Musical Instrument Digital Interface (MIDI) is not really an audio standard: it specifies a method by which synthesizers and computers can communicate. Digitally coded information--such as "note-on," "volume," "pitch," and "patch change" (or instrument setting)--can be packaged in a MIDI file.
MIDI
A MIDI application can then "play" that information out of the computer to a sound card, an external MIDI synthesizer, or a software-based MIDI synthesizer. The data is then translated by the MIDI device and sent to the device's tone generating section. Finally the audio generated by the tone generating section is sent to its audio outputs and typically into a powered loudspeaker.

One result of this process is that the music you hear from an inexpensive MIDI device will sound much different from what you hear out of a more expensive one. And it's also important to note that in order for the specified instruments to play as expected through a standard General MIDI Device, they must conform to the General MIDI Specification, which is a subset of MIDI.

MIDI offers two big advantages over audio formats: first, file sizes are much smaller than their audio counterparts because they contain only controller information for MIDI synthesizers, and second, the sound quality will be as good as the audio quality of the synthesizer. In particular, MIDI output lacks the characteristic low level hiss and the limited high frequency response that exists with 8-bit audio.
Click the "play" button to hear a 30-secind MIDI example (10KB) using a MIDI plug-in such as Beatnik or MidPlug.
Otherwise, you may Download a this MIDI music example (10KB) and play it using a MIDI helper app.
(To download, PC users would "right mouse click" on the link; Mac users should click, hold, and select "save link...)