Introduction

The Doppler effect causes the pitch of a sound source to appear to rise or fall due to motion of the source and/or listener relative to each other. The Doppler effect has been used to enhance the realism of simulated moving sound sources for compositional purposes [4], and it is an important component of the ``Leslie effect.''

The Leslie is a popular audio processor used with electronic organs and other instruments [3,8]. It employs a rotating horn and rotating speaker port to ``choralize'' the sound. Since the horn rotates within a cabinet, the listener hears multiple reflections at different Doppler shifts, giving a kind of chorus effect. Additionally, the Leslie amplifier distorts at high volumes, producing a pleasing ``growl'' highly prized by keyboard players.

In this paper, an efficient algorithm for digital simulation of the Doppler effect is presented, and the algorithm is applied to the problem of rotating-horn simulation for the Leslie effect. In the next section, the Doppler effect is reviewed, followed by a description of the algorithm for its simulation. Next, the problem of rotating-horn simulation is discussed, followed by a description of a Leslie simulator.