliographic capabilities that include document and content management.
Typically, ASF files that contain audio content that is compressed with the Windows Media Audio (WMA) codec use the .wma extension. Similarly, ASF files that contain audio content, video content, or both, that is compressed with Windows Media Audio (WMA) and Windows Media Video (WMV) codecs use the .wmv extension. Finally, content that is compressed with any other codec use the generic .asf extension.
Windows Media Audio (.wma) files are Advanced Systems Format (.asf) files that include audio that is compressed with the Windows Media Audio (WMA) codec. By using a separate extension, users can install multiple players on their computer and associate certain players with the .wma extension for playback of audio-only sources.
Unix Audio (.au) files are UNIX-generated sound files.
CD Audio (.cda) tracks are audio files that are stored on CD media. You can play .cda files only from a CD-ROM. To test a .cda file, either try to play a different .cda file from your CD-ROM or try to play a .cda file from a different CD-ROM. The .cda files are representations of CD audio tracks and do not contain the actual pulse code modulation (PCM) information. You cannot play the file if you copy a .cda file from the CD-ROM to your hard disk.
The current standard for CD audio requires a sampling rate of 44.1 kHz and a sample size of 16 bits (2 bytes per sample). As a result, you need to store 2 x 44,100= 88,200 bytes of data every second to record in mono. Recording in stereo would require twice that much storage. That extrapolates to about 10 MB of data for every minute of stereo sound! It is for this reason that compression schemes such as MP3 are so important.
Musical Instrument Digital Interface (MIDI) is a standard protocol for the interchange of musical information between musical instruments, synthesizers, and computers. This standard defines the codes for a musical event that include the start of a note, its pitch, length, volume, and musical attributes, such as vibrato. It also defines codes for various button, dial, and pedal adjustments that are used on synthesizers.
This standard has also evolved from early MPEG work. It is an audio compression technology that is part of the MPEG-1 and MPEG-2 specifications. The Fraunhofer Institute developed MP3 in Germany in 1991. MP3 uses perceptual audio coding to compress CD-quality sound with almost the same fidelity.
Compressed audio format designed by Real Networks for playback in the Real Player application. Supports streaming over networks.
The Windows operating system uses the Wave Form Audio (WAV) file format to store sounds as waveforms. One minute of Pulse Code Modulation (PCM)-encoded sound can occupy as little as 644 kilobytes (KB) or as much as 27 megabytes (MB) of storage. This size of the storage space depends on the sampling frequency, the type of sound (mono or stereo), and the number of bits that are used for the sample.
Similar to the AVI and ASF format, WAV is only a file container. Audio content that is compressed with a wide variety of codecs and that is stored in a .wav file can be played back in Windows Media Player if the appropriate codecs are installed on the computer. The most common audio codecs that are used in .wav files include Microsoft Adaptive Differential Pulse Code Modulation (MS ADPCM) and uncompressed Pulse Code Modulation (PCM).