Available formats of free music
Before computers got big enough and fast enough to handle real-time multi-track sound recording and playback, but small enough to put into synthesizers, MIDI (Musical Instrument Digital Interface) made it possible to encode music as a low data rate stream of commands (to select instruments, for example) and events such as note on, note off, pitch bend, and others. MIDI was originally most suited to keyboards and guitars, where a string is activated by striking or picking, and then the sound evolves without any further intervention until it is cut off by dampers or releasing the string. Later additions to MIDI made it usable for string and wind instruments, by sending a stream of loudness commands. However, the wide range of timbre of an acoustic instrument could not be duplicated. MIDI has considerable advantages for students. For example, the tempo of a piece can be changed without changing pitches or expression. Any track can be silenced to create a do-it-yourself equivalent of Music Minus One, where the student plays the missing track to a complete accompaniment.
Although MIDIs are no longer the center of electronic musicmaking, there are many MIDI files still available on the Net, and a variety of Free Software for recording, playing, and editing MIDI files, and converting them to other formats.
- MIDI DataBase Rock Pop Themes Rap Dance Punk Blues Country MIDI Search
- The Classical Archives MIDIs and some MP3s
and many more.
 Sound files
There are numerous formats for sound files, including .wav, .mp3, and Ogg Vorbis. The MP3 format is the most widely used for sound and music. Since it is encumbered by patents, many Free Software sound programs use the free Ogg Vorbis format instead. Among the well-known sources for MP3 files are iTunes and e-music. The Vorbis.com Web site has a page of links to sources of Free files in Ogg Vorbis format.
The Ogg container format supported by OLPC allows other kinds of media, see the Ogg page.