Catjar in the Rye

Posted in Documentation on September 30th, 2012 by admin

“Catjar in the Rye” (or “Betty”, as she is know to her friends) is an experimental sound instrument built for Swedish composer Andreas Catjar. It combines a chaotic Benjolin synthesizer, extreme fuzz distortion unit, a speaker/contact-mic feedback system and “circuit-bending”-style body contacts into one rugged flightcase. The Benjolin features several modifications, including patchable routing banana jacks, LED lights for the three stages of its analog shift register and an external audio input. I hope to post some sounds and video later on, when Andreas has time to make them.

My thanks go out to Rob Hordijk, who designed the Benjolin circuit, and to Pete Edwards/Casper Electronics for his help in working out the modifications. You can read a few of my thoughts on using analog shift registers for chaotic sound synthesis in this post.

This instrument really represents exactly what I would like to be doing more of these days: customized design and construction of personal sound instruments based on circuits freely available within the DIY electronics community. Please get in touch if you have a project in mind!

“Catjar in the Rye” was commissioned to appear in the Institutet/Markus Öhrn/Nya Rampen theater production “We love Africa and Africa loves us”. The premier takes place on October 5, 2012 at Ballhaus Ost Berlin.

Now Playing

aluk todolooccult rock[2012 ajna offensive]

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Cryptography Studies

Posted in Documentation on April 13th, 2012 by admin

cryptography (study I) from macumbista on Vimeo.

I took a quick break from some soundtracking work to build and document this little box over the weekend. I have been interested in examining the use of simple analog implementations of pseudo-random number generators, akin to those used in encryption algorithms, for the chaotic production of sound patterns. One of the simplest pseudo-random number generators is a three-stage shift register with a non-linear feedback loop, such as that found in Rob Hordijk’s “Benjolin” instrument design.

Rungler schematic courtesy of Rob Hordijk, redrawn by Casper Electronics

The most interesting part of the Benjolin is a circuit Hordijk calls a “rungler” (the rest of the Benjolin being two simple oscillators and a resonant filter). It is made up of a shift register in the middle (U4, a 4021B integrated circuit), an XOR (eXclusive OR) logic gate created by one transistor and an op-amp on the left, and finally a rudimentary Digital-to-Analog converter built around another op-amp on the right. Note the feedback from the last stage of the shift register to one input of the XOR, or what could be called the “poor man’s ring modulator”. The other XOR input comes from one of the two oscillators (P1).

Hordijk writes:

The purpose of the rungler is to create short stepped patterns of variable length and speed. […] It needs two frequency sources to work and basically creates a complex interference pattern that can be fed back into the frequency parameters of the driving oscillators to create an unlimited amount of havoc.

The rungler is basically a CMOS shift register clocked by one oscillator and receiving its data input from the other oscillator. The output bits of the shift register are used as […] a 3 bit code that is fed into a 3 bit DA converter. This DA eight level output voltage is fed back to the oscillator frequency control inputs. The output of the DA is the ‘rungler CV signal'[…]

When the rungler signal is fed back to the frequency parameters of the oscillators it will change the triangle waveforms and pulse widths of the oscillator outputs[…]

The rungler will try to find a balanced state. In this way it behaves according to principle from Chaos Theory. There seems to be an unlimited amount of possible balanced states and when a balanced state is just slightly disturbed it can be noted that it takes a little time to find the next balanced state, with noticeable bifurcations, etc.

Now, a shift register itself is a quite simple idea; one has several stages, and information (an analog voltage in some cases, or a binary state in others) gets passed from one stage to the next every time the shift register gets a clock signal. Passing the last stage of the shift register back to the first results in a loop, however any sort of transformation done to the last stage before it gets sent back to the first (an XOR “ring modulation” in the Benjolin’s case) means that each iteration of the loop changes. This satisfies the basic requirements of chaotic syntheses: that there is feedback, that there is nonlinearity and that there is sensitivity to initial conditions. (see Slater, Dan, “Chaotic Sound Synthesis”, Computer Music Journal 22.2 19 September 1998, pp 12-19.)

Not surprisingly, analog shift registers such as the one produced by Serge Tcherepnin were often referred to as “arabesque generators”, as in this image from Synapse Magazine September/October 1976. However, we could also refer to this structure as a Lindenmayer, or L-system. An L-system is essentially a grammatical system which rewrites itself for every new iteration according to a system of rules.

Here is Lindenmayer’s original L-system for modeling the growth of algae:

variables : A B
constants : none
start : A
rules : (A → AB), (B → A)

which produces:

n = 0 : A
n = 1 : AB
n = 2 : ABA
n = 3 : ABAAB
n = 4 : ABAABABA

(Source: Wikipedia)

In Non-Standard Sound Synthesis with L-Systems, Stelios Manousakis refers to non-propagative L-systems as being similar to cellular automata algorithms in that the data produced doesn’t branch out and expand endlessly, but rather is used as rules for determining the output of each cell. In our 3 stage shift register example, the non-linear feedback applied to the last stage before it returns to the first would be the new “grammatical rule” applied to the next iteration.

Now, another term we could use to describe a chaotically-produced series of binary numbers with a high sensitivity to the initial conditions (or “seed”) of the process which creates them is a Pseudo-Random Number Generator (also know as a Deterministic Random Bit Generator). And many implementations of a PRNG use what are called Linear Feedback Shift Registers to create those bits, which are the basic building blocks of many sorts of encryption processes.

Our 3-bit Benjolin is a far cry from the 128- and 256-bit encryption algorithms commonly used for digital security today (to say nothing of the “uncrackable” 1024-bit scheme used by the RSA algorithm), and probably bears a closer resemblance to the “shuffle” feature on my ITunes, which “randomly” seems to play back the same 220 songs out of the 22,000 in my MP3 collection. Or, as quantum mechanics pioneer John von Neumann joked, “Anyone who considers arithmetical methods of producing random digits is, of course, in a state of sin.” For the purpose of creating generative sound compositions in realtime, however, these pseudo-random bits appear to provide an interesting and “musical” balance between randomness and structure.

Other circuits or projects involving the potentially chaotic use of shift registers and/or pseudo-random number generators include the CGS 34 ASR (which is of course influenced by the original Serge ASR), the CGS 31 Digital Noise, the random voltage generator from the Buchla 208 “Music Easel” and the mighty Klee Sequencer.

As a footnote, I have to add that the man who first uttered the name “L-system” to me is the same man whose film is now sitting on my desktop, waiting to be scored. So with this musing on the cyclical nature of the universe, I bid you farewell for now.

Now Playing

drudkheternal turn of the wheel[2012 season of mist]
earthangels of darkness demons of light II[2012 southern lord]
keith fullerton whitmangenerators[2012 editions mego]
mirroringforeign body[2012 kranky]
oren ambarchiaudience of one[2012 touch]

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Ghost Locket Triptych

Posted in Documentation on October 12th, 2011 by admin

Mr. Dykshoorn was buried with his “divining rod,” a thread of piano wire that served, as he wrote in his book, “as an aid to my concentration” during case work.

–Matt Flegenheimer, Marinus B. Dykshoorn, Psychic, Is Mourned in Bronx, New York Times 10.10.11

Many systems of clairvoyance involve the observation of a delicate apparatus–a thin wire,  a stream of smoke, a candle flame or the hiss of white noise–which exists in a borderline state and is thus highly sensitive to the influence of forces both seen and unseen. The non-linear feedback loop between a loudspeaker, microphone and high-gain amplifier circuit responds dramatically to minute changes in its immediate environment, fulfilling the requirements of both a potentially chaotic system as well as the needs of the would-be psychic investigator.

The Ghost Locket Triptych was created between 7-11 October 2011 in Aarhus, Denmark for a battery-powered seance executed by Derek Holzer and Kristian Hverring on the evening of 12 October. These lockets use locally-sourced materials embodying certain historical resonances noted by the artist during his stay here. Internally, each locket contains a hand-built Germanium transistor distortion circuit, a 1/2 Watt audio amplifier, a small speaker, a source of illumination and an antique photograph–the ghost within each machine.

The artist remains indebted to a series of conversations with the estimable Mr. Martin Howse of London and Berlin for inspiration in these and other matters.

The three elements of the Ghost Locket Triptych will be available for sale individually or as a set following the performance in Aarhus. THE EDITION IS SOLD. Please contact the artist for more information.

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“nonlinearity I” video + SoundBoxes in Brussels

Posted in Announcement on November 7th, 2010 by admin

nonlinearity I

nonlinearity I from macumbista on Vimeo.

After touring 3 weeks with 25 Kg of heavy metal synthesizer in a suitcase, I came home wanting something a bit lighter and simpler. My back-to-basics approach uses one SoundBox built for workshops with gypsy children and Afghan refugees in Hungary a few months ago, one contact mic, a Germanium transistor distortion pedal and 10 years worth of found objects collected on trips around the world.

At the heart of this video lies the concept of nonlinearity, that most basic building block of chaos theory and the wonderful complexities of our natural world. The microphone/speaker loop forms a system into which the nonlinear irregularities of 9V electronics, beads, springs, moss, shells and bits of bone produce unique bifurcations and attractors. Shaking things up a bit resets the system and new chaotic patterns begin to emerge…

SoundBoxes in Brussels

Three Neanderthal Electronics works of mine will be shown as part of the moddr_* showcase at iMAL in Brussels this month:

* BlueLightSpecial (2009)
* SoundBoxOne(“handmade”) (2010)
* SoundBoxTwo(“indianblanket”) (2010)

The show runs 13 November – 12 December 2010 and also features far more computer-oriented works by Gordan Savicic, Danja Vasiliev, Walter Langelaar, Julian Oliver, Martin Howse, Jonathan Kemp, Matt Kemp, Philip Lammer and Florian Cramer.

asbl iMAL vzw – 30 Quai des Charbonnages/Koolmijnenkaai 30 – 1080 Bruxelles/Brussel 1080
Opening on Saturday 13th of November, 15:00 – 23:30
with moddr_ workshop and performances, check the complete program! Finissage on Sunday 12th of December.
Opening hours:
Wed > Sat, 12:30 – 18:30. Free admission

BlueLightSpecial + SoundBoxOne("handmade")


Thanks to Walter Langelaar for the invitation!!!!

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Chaotic Colorfields

Posted in Text on August 14th, 2010 by admin


The Chaotic Colorfields performance exploits the psychological intensification which pulsed light adds to the audience’s perception of a sonic event, as well as the physical effect upon the receptors of the eye created by contrasting colorfields. Four colored strobes are directly driven by a self-built analog synthesizer set up to calculate a variety of chaotic feedback systems. Louder than bright and brighter than loud.

Upcoming Performances

EDIT: I’ve decided to postpone this one a bit, to spend more time on making it the best it can possibly be. Upcoming shows in Den Haag, Budapest and Aalborg will be solo improvisations for self-built analog synthesizer without the strobes…


* Self-built Analog Modular Synthesizer w/ Light Controller Module
* Stereo or Quadrophonic (preferred) PA System
* Four 1500W or brighter DMX Strobelights, each with one Color Filter (Red, Green, Blue, Yellow/Orange)
* Smoke Machine
* Total Darkness


Chaotic Synthesis

Chaotic systems are deterministic dynamic systems that have a high sensitivity to initial conditions. Only dynamic systems that include a nonlinear feedback path are capable of chaotic behavior. Common examples of chaotic systems include coupled pendulums, pseudorandom number generators, and the earth’s weather system[…] Nonlinearity and feedback are necessary conditions for the existence of chaotic processes.[1]

The Colour Out of Space

The colour, which resembled some of the bands in the meteor’s strange spectrum, was almost impossible to describe; and it was only by analogy that they called it colour at all…

…as the column of unknown colour flared suddenly stronger and began to weave itself into fantastic suggestions of shape which each spectator described differently, there came from poor tethered Hero such a sound as no man before or since ever heard from a horse[…] That was the last of Hero till they buried him next day.[2]

Imaginary Colors

Non-physical, unrealizable, or imaginary colors are points in a color space that correspond to combinations of cone cell responses that cannot be produced by any physical (non-negative) light spectrum.[3] Thus, no object can have an imaginary color, and imaginary colors cannot be seen under normal circumstances. Nevertheless, they are useful as mathematical abstractions for defining color spaces.[4]

Perception of Imaginary Colors

If a saturated green is viewed until the green receptors are fatigued and then a saturated red is viewed, a perception of red more intense than pure spectral red can be experienced. This is due to the fatigue of the green receptors and the resulting lack of their ability to desaturate the perceptual response to the output of the red receptors.[5]

Color as Subjective Experience

In a viewer’s experience, the perceptual interpretation of the context is expressed in the color itself; we usually cannot, or only with unreasonable effort, separate the “real” color from its context. In particular, we are normally completely unaware of the “cognitive” aspects of color perception — discounting the illuminant, spatial perspective, shadows, memory, object concepts, available color labels, and so on.[6]

[1]Slater, Dan, “Chaotic Sound Synthesis”, Computer Music Journal 22.2 19 September 1998, pp 12-19.
[2]Lovecraft, H.P., “The Colour Out of Space“, “Amazing Stories” September 1927.
[3]MacEvoy, Bruce, “Light and the Eye”,
[5]Lindsay, Peter and Norman, Donald, “Human Information Processing,” Academic Press, 1972, pp 196–216.
[6]MacEvoy, Bruce, “Basic Forms of Color”,

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Testing for Chaos

Posted in Announcement on August 9th, 2010 by admin

The following are tests of the chaotic synthesis system I’m working on, and in no way should be considered “finished pieces”:



Modules used in these recordings:

Thomas Henry XR-2206 VCO (Bugbrand PCB layout)(VCO range)
Thomas Henry XR-2206 VCO (Bugbrand PCB layout)(LFO range)
Ian Fritz EZ Chaos (Uncle Krunkus stripboard layout)

In the first example, chaos01.mp3, the triangle waveform of the LFO drives the EZ Chaos. The Z (marked NL on schematic) output of the EZ Chaos drives the 1V/Oct input of the VCO. Both Drive and Rate pots are set about at the middle, and the Damping is totally turned down. As you can hear, it maintains a very steady modulation. The changes in modulation pattern only come from my manually adjusting the LFO.

In the second example, chaos02.mp3, the poti settings and routing remain the same from chaos01.mp3. However, I have routed the Y output to the Linear FM of the LFO, and the X output to the Exponential FM of the LFO. The modulations become much more chaotic in this setup. Through the clip, I adjust the depth of the LinFM, ExpFM and the general rate of the LFO. Better, don’t you think?

For me, the modulation patterns in chaos01.mp3 sound to me like a non-linear transfer function, but don’t sound chaotic at all in the sense that the transfer function remains almost identical for every cycle of the LFO at any frequency tested.

My understanding of chaotic synthesis usually involves feedback between at least two–but in my experiments up to 8–cross-modulated VCOs with a non-linear function in the feedback loop. The results tend towards certain attractors, but every cycle is distinct from the previous one, even if after 3 or 7 or 15 cycles you might return to a common origin.

Assuming that my EZ Chaos circuit functions as it should, the benefit I see out of it would be the ability to make chaotic patterns from a single LFO through the feedback. Normally I would have to use 2 or more LFOs to get the same kind of chaotic oscillations.

However, by itself I don’t hear chaos coming from this circuit, only non-linearity. It’s the feedback in chaos02.mp3 that makes it chaotic for me. Looking at a double well attractor on the scope is one thing, but hearing it is the proof…

Updated info on the chaos circuit as well as some tuning tips can be found on the Elby Designs page for their ED108-ChaQuO module.

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Analog Multiplier Module

Posted in Documentation on August 3rd, 2010 by admin


This synthesizer module allows “Buchlidian” style processing of three input voltages. It can do much of what the original Buchla 257 Voltage Processor does: addition, subtraction, multiplication and division. The only feature of the 257 it lacks is the ability to “transfer control” (i.e. interpolate) between the two different applied voltages

It contains one section with three attenuverting/bipolar inputs, which allow the user to sweep between the original signal on the right hand side of the potentiometer and an inverted version of the signal on the left hand side, with no signal passing through at the middle position. An offset control is also present to add a fixed DC voltage to the signal.

The other section contains an analog multiplier with three inputs, X, Y and Z, each hardwired to one of the attenuverting outputs. Output is calculated as follows:

W out = ((X1 – X2)(Y1 – Y2)) / 10V + Z

The panel contains two of each section. The X and Y inputs can be switched between AC and DC coupling, with an AC breakpoint of approximately 0.2 Hz, while the Z input is always DC coupled.


Tom Bugs described himself as a magpie to me once in regards to his circuit designs, and while working on this module I have followed his lead. The “attenuverter” sections were designed by Chris MacDonald and modified by Peter Grenader, and have been further developed by Matthias Herrmann/Fonitronik.

Likewise the analog multiplier section is really just bringing every feature of the AD633 4 quadrant multiplier chip to the front panel, with some inspiration from Roman Sowa’s Ring Modulator design, as well as Marc Bareille’s adaption of that same design.

[click schematic to enlarge]


The AD633 documentation shows different applications such as simple multiplication, squaring and division as well as more complex tasks such as a linear Voltage Controlled Amplifier as well as 6dB/Octave Voltage Controlled Filters and a Quadrature Oscillator (both not shown here). The most common sonic use of this IC is for ring modulator circuits.

However, my main application for this is the creation of different kinds of transfer functions for use in chaotic synthesis. I discovered how useful the analog multiplier is while experimenting with the Doepfer system at KHM in Cologne. Multiplying two oscillators through a ring modulator, sending the result to modulate the first oscillator and using the first to modulate the second created an amazing array of unpredictable but certainly far from random results.

In most applications shown in the datasheet, the X and Y offset pins are grounded. But while breadboarding, I discovered that the X and Y offset gave a higher level of control over the modulations, so I built them into the panel. Likewise, switching between AC and DC coupling alters the resulting sound immensely, with the best results coming from one signal being AC coupled and one being DC coupled.

Adding one of the X or Y input signals to the Z input creates a kind of VCA which strengthens the effect. Or using another signal, such as a Low Frequency Oscillator with some suitable gain and offset, adds another modulation source into the mix to provide anything from amplitude modulation to clipping.

I believe this module gets at just about any type of processing the AD633 can do, as most of the time there is no attenuation, inversion, Z input or any kind of offset available on a normal ring modulator or analog multiplier.

Sample Applications from the AD633 Datasheet

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Prototyping/Analog Computer Modules

Posted in Documentation on July 30th, 2010 by admin

I’ve been having some great correspondence with Jason R. Butcher about Buchla synthesizers, analog computers and chaotic synthesis techniques. He reminded me of a very special version of the Buchla 200 Music Box, created by Don Buchla for an electronics and cello work by Ami Radunskaya called Sili-Con Cello in about 1978 or 1979.

One of its features was a breadboard prototyping module, seen in the upper left corner. Here, Buchla created custom circuits to respond to the performance gestures of acoustic instruments in the era before Pure Data or Max/MSP.

[Photo from The Audities Foundation]

Jason showed me his own version of the breadboard module, which just happened to look a lot like a panel I spec’ed out last night. Here’s the completed module mounted in the case this afternoon. Each panel component (potentiometers and banana jacks) is routed to the terminals (the green areas), which in turn can be jumpered anywhere on the breadboard.

My first task with this module will be to design a “Buchlidian” style control voltage processor. It will contain one section with an attenuverting/bipolar input with offset and another section with an analog multiplier. The panel will have two of each section. It can do much of what the original Buchla 257 Voltage Processor does: addition, subtraction, multiplication, division…

The only thing it won’t be able to do is the “transfer control” (i.e. interpolate) between the two different applied voltages (although this could probably be done with a pair of Voltage Controlled Amplifiers rigged up as a cross-fader).

This new processor module represents one section of a larger analog computer project I plan to use for developing new chaotic synthesis techniques. The other sections would be a set of integrators (planned), an analog logic section (completed) and a suite of tools for working with digital pulses (comparators, clock dividers, digital logic and digital noise–all planned).

Of course, this prototyping module could also be used to lay out other kinds of non-linearizing functions to stick in the chaotic feedback paths. I’ll document those as they come up.

Discussions over the last year or so with Martin Howse continue to remind me that analog computers evolved out of the V2 rocket program and were mainly designed to control the flight path of missiles. In fact, just about anything used in electronic music has some sort of seedy military past. Our art is nothing more than a byproduct of the quest to more accurately drop bombs on each other, something I’m sure both Stockhausen and Kraftwerk were acutely aware of…

As for Mr. Butcher, check out his wild, live analog synthesizer project with Don Hassler. Buchla 200 Music Box vs EMS Synthi A, highly recommended!

Hassler/Butcher, Eyedrum, Atlanta 31.03.10

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