Search Physical Audio Signal Processing
Book Index | Global Index
Would you like to be notified by email when Julius Orion Smith III publishes a new entry into his blog?
Doppler Effect
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. You have probably heard the pitch of a horn
drop lower as it passes by (e.g., from a moving train). As a pitched
sound-source moves toward you, the pitch you hear is raised; as it
moves away from you, the pitch is lowered. The Doppler effect has
been used to enhance the realism of simulated moving sound sources for
compositional purposes [80], and it is an important
component of the ``Leslie effect'' (described in §5.9).
As derived in elementary physics texts, the Doppler shift is
given by
 |
(6.2) |
where

is the radian frequency emitted by the source at rest,

is the frequency received by the listener,

denotes the
speed of the listener relative to the
propagation medium in the
direction of the source,

denotes the speed of the source
relative to the propagation medium in the direction of the listener,
and

denotes
sound speed. Note that all quantities in this formula
are
scalars.
Subsections
Previous: Vibrato SimulationNext: Vector Formulation
About the Author: Julius Orion Smith III
Julius Smith's background is in electrical engineering (BS Rice 1975, PhD Stanford 1983). He is presently Professor of Music and Associate Professor (by courtesy) of Electrical Engineering at
Stanford's Center for Computer Research in Music and Acoustics (CCRMA), teaching courses and pursuing research related to signal processing applied to music and audio systems. See
http://ccrma.stanford.edu/~jos/ for details.