Three-part Invention / Sinfonia #6 in E Major (JS Bach)
(click above to listen)

A three-part invention is a musical conversation between 
three voices (which could be instrumental voices).

Notice each of the three voices entering one after another 
with the 10-note theme: middle voice, upper voice, then lower voice.

(Piece realized by John Sankey)

MIDI sequence(s) from the Classical Archives, by permission