Alias-free virtual analog oscillators using a feedback delay loop

TitleAlias-free virtual analog oscillators using a feedback delay loop
Publication TypeConference Proceedings
Year of Conference2009
AuthorsNam, J., V. Välimäki, J. S. Abel, and J. O. Smith III
Conference Namethe 12th Int. Conference on Digital Audio Effects
Date Published09/2009
Conference LocationComo, Italy
Keywordsanti-aliasing, delay-line, fractional-delay filter, oscillators, virtual analog
The rich spectra of classic waveforms (sawtooth, square and triangular)
are obtained by discontinuities in the waveforms or their
derivatives. At the same time, the discontinuities lead to aliasing
when the waveforms are digitally generated. To remove or reduce
the aliasing, researchers have proposed various methods,
mostly based on limiting bandwidth or smoothing the waveforms.
This paper introduces a new approach to generate the virtual
analog oscillators with no aliasing. The approach relies on
generating an impulse train using a feedback delay loop, often
used for the physical modeling of musical instruments. Classic
waveforms are then derived from the impulse train with a leaky
integrator. Although the output generated by this method is not
exactly periodic, it perceptually sounds harmonic. While additional
processing is required for time-varying pitch shifting, resulting
in some high-frequency attenuation when the pitch changes,
the proposed method is computationally more efficient than
other algorithms and the high-frequency attenuation can be also
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