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Figure 1: Circuit-bent Speak & Spell with MIDI control, Kurt James Werner, 2007

Figure 1 Circuit-bent Speak & Spell with MIDI control, Kurt James Werner, 2007

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Computer models of circuit-bent instruments are desirable for several reasons. Circuit bending is often performed on devices that are antiquated and fragile. A computer model is used for ar- chival purposes, to preserve historical sounds and practices. Cre- ating a circuit-bent instrument requires specialized knowledge and a significant time investment. A software model of a circuit- bent instrument (in an audio plugin, for instance) fits convenient- ly into various electronic music workflows, is not susceptible to physical damage or decay, and scales easily. A model’s insuscep- tibility to electrical damage enables fearless experimentation.
Computer models of circuit-bent instruments are desirable for several reasons. Circuit bending is often performed on devices that are antiquated and fragile. A computer model is used for ar- chival purposes, to preserve historical sounds and practices. Cre- ating a circuit-bent instrument requires specialized knowledge and a significant time investment. A software model of a circuit- bent instrument (in an audio plugin, for instance) fits convenient- ly into various electronic music workflows, is not susceptible to physical damage or decay, and scales easily. A model’s insuscep- tibility to electrical damage enables fearless experimentation.
Figure 3: Circuit-bent Roland TR-606, Kurt James Wer- ner, 2009/2011 The technique of Bit Bending arose out of circuit-bent instru- ments created by one of the authors (Kurt James Werner) be- tween 2008 and 2011. Werner worked on four circuit-bent in- struments in particular (Casio SK-1 and SK-5, and Roland TR- 505 and TR-626, as shown in Figure 3) which all featured banana jack patchbays connected to digital circuitry inside (ROM chips), allowing access to any number of reconfigurable patchbay con- nections. Further work on the Yamaha PSS-170 and PSS-270 involved putting switches and a patchbay in series with critical circuit traces (leading to the main FM synthesis chip), allowing them to be cut and rerouted at will, creating new and varied mu- sical effects. At this time, the author had also been using home- made clock circuits to enable controllable, floating clock rates for all of these devices (enabling arbitrary transposition, in effect). Part of these clock circuits was a binary counter chip that allowed quick clock pitching by exact octave increments.
Figure 3: Circuit-bent Roland TR-606, Kurt James Wer- ner, 2009/2011 The technique of Bit Bending arose out of circuit-bent instru- ments created by one of the authors (Kurt James Werner) be- tween 2008 and 2011. Werner worked on four circuit-bent in- struments in particular (Casio SK-1 and SK-5, and Roland TR- 505 and TR-626, as shown in Figure 3) which all featured banana jack patchbays connected to digital circuitry inside (ROM chips), allowing access to any number of reconfigurable patchbay con- nections. Further work on the Yamaha PSS-170 and PSS-270 involved putting switches and a patchbay in series with critical circuit traces (leading to the main FM synthesis chip), allowing them to be cut and rerouted at will, creating new and varied mu- sical effects. At this time, the author had also been using home- made clock circuits to enable controllable, floating clock rates for all of these devices (enabling arbitrary transposition, in effect). Part of these clock circuits was a binary counter chip that allowed quick clock pitching by exact octave increments.
The exciting results from these initial experiments led to the es- tablishment of a new technique for circuit bending: “Bit Bend- ing.” Bit Bending encompasses the insertion of one or more digi- tal logic chips in series with an existing or added circuit trace, in the context of creating a circuit-bent instrument, as shown in Figure 5. So far, Bit Bending has typically been accomplished by housing digital logic chips (counters, NAND gates, etc.) in small ABS project enclosures, and using banana cables to communicate signals and draw power from the main board.
The exciting results from these initial experiments led to the es- tablishment of a new technique for circuit bending: “Bit Bend- ing.” Bit Bending encompasses the insertion of one or more digi- tal logic chips in series with an existing or added circuit trace, in the context of creating a circuit-bent instrument, as shown in Figure 5. So far, Bit Bending has typically been accomplished by housing digital logic chips (counters, NAND gates, etc.) in small ABS project enclosures, and using banana cables to communicate signals and draw power from the main board.
Figure 4: Spectrogram of circuit-bent instrument with “Counter bend” tapped at successively more significant bits over time Experiments with shorting jacks on the patchbay through binary counters (connecting one jack to the input pin of the counter, and connecting another jack to various output pins of the counter) yielded even more interesting results. Tapping different output pins of the counter often cause octave-like effects. For instance, moving toward a more significant bit off the counter often causes tonal components of the instrument’s sound to drop by an octave but also causes secondary timbral and temporal effects. It is in- structive to note that if an arbitrary binary signal is input to a counter, each successively more significant bit off of the counter will result in a roughly one-octave drop in the spectral energy, but also result in a signal that gets closer and closer to a square wave (as shown in Figure 4). These techniques were also extend- ed to the use of non-counter digital logic chips.
Figure 4: Spectrogram of circuit-bent instrument with “Counter bend” tapped at successively more significant bits over time Experiments with shorting jacks on the patchbay through binary counters (connecting one jack to the input pin of the counter, and connecting another jack to various output pins of the counter) yielded even more interesting results. Tapping different output pins of the counter often cause octave-like effects. For instance, moving toward a more significant bit off the counter often causes tonal components of the instrument’s sound to drop by an octave but also causes secondary timbral and temporal effects. It is in- structive to note that if an arbitrary binary signal is input to a counter, each successively more significant bit off of the counter will result in a roughly one-octave drop in the spectral energy, but also result in a signal that gets closer and closer to a square wave (as shown in Figure 4). These techniques were also extend- ed to the use of non-counter digital logic chips.
Figure 7: Class hierarchy for ChipInput and ChipOutput
Figure 7: Class hierarchy for ChipInput and ChipOutput
Figure 6: CircuitBoard object schema vances time on all of its associated chips by one sample, a con- cept from unit generator (UGen) based synthesis frameworks (such as the Synthesis Toolkit (STK) [18] and ChucK [19]). A schematic diagram is shown in Figure 6.
Figure 6: CircuitBoard object schema vances time on all of its associated chips by one sample, a con- cept from unit generator (UGen) based synthesis frameworks (such as the Synthesis Toolkit (STK) [18] and ChucK [19]). A schematic diagram is shown in Figure 6.
Figure 8: Class hierarchy for Chip objects
Figure 8: Class hierarchy for Chip objects
Our case study extends the basic NCO framework by cascading two NCOs together as shown in Figure 10, and by adding Mul- tiplier and ADSR chips (corresponding to the voltage-controlled oscillator (VCA) and envelope generator (EG) in the typical ex- pression of FM synthesis) on the output of the SPtAC chips. The Modulator ADSR chip corresponds to typical FM enveloped con- trol of the Modulation Index (8), and the Carrier ADSR chip cor- responds to typical enveloped control of the overall amplitude of the signal. Figure 9: Numerically controller oscillator block dia- gram
Our case study extends the basic NCO framework by cascading two NCOs together as shown in Figure 10, and by adding Mul- tiplier and ADSR chips (corresponding to the voltage-controlled oscillator (VCA) and envelope generator (EG) in the typical ex- pression of FM synthesis) on the output of the SPtAC chips. The Modulator ADSR chip corresponds to typical FM enveloped con- trol of the Modulation Index (8), and the Carrier ADSR chip cor- responds to typical enveloped control of the overall amplitude of the signal. Figure 9: Numerically controller oscillator block dia- gram
We have produced a computer model of FM synthesis imple- mented with two cascaded NCOs using our software library for RLT. This working model is now ready to be Bit-Bent. Even a simple circuit can be bent or reconfigured in any number of ways. Here we present only a few of the possible Bit Bending modifications to this model. Figure 10: Implementation of 2-operator FM synthesis with numerically controlled oscillators block diagram
We have produced a computer model of FM synthesis imple- mented with two cascaded NCOs using our software library for RLT. This working model is now ready to be Bit-Bent. Even a simple circuit can be bent or reconfigured in any number of ways. Here we present only a few of the possible Bit Bending modifications to this model. Figure 10: Implementation of 2-operator FM synthesis with numerically controlled oscillators block diagram
Less intuitive Bit Bending extensions to the model involve inser- tion of additional circuitry along the main signal path. As shown in Figure 11, we inserted a Counter chip at the interface between the carrier SPtAC output and the ADSR multiplier. Taking dif- ferent pins off of this counter allows for complex, non-linear oc- tave-like effects that are familiar from Bit Bending in hardware. Figure 11: “Counter bend” block diagram
Less intuitive Bit Bending extensions to the model involve inser- tion of additional circuitry along the main signal path. As shown in Figure 11, we inserted a Counter chip at the interface between the carrier SPtAC output and the ADSR multiplier. Taking dif- ferent pins off of this counter allows for complex, non-linear oc- tave-like effects that are familiar from Bit Bending in hardware. Figure 11: “Counter bend” block diagram
Delay bends are highly sensitive to the delay amount, and intro- duce signal-dependent digital noise, which can have a variety of effects depending on the bend’s location in the signal path. Figure 12: “Delay bend” block diagram
Delay bends are highly sensitive to the delay amount, and intro- duce signal-dependent digital noise, which can have a variety of effects depending on the bend’s location in the signal path. Figure 12: “Delay bend” block diagram
Related topics:
Modeling and SimulationGlitch studiesDigital AudioGlitch Art
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