Because uncompressed audio files are so large--about 10 MB of storage for every minute of CD-quality audio--they are impractical for streaming and downloading over the internet.3.5 For network use, audio files are ``compressed'' to reduce their size, allowing for quicker downloads and real-time streaming.
Computers compress and decompress audio data by using software called a codec (COmpress/DECompress). Sometimes the term ``codec'' is used interchangeably with ``audio format,'' but there is an important difference: a codec is software that is used to interpret an audio format. In fact, in some cases several different codecs exist to compress and decompress a single audio format.
With compression, there is a tradeoff between file size and sound quality. Codecs that provide high levels of compression discard parts of the original audio to reduce the amount of data. The more data that is discarded, the smaller the audio file, but the loss of data also results in a degradation in sound quality.
Audio compression formats fall into three groups: formats defined by international standards (such as MPEG), proprietary formats (such as Windows Media and RealAudio), and open-source formats (such as Ogg Vorbis).
It is important to select the compression format that best meets your particular needs, and those needs often concern more than audio quality. The projected longevity of the format, its market share, its technical support, the requirements and limitations it imposes on hardware and software--all of these can be just as important as sound quality.