Abstract
A novel approach to implement the distortion effect is introduced. The proposed approach is based on time-varying phase distortion of the input signal, and it is implemented using a coefficient-modulated first-order allpass filter. This new technique provides control over the distorted band with a proper choice of the modulating signal. By choosing a modulating signal that applies the phase distortion only for low frequencies, the aliasing often generated by conventional distortion effects, which modify the signal amplitude, can be greatly reduced. Modulation signals that produce distortion effects applicable for electric guitar playing are also discussed. Sound examples on the use of the filter can be found at http://www.acoustics.hut.fi/~jpekonen/Papers/dafx08/.
Keywords
Effects processing, distortion, allpass filters, time-varying filters
Files
- Paper (PDF, 294 KiB)
- Presentation slides (PDF, 289 KiB)
-
PureData (PD) implementation of the effect using
lowpass filtered input signal by Frank Barknecht, originally published via
PD mailing list,
on December 28, 2008. Contains the PD abstraction and a help file.
- zip-archive (1.5 KiB)
- tar.gz-archive (1.5 KiB)
-
The demo files listed below
- zip-archive (2.5 MiB)
- tar.gz-archive (2.5 MiB)
This page will be updated whenever new demos are prepared. If you find a nice modulation signal that produces a nice distortion effect, please send information about your choice associated with appropriate sound examples to the author of this page via email.
Demos
The demos below were presented at the conference, and they correspond to the examples on the presentation slides, on slide 9.
The sampling frequency used was 44.1 kHz. The guitar playing samples have not been fed through a loudspeaker emulator.
Example 1 - Intro from the theme of a Finnish children TV show called Rölli
- Input signal
- Modulated with a lowpass filtered input signal
- Modulated with an 800 Hz sine having values from -1 to 0.6