Aleatoric music is chance music... music that is somehow composed without our knowing or intention. Like the notes of wind chimes or the patterns of rain on the roof.

Circuit bending turns certain keyboard instruments into superb aleatoric music generators capable of producing fascinating chance music. Reed calls these bent keyboard instruments Aleatrons.

More from Reed's EMI article on the SA2 Aleatron:

"All fields have their hallmarks. My experience with circuit-bending has, over a period of thirty years, resulted in the development of several distinct technical categories born of the process, each best represented by a specific instrument or two. These main categories would include body-contact control, human voice synthesis, digital samples, the equal-tempered scale and, lastly, aleatoric instruments. That is, chance composition devices. I've come to call instruments that produce aleatoric music through the electronic process of circuit-bending aleatronic instruments, or the result of aleatronics.

"But how about an instrument that stretched beyond single category and represented the entire scope of circuit-bending's possibilities? An instrument that involves body-contacts, human voice synthesis, digital sampling, the equal-tempered scale and automatic chance composition. All, present and in fine example. That would be a true hallmark instrument.

"Such an instrument exists. This instrument is the Casio SA-2, a small 32-note keyboard with a large set of built-in sounds to work with. There are thirty-two accompaniment patterns for circuit-bending to reshape. These include seemingly sampled percussion instruments whose high-quality recording really shines through, adding a sparkle of live performance to the countless (re)arrangements now obtainable. A bank of sixteen instrument voices is also provided. These may or may not be sampled. They are, however, high-quality voices, most with rich overtones. While the keyboard is described as only 2-note polyphonic, circuit-bending seems to change all this. In fact, very complex pitch clusters and orchestrations result from the new anti-theory electronics.

"A single push-button trigger switch and body-contact are sufficient to nudge the SA-2's programs into wondrous disarray, resulting in original composition sequences looking to the five categories above... "Here the body-contact, rather than implementing pitch-bend or other frequency shaping as is its function in many other circuit-bent instruments, is used to advance the aleatoric musical structures. A delicate touch upon the brass contact increments the rhythmic and tonal frameworks at the heart of the chance compositions, continually pushing them forward into new combinations of indeterminate events.

"In the realm of human voice synthesis ... no, the SA-2 does not come supplied with such capabilities. Still, on a number of occasions, startling human-like vocalizations arise. Murmurs, chants, shouts and odd singing might materialize and disappear as the music evolves. The emotive effect of these shadowy utterances can be powerful and revealing ... a Rorschach image in sound.

"Digital samples are fascinating to dissect under the diffracted light of circuit-bending. As mentioned before, the SA-2's percussion sounds seem sampled, and all voices involve a digital capture scheme that has them nicely rendered in accessible sound files (probably Pulse Code Modulation).

"Whereas analog signals tend to deteriorate into static-like decay when exposed to certain circuit-bending applications, digital signals break-down into distorted routines rather than distorted tones. The tones can therefore remain sharp while their harmonic content, envelope and assembly behavior is altered. Likewise, just as it is with the musical notes, digital percussion sequences are similarly transformed. Cymbals become backward gongs, kick-drums blend into bass lines, snare drum decays are frozen into crystalline seas of sizzling metallic hiss.

"Generally, keyboard instrument = equal tempered scale. The very nature of circuit-bending places it in the opposite corner of this scheme of order, from conceptual foundation to vocalizations. Perhaps this is why the combination of the two conflicting sensibilities can be so catalytic. Here, within the circuit-bent SA-2, there is created a riveting interface between these two disparate worlds, elements of the familiar bound together by an invasive disorienting matrix.

"As mentioned, central to prompting the SA-2's electronics into unique tonal synthesis and aleatoric music production is a push-button triggering switch, the most important circuit-bending addition. This switch disrupts the instrument's program routines. Several choices exist as to where to connect the switch to the circuit. Any of these will initiate aleatoric composition. In use, with or without keyboard keys being held down, and with or without a rhythmic accompaniment playing, the musician quickly and lightly taps this push-button switch while listening to the results.

"Any number of things may happen. The entire circuit may crash. Silence. No response anywhere until the main power switch is turned off and back on. More than likely, the keyboard will become inoperative while the sound circuit, cautious of the strange knock, decides whether or not to answer the door. Many knocks might go unanswered. But when this obscure door does open to the world of anti-theory electronics, I've learned that anything might appear.

"It could be a haunting voice, a single note of beguiling texture perfect for capturing as a sample and flying into a full polyphonic keyboard system. Abstract sounds might come forth ... tangles of sustained noise and pitch with evolving tonal clusters buried within.

"Pushing the switch might cause a loop to begin. This loop could be percussion instruments revolving in odd rhythm, abstract sound cycles, musical notes repeating a melody, or combinations from dense to sparse of all elements working together. These repeating sound-forms may slowly fade away, hold steady or accelerate to crescendo.

"Pushing this digital trip-wire will also, every so often, launch an aleatoric episode such as those described before. This chance composition, like certain loops, may also slowly accelerate to crescendo ending in any number of resolutions including tone clusters, silence, loops, pre-programmed rhythms or, occasionally, a new aleatoric sequence possibly again increasing in tempo through another complete cycle. The keyboard may or may not be active during loops and aleatoric passages. If so, it may or may not behave as usual, sometimes pulsing disassociated notes, producing sound effects or even modifying accompaniments in progress.

"Pushing the same triggering switch during aleatoric progressions can shift elements within the music, altering perhaps the percussion pattern, the choice of lead instrument, the accompaniment scheme or a number of other sonic aspects effecting the flow of indeterminate composition. Again, pushing the button represents a certain degree of risk, not at all unfamiliar to circuit-bending, that could result in program crash. While it's true that the lost sound-form is probably gone forever, impossible to achieve in exactly the same way again, the bending process balances this out here and in many other instruments by providing a bottomless well of possibility for yet unheard musics, a chance to give life to new and unique sonic creations every time the circuit is turned on."

The standard SA2 Aleatron contains the additions of a trimmer dial (for setting the intensity of the triggering pulses), a specialized short-throw trigger button (for initiating aleatoric passages), two body contacts (for incrementing aleatoric passages), a blue LED power light behind a vintage milk-glass-in-brass pilot lens, a speaker switch (for turning on and off the internal speaker), a reset switch (for crashes), and a gold-plated RCA output.

The instrument is finished in fluorescent green crackle with a dusting of iridescent powder under the final gloss.

The SA2 Aleatron is a wonderful example of the power of circuit-bending and results in a truly fascinating chance music engine.

Click the image below for deep-end SA2 Aleatrons.


Price is $800 plus shipping. This instrument is available as a Bare Bends model also. See the Bare Bends Gallery...



POB 20181
Cincinnati, OH 45220