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Rungler • Chaotic Sequences | jvkr •• blog

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Rungler • Chaotic Sequences

This story starts with a visit, one day, to the studio of Rob Hordijk, who had been approached to do repair works on some of Sonology’s vintage devices. Apart from this repair business, and of more interest, Rob constructs modular synthesizers of his own design. He is also known for having been a member of the Nord Modular development team.

That day, with a colleague, we drove to his studio, here in The Hague, to pick up the repaired modules. It was my first time meeting Rob. After explaining about all the replaced potentiometers and other repairs he had done, he enthusiastically started talking about the rungler, and let me try out a device called the Blippoo Box.


In order to understand what this is about, here is an explanation that he himself posted on a forum:

“The rungler is basically a CMOS shift register clocked by one oscillator and receiving its data input from the other oscillator. In the Benjolin the last 3 stages of the shift register form 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'. To describe the rungler waveform in similar terms as like a sine wave or pulse wave I call it a 'stepped havoc wave'.”

The Blippoo Box, as I understand it, is quite similar to the Benjolin, the latter being slightly simpler. With only two oscillators and 12 controls, I thought the sounds produced by the Blippoo Box to be rather astounding. Especially the chaotic patterns sounded very interesting. The oscillators in combination with the rungler, behave like wave generator and step sequencer, but intertwined in a very unique way. The oscillators control the rungler, and the outputs of the rungler, based on the state of the oscillators, control their speed.

Again Rob explains:

“The purpose of the rungler is to create short stepped patterns of variable length and speed. One could categorize the circuit somewhere halfway between a plain S&H and a shiftregister-based pseudorandom generator. 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 result is a structure in which every control influences the sounds and patterns on a fundamental level. The variety of sounds that can be produced is impressively large, given the fact that there are only two oscillators. Playing becomes more an act of discovery, rather than precisely controlling the instrument.

And—of course—when encountering such an interesting idea, the first thing that comes up in my mind is, whether it would be possible to program this in DSP. So here is my attempt at creating stepped havoc. This was all done in gen~, within Cycling74’s Max program. The filters are based on a description of Moog ladders, that I came across recently. And I took the freedom to introduce some additional control. I tried to limit as much aliasing.

In order to have good control, I use the new Mira application on iPad. Like this it is possible to play with multiple parameters simultaneously.

The video below is an overview of the options, more than a performance. Moreover, I need some time to spend with the instrument in order to fully grasp the scope of possibilities. I might use this in a next performance. The full range of the audio spectrum can probably be best enjoyed with headphones, rather then using the built-in computer loudspeakers. Don’t set the level too high, though.

On the downloads page you find a max patch, that shows the basic implementation of the rungler.


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