bret battey • bat hat media



installation for computer-controlled sound and electromechanical video-feedback filter (2000)


Uroborous is a study in the synthesis of simple feedback systems, abstract audiovisual composition, and the idea of compositional "gesture." I created it at the invitation of Seattle's Jack Straw Foundation for installation in their Media Gallery.

The wager of the design was that linked audio and visual feedback processes could create continually transforming audio/visual gestures, and that these gestures would be of interest to human perception due simply to the intrinsic nature of the processes involved.

I was, in fact, able to tune the system so that it imparts, to me, a mysterious character of "aliveness" and expressiveness to what is "merely" abstract sound and light.

This resultant behavior of the system leads to the title of the work, uroborous being the archetypal image of the serpent consuming its own tail. In this case, I consider the uroborous to be symbolic of the feedback processes that are an essential part of phenomenon from the growth of organisms to the formation of social structures and the shaping of galaxies.

My intent is that Uroborous should give rise to fascination, wonder, and contemplation. As novelist Charles Baxter writes:

Wonder is at the opposite pole of worldliness, just as stillness is at the opposite pole from worldly action. Wonder puts aside the known and accepted, along with sophistication, and instead serves up an intelligent naiveté.

Technical Details

The Jack Straw Media Gallery's Macintosh G3 Computer runs a master control program, audio synthesis program, video analysis, and the video filter.

Electromechanical Video Feedback Filter

The Electromechanical Video Feedback Filter provides a computer-controlled extension to classic video feedback technique. Small servo motors control the position of the video camera and of two wire mesh screens suspended in the feedback path. The mesh screens create moiré interference patterns in the feedback path. The TV monitor settings are carefully tuned cause oscillations of color in response to the feedback flow.

The Feedback Filter utilized the Mini SSC II(TM) Serial Servo Controller by Scott Edwards Electronics, Inc. The Mini SSC allows one to easily control up to 8 hobby servo motors with a simple serial connection (Mini SSC's are chainable for up to 255 servos).

Connecting a Mac serial port to a Mini SSC:
Details of connecting to a Macintosh serial port were not provided in the instructions, so I had to hack a cable. The trick is this: the Macintosh 8-pin round serial port (a DIN-8 style plug) is RS-422 rather than RS-232. Therefore it has both a positive signal transmit (on pin 6) and a negative signal transmit (on pin 3). To map to an RS-232 port, one needs to use only the negative signal transmit. All you need, then, to talk to the SSC II from the Macintosh is: get yourself a Macintosh serial cable (for modem or otherwise), and hack off the non-DIN-8 end. Use a continuity tester to figure out which wires correspond to Pin 3 (positive transmit, a.k.a. TX+) and Pin 4 (signal ground, a.k.a. GND). Connect the TX+ wire to the green wire in a phone cord and GND to the yellow wire.
Most new Macintoshes don't have serial ports, providing a built-in modem instead. A simple and inexpensive solution was the Griffin gPort.
Note that the Mini SCC doesn't come with a power supply - you have to buy that separately, as well as a separate power supply for your servo motors. The Scott Edwards web site provides a FAQ, including recommended power supplies.
I purchased my Mini SCC and a pack of 6 HiTek hobby servos from the Robot Store.

For the camera, I used an X10 Xcam2. It is relatively poor image quality -- not very bright -- but in this case that is an advantage because it provides unique coloration results.

Audio Synthesis

The sounds are synthesized using a technique I have developed which I call Compressed Feedback Synthesis (CFS). It is based on the type of feedback you get when a microphone is too close to a speaker. Essentially, it inserts dynamic controls into the feedback loop that prevent feedback from going out of control. For sound synthesis buffs: It essentially is a comb filter modified with amplitude compression and pitch shifting. CFS is implemented here in the programming language SuperCollider.

Video Analysis

The computer analyzes the flow of images created by the Video Feedback Filter using a video capture card and David Rokebys softVNS video analysis system. Though softVNS is capable of fairly complex analysis of the video image, for Uroborous it is simply returning a measure of the amount of motion occurring in the left and right halves of the image.

Control Program

Master control of the system is programmed in the MAX language from Cycling74. The program is always slowly shifting the position of the servo motors in the Video Feedback Filter and the basic parameters of the audio synthesis. Meanwhile, it observes the data returned by softVNS and responds by altering the rate of change of the servo motors and sending appropriate controls to the audio synthesis program. MAX communicates to SuperCollider via MIDI command piped over a MIDI IAC (Interapplication Application Communication) port provided by the Opcode Midi System.


Click the thumbnails for full-sized images