There are possibly even more audio formats than graphics formats, arising largely from the lack of standardisation in audio hardware. Though soundcards in PCs are not a particularly new innovation, there are still a great number of compatiblity issues. It's also quite difficult to compress large amounts of audio at sufficiently high quality that will download in a reasonable time (one minute of CD-quality audio uncompressed is around nine megabytes).

The most common raw audio formats are .wav files (Microsoft's proprietary audio format) and .au (originally developed by Sun Microsystems, popular on UNIX systems). Neither of these are compressed, and thus should only be used for short or low-quality samples.

You may also come across the .mid MIDI format; this consists of a stream of MIDI (Musical Instrument Digital Interface) data which plays on the soundcard's built-in synthesiser. It's much more compact than other formats, but needs a top-quality soundcard to sound good. It obviously can't store some types of data, such as voice or noise samples, but can be downloaded to electronic MIDI instruments such as keyboards.