Speedshifter is a practice tool from ABRSM that allows you to vary the speed of audio from CD or MP3 without altering the pitch.
Simply load a track and turn the dial to slow it down or speed it up - the pitch remains the same. If you load an ABRSM minus one track Speedshifter will know the starting tempo of the track and position the dial automatically at the correct point on the tempo/BPM ring.
Speedshifter is designed to be used whenever a student might benefit from playing along with the accompaniment at a reduced tempo. It can be used in a lesson (if there is a computer/laptop available), or it can be used by the student in their own practice sessions.
Because Speedshifter varies the speed of the audio recording, any fluctuation of tempo is kept. This ensures that Speedshifter provides, in many cases, a more musical solution to slow practice than a metronome.