Kurt James Werner, Jonathan S. Abel, Julius O. Smith [kwerner, abel ...

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Kurt James Werner, Jonathan S. Abel, Julius O. Smith. [kwerner, abel, jos ]@ccrma.stanford.edu. Abstract. We designed models of three TR-808 voice circuits ...
Three Models of Circuit-Bent TR-808 Voices: the Bass Drum, Cymbal, and Cowbell Kurt James Werner, Jonathan S. Abel, Julius O. Smith [kwerner, abel, jos ]@ccrma.stanford.edu Abstract

TR-808

We designed models of three TR-808 voice circuits which are physically-informed and derived as closed-form expressions in terms of electrical component values where possible. An important part of the performance practice of analog drum machines involves modifying their voices circuits. These techniques would be impossible to recreate in a digital model through structured sampling or blackbox modeling. Our physically-informed models are designed to respect this practice by allowing changes to the circuit topology and electrical component values. Ad-hoc simplifications reduce the models’ computational load without affecting perceptual accuracy.

A now-ubiquitous analog drum machine made by Roland in the early 1980s, “the 808” was instrumental in the development of hip hop, techno, and acid house. Drum machine hackers modified the voice circuits to expand its sonic palette far beyond the timbre controls available in the factory configuration.

Papers This poster summarizes results from three recent conference papers: 1. K. J. Werner, J. S. Abel, J. O. Smith, “A Physically-Informed, Circuit-Bendable, Digital Model of the Roland TR-808 Bass Drum Circuit”, in Proceedings of the 17th International Conference on Digital Audio Effects (DAFx-14), Erlangen, Germany, September 2014 2. K. J. Werner, J. S. Abel, J. O. Smith, “The TR-808 Cymbal: a Physically-Informed, CircuitBendable, Digital Model”, in Proceedings of the 11th Sound and Music Computing / 40th International Computer Music Conference, Athens, Greece, September 2014 3. K. J. Werner, J. S. Abel, J. O. Smith, “More Cowbell: a Physically-Informed, Circuit-Bendable, Digital Model of the TR-808 Cowbell ”, in Proceedings of the 137th International Audio Engineering Society Convention, Los Angeles, CA, October 2014

TR-808 with modification controls visible along left and right edges2 .

Bass Drum Overview

=⇒ Bass Drum model block diagram. 1

Bass Drum circuit diagram .

Bass Drum Evaluation

Cymbal Evaluation

Cowbell Evaluation

amplitude (volts)

1 0.5 0 SPICE physical model

−0.5 −1 0

0.002

0.004

0.006 0.008 time (seconds)

0.01

0.012

Time domain signals.

frequency (hertz)

58 SPICE physical model

56 54

Cymbal SPICE simulation.

Cowbell SPICE simulation.

Cymbal model output.

Cowbell model output.

52 50 48 0

0.05

0.1

0.15 time (seconds)

0.2

0.25

0.3

amplitude

Instantaneous frequency estimate. 0.5 0 −0.5 −1

0.5

1

1.5

2 2.5 3 time (seconds)

3.5

4

4.5

No machine gun effect in model.

References 1. Roland Corporation, “TR-808 Service Notes”, first edition, June 1980 2. Robin Whittle (Real World Interfaces), “Modifications for the Roland TR-808”, http://www.firstpr.com.au/rwi/tr-808/, 26 June 2014