Macumbista Benjolin 2013v2–now taking orders

Posted in Announcement on June 4th, 2013 by admin

The Benjolin is a standalone synthesizer designed by Rob Hordijk from the Netherlands. It contains two oscillators (one LFO and one VCO), a low pass filter and a circuit called a “Rungler”, which allows chaotic cross-modulation possibilities between the different parts of the circuit. Hordijk refers to the Benjolin as a circuit which has been “bent by design.”

These hand-made Macumbista Benjolins have been further customized with a patchbay, which can be used to interface with other modular synthesizers, or to setup further feedback systems within the Benjolin itself, a switchable external line input to the Benjolin filter and LEDs displaying the internal state of the Rungler.

For Spring 2013, I will produce five of these Benjolins, housed in antique wooden slide/dia boxes. One Benjolin from this run has been sold, and four more are available for order, with shipping on or before 21 June 2013.

This run is sold out!. These Benjolins are produced under licensed agreement with Rob Hordijk.

This instrument ships with an external 110V or 220V AC/AC converter wall power supply.

Please email MACUMBISTA at the domain GMAIL dot COM with orders and inquiries. Other customizations are available on request. Thank you for your kind attention.

AUDIO DEMOS

Quick and dirty demo of Benjolin 2013v1, the first of several Benjolins to be built for sale in 2013.

A familiar old loop run through the filter section of the Macumbista Benjolin2013v2 via simple line-in modification. Filter cutoff frequency modulated by hand, by the two oscillators and Rungler sections of the Benjolin and by various control voltages available from the banana-jack patchbay.

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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.

http://institutet.eu/productions/we-love-africa-and-africa-loves-us/

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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
n = 5 : ABAABABAABAAB
n = 6 : ABAABABAABAABABAABABA
n = 7 : ABAABABAABAABABAABABAABAABABAABAAB

(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.

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oren ambarchiaudience of one[2012 touch]

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