Virtual Analog Buchla 259 Wavefolder

Fabián Esqueda, Henri Pöntynen, Julian D. Parker and Vesa Välimäki

Companion page for a paper in the 20th Conference on Digital Audio Effects (DAFx-17)
Edinburgh, UK, 5 — 9 September, 2017

Original paper available here.


An antialiased digital model of the wavefolding circuit inside the Buchla 259 Complex Waveform Generator is presented. Wavefolding is a type of nonlinear waveshaping used to generate complex harmonically-rich sounds from simple periodic waveforms. Unlike other analog wavefolder designs, Buchla's design features five op-amp-based folding stages arranged in parallel alongside a direct signal path. The nonlinear behavior of the system is accurately modeled in the digital domain using memoryless mappings of the input–output voltage relationships inside the circuit. We pay special attention to suppressing the aliasing introduced by the nonlinear frequency-expanding behavior of the wavefolder. For this, we propose using the bandlimited ramp (BLAMP) method with eight times oversampling. Results obtained are validated against SPICE simulations and a highly oversampled digital model. The proposed virtual analog wavefolder retains the salient features of the original circuit and is applicable to digital sound synthesis.

Sound Example

110-Hz input with rising amplitude

40-Hz input with rising amplitude

Sequence with modulated amplitude


Click here to download a MAX/MSP demo of the proposed model implemented using Gen~. The demo is constantly being updated, please come back for the latest version. Current version: Version 2.0, updated December 2017.