Audio Glossary of Terms

AAC: Advanced Audio Coding, the lossy codec best known for its use in the Apple iPod and iTunes. May be labeled with filename extension M4A. Operates with or without FairPlay DRM.
AIFF: Audio Interchange File Format, an uncompressed file format codeveloped by Apple.
Bit rate: See data rate.
CDA: Compact Disc Audio. Shortcut that a computer operating system used to identify an uncompressed audio track on a CD. Not actually a file format. May refer to WAV or AIFF files.
Codec: An encode/decode format used to compress audio files. The encoding process reduces audio data to a more manageable file size. The decoding process occurs on playback.
Compression: Shrinking of audio file sizes using a codec, or encode/decode process. May be lossy, discarding some audible data, or lossless, precisely reconstructing the original signal with no loss in sound quality. Not to be confused with compression of analog audio signals or systems.
Data rate: The number of bits per second at which a codec operates. Affects quality of sound. Also known as sampling rate or bit rate.
DRM: Digital Rights Management. A controversial software feature that prevents unauthorized copying of copyrighted material. May also prevent DRM-protected files from playing on unauthorized devices. DRM is sometimes piggybacked onto AAC, WMA, and other proprietary codecs and file formats.
FLAC: Free Lossless Audio Codec. A codec that is lossless, therefore discarding no audible data; and open-source, therefore available for use by any software developer. Less efficient than a lossy format, more efficient than an uncompressed format.
Lossless: Refers to audio codecs that reduce data, cutting file size, but without discarding any data essential to sound quality. Examples: FLAC, Apple Lossless.
Lossy: Refers to audio codecs that reduce data, cutting file size, using psychoacoustic principles that identify data less essential to the ear. Examples include MP3, AAC, and WMA.
MP3: A lossy audio codec originally developed as the audio soundtrack for the MPEG-1 video codec. The most popular audio file format, used in many applications, including paid downloads, file sharing, and personal ripping of CDs for playback on a computer or music player.
MP3 Pro: An improved form of MP3 that offers better sound quality in smaller file sizes. Has yet to achieve the universality of original MP3.
MP3 VBR: MP3 Variable Bit Rate. An improved version of MP3 that adjusts compression from moment to moment, depending on the demands of the source material. Supported in newer hardware and software.
OGG: Open-source file format that supports open-source codecs that may be lossy or lossless.
Open-source: Refers to codecs and file formats that are not proprietary and not restricted by patents or licensing.
PCM: Pulse Code Modulation. Generic description of uncompressed digital audio. The CD is a 16-bit/44.1kHz PCM format. That means it samples a string of 16 zeroes and ones 44,100 times a second.
Proprietary codecs: Codecs bound by patent. For example, WMA is a proprietary codec owned by Microsoft. AAC was developed by AT&T, Dolby Labs, and other parties and licensed to Apple and other users.
Psychoacoustics: The study of human hearing and how it is influenced by the brain. In lossy audio codecs, psychoacoustic principles are applied to determine which audio data are less critical to the ear and therefore may be discarded to reduce file size.
Ripping: The encoding of an audio file, usually in a smaller file size than the original, using an audio codec.
Sampling rate: See data rate.
Uncompressed: Refers to an audio file that has not been subject to data reduction, either lossy or lossless. See compressed.
WAV: Windows Waveform. An audio file format that can be used to store uncompressed digital audio signals including, but not limited to, CD.
WMA: Windows Media Audio. Family of audio codecs owned by Microsoft. Includes lossy, lossless, and other formats.
WMA Lossless: Windows Media Audio Lossless. The lossless version of WMA, used to deliver high-quality downloads by MusicGiants.