MIDI Control is a useful little utility to make small modifications to existing MIDI files. You can change the play speed, transpose the piece (i.e. change its pitch), mute selected channels and change the instrument sound for each channel. The modified file can be played directly from MIDI control if you have the free GSPlayer MIDI Player installed (download from www.pdamusician.com). Otherwise you have still the option of saving the file and loading it with any other MIDI player.