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Digital Audio Formats

Hundreds of file formats exist for recording and playing digital sound and music files. While many of these file formats are software dependant — for example a Creative Labs Music File is a .cmf — there are several well-known and widely supported file formats. While different operating systems have different popular music file formats, we'll mainly focus on those that are most commonly used on Windows-based PCs.

Many different digital audio formats and different software are used to create, store and manipulate these files, the good news for consumers is that there is also a wide range of devices and products available that support multiple formats. Should you not have the correct device for playing a particular file, you can also look for software conversion tools that will convert one file type to another. Because some audio files are open standards and some are proprietary, chances are we'll be seeing a wide variety of digital audio formats for some time to come.

File Format and Codec
An audio file format and audio codec (compressor/decompressor) are two very different things. Audio codecs are the libraries that are executed in multimedia players. The audio codec is actually a computer program that compresses or decompresses digital audio data according to the audio file format specifications. For example, the WAV audio file format is usually coded in the OCM format, as are the popular Macintosh AIFF audio files.

Audio Formats
Audio Formats can be broken down into three main categories. Uncompressed formats, lossless compression formats, and lossy compression.

Key Terms To Understanding Digital Audio Formats

digital audio
Refers to the reproduction and transmission of sound stored in a digital format. This includes CDs as well as any sound files stored on a computer.

data compression
Storing data in a format that requires less space than usual.

lossless compression
Refers to data compression techniques in which no data is lost.

lossy compression
Refers to data compression techniques in which some amount of data is lost. Lossy compression technologies attempt to eliminate redundant or unnecessary information.

Webopedia's Audio Category

Uncompressed audio formats (often referred to as PCM formats) are just as the name suggests — formats that use no compression. This means all the data is available, at the risk of large file sizes. A WAV audio file is an example of an uncompressed audio file.

Lossless compression applies compression to an uncompressed audio file, but it doesn;t lose information or degrade the quality of the digital audio file. The WMA audio file format uses lossless compression.

Lossy compression will result in some loss of data as the compression algorithm eliminates redundant or unnecessary information — basically it tosses what it sees as irrelevant information. Lossy compression has become popular online because of its small file size, it is easier to transmit over the Internet. MP3 and Real Audio files uses a lossy compression.

Common Windows-compatible Audio Formats

MP3 (.mp3)
MP3 is the name of the file extension and also the name of the type of file for MPEG, audio layer 3. Layer 3 is one of three coding schemes (layer 1, layer 2 and layer 3) for the compression of audio signals. Layer 3 uses perceptual audio coding and psychoacoustic compression to remove all superfluous information (more specifically, the redundant and irrelevant parts of a sound signal. The stuff the human ear doesn't hear anyway). It also adds a MDCT (Modified Discrete Cosine Transform) that implements a filter bank, increasing the frequency resolution 18 times higher than that of layer 2. The result in real terms is layer 3 shrinks the original sound data from a CD (with a bit rate of 1411.2 kilobits per one second of stereo music) by a factor of 12 (down to 112-128kbps) without sacrificing sound quality.

WMA - Windows Media Audio (.wma)
Short for Windows Media Audio, WMA is a Microsoft file format for encoding digital audio files similar to MP3 though can compress files at a higher rate than MP3. WMA files, which use the ".wma" file extension, can be of any size compressed to match many different connection speeds, or bandwidths.

WAV (.wav)
WAV is the format used for storing sound in files developed jointly by Microsoft and IBM. Support for WAV files was built into Windows 95 making it the de facto standard for sound on PCs. WAV sound files end with a .wav extension and can be played by nearly all Windows applications that support sound.

Real Audio (.ra  .ram .rm)
Real Audio is a proprietary format, and is used for streaming audio that enables you to play digital audio files in real-time. To use this type of file you must have RealPlayer (for Windows or Mac), which you can download for free. Real Audio was developed by RealNetworks.

MIDI - Musical Instrument Digital Interface (.mid)
Short for musical instrument digital interface, MIDI is a standard adopted by the electronic music industry for controlling devices, such as synthesizers and sound cards, that emit music. At minimum, a MIDI representation of a sound includes values for the note's pitch, length, and volume. It can also include additional characteristics, such as attack and delay time.

Ogg (.ogg)
Ogg is an audio compression format, comparable to other formats used to store and play digital music, but differs in that it is free, open and unpatented. It uses Vorbis, a specific audio compression scheme that's designed to be contained in Ogg.

Converting Audio Formats
With a slew of software applications available today, consumers can convert one digital audio file format to virtually any other. many of the programs available today offer standard burning or converting tools to enable consumers to create CDs on their computer which can be played in home or car stereos. Usually these tools will convert or burn uncompressed WAV PCM, compressed WAV , MP3, and Ogg Vorbis.
 

Did You Know...
Marketing firm iSuppli predicts that total MP3 player shipments will expand to 132 million units in 2009, rising at a compound annual growth rate (CAGR) of 29.1% from 36.8 million in 2004.  [iSuppli]


Vangie 'Aurora' Beal
Writer, www.Webopedia.com
Last updated: September 30, 2005


Related Links

"Did You Know...?" When Is Downloading Music on the Internet Illegal
For many people it is as simple as opening one of many peer-to-peer file share programs, selecting the tracks, downloading and burning to a CD-ROM. What isn't so simple about downloading music is the copyright protection laws that people break everyday by downloading some music tracks off the Internet.

MP3 AND AAC EXPLAINED (PDF)
The last years have shown widespread proliferation of .mp3-files, both from legal and illegal sources. Yet most people using these audio files do not know much about audio compression and how to use it. The paper gives an introduction to audio compression for music file exchange. Beyond the basics the focus is on quality issues and the compression ratio / audio bandwidth / artifacts tradeoffs.

Digital Audio Formats
Digital audio comes in many different formats, and multiple formats will be a fact of life for the foreseeable future. Groups like MPEG have created open standards, but even formats based on the same MPEG standard may not compatible with each other because of proprietary components.

JUMBO Audio & MP3 Downloads
Find free and trial versions of music & sound editors, encoders, plug-ins, and more!

Planet of Tunes
An overview of digital audio file formats and codecs.

Digital Audio Preservation Handbook (PDF)
Sound in its original state is a series of air vibrations (compressions and rarefactions), which are captured by our ears and then converted to electronic impulses for interpretation.

Real Player
Mix, burn, or play every major media format.