A Digital Model of the Buchla Lowpass-Gate

Authors
Julian Parker1, Stefano D'Angelo1
Status
Published in Proceedings of the 16th International Conference on Digital Audio Effects (DAFx-13), pp. 278–285, Maynooth, Ireland, September 2013
1
Aalto University, Espoo, Finland
BibTeX
@inproceedings{parker2013lpg,
  title={A Digital Model of the Buchla Lowpass-Gate},
  author={Parker, Julian and D'Angelo, Stefano},
  booktitle={Proc. 16\textsuperscript{th} Intl. Conf. Digital Audio Effects (DAFx-13)},
  pages={278--285},
  month={September},
  year={2013},
  address={Maynooth, Ireland}
}

Abstract

In recent years there has been an increasing amount of interest in the style of synthesis implemented by Don Buchla in his instrument designs from the early 1960s until the present. A key part of the Buchla synthesizer and its characteristic quality is the ’lowpass gate’ filter and the acoustic-like plucked sounds that it provides. In this work we examine the circuit of the low-pass gate, both its audio and control portions. We propose a number of digital models of these circuits, as well as a model of the photoresistive optoisolator or ’vactrol’ used within them. In the case of the audio path of the device, we pay particular attention to maintaining desirable behavior under time-variation of its parameters. The resulting digital model retains much of the interesting character of the analog system, and is computationally cheap enough to use within a standard computer-music setup.

Implementation

Sound samples