A Doppler effect is defined as a change in frequency of a wave caused by motion. You often hear it when police or ambulance sirens drop in pitch as they pass near by.
Use Doppler to dynamically alter or bend the pitch of the selection altering the speed at which the waveform is played. Note that both pitch and tempo are changed.
Shape Controls allow the pitch/speed to be varied over the selection from 0.25 to 2.0 times normal. Use Shape Volume to dynamically alter the volume as well.
The "Slow down" preset gives you a good idea of what it sounds like when the batteries start to fail in a portable tape player. Other presets can change your voice to a chipmunk ("Faster") or a giant ("Slower").
See Also: Pitch, Time, Shape Volume, Presets