Source Filter Theory
Pp. 231-252 (22)
Eric J. Hunter and Daniel Ludwigsen
Sources of sound exist all-around us. Sound sources are often accompanied
with a filter, and changes in the shape of the filter, like changes in the slide of a
trombone, has a strong impact on the emitted sound. We first describe two archetypes
of filters, the Helmholtz resonator and the pipe resonator. The Helmholtz resonator
consists of a larger cavity with a narrow opening, and the pipe resonator consists of a
We also describe an experimental approach that allows researchers to estimate the
resonance characteristic of both types of filters. Three types of sound sources are used
to test a resonator: a swept sine wave, a broadband noise, and an impulse. They can be
played as an input to “excite” the resonator, and the output can be recorded. The ratio
of the output over the input sound provides an image of the filter’s resonance
characteristics. A computational approach permits researchers to numerically predict
the resonance properties of the filter based on the geometrical dimensions of the filter.
The computational approach provides a reasonably accurate prediction of the resonance
characteristics of both types of filters. Finally, we apply these concepts to biological
systems focusing on human speech production.
/ attenuate, Filter, Formant, Mode of vibration, Resonance,
Department of Communicative Sciences and Disorders, Michigan State University, East Lansing, Michigan, USA.