The MIDI files are Musical Instrument Digital Interface files. Very small. Will play on most computers. Sound quality varies depending on how well your software synthesizes the notes.
The MP3 files are part of an evil plot using high technology to create low fidelity sound. These represent a poorly synthesized piano, are not compressed too much but are still around 8MB each (dial up warning). But it's good enough for practice.
|Soprano 2:||MIDI||mp3||(starts at bar 33)|
|Alto:||MIDI||mp3||(starts at bar 9)|