From the Explanatory Notes of Visual Music Studies, Volume 1 - Pythagoras & Pellegrino In Petaluma - of the Visual Music Studies DVD Series by Ron Pellegrino, composer:
The visual images are produced by a specially designed electromechanical optical system - very light-weight mirrors superglued to small posts on galvanometers. Galvanometers are small motors that translate the electronic wavetrains of a synthesizer to mechanical vibrations. The vibrating mirrors are positioned to provide deflection of a laser beam along the x and y axes and then to project the image out onto a screen or other reflective surface. My laser animation system was configured so each galvanometer had a different frequency range as well as different sets of resonant frequencies so the system as a whole would behave much like a music instrument, in this case a visual music instrument. This is a system I designed in 1974 to replace the work I had been doing since 1967 with music synthesizer generated oscilloscope images. From1971to 1973 images from the early oscilloscope system were translated to a set of 16mm films, a set called the Lissajous Lives Film Series. The oscillographic films were used in a variety of ways - as dynamic graphic scores to be interpreted by performers on any combination of instruments and as set pieces with composed scores including both electronic and acoustic instruments.
For the material on these DVDs, the synthesizer generating the wavetrains is a Synthi AKS, an early 1970s hybrid synthesizer with analog wave functions and a digital keyboard. The tuning of the synthesizer's wave functions is done by hand control via potentiometers addressing the various wave functions. The hand controls include highly sensitive five-turn potentiometers for fundamental frequencies and the low-pass filter cutoff frequency, less sensitive one-turn potentiometers for amplitude, waveshape, phase, and mixing, and a scalable two-axis joystick that can be patched to control any wave variable.
The laser images are drawn out in time by a deflected point of laser light following paths prescribed by the interaction of the stereo wavetrains driving the mirrors via their galvanometers. In perceptual terms the physical creation of the forms is based on the persistence of vision, a psycho-optical phenomenon characteristic of the human seeing system that sustains an image for a short time after its cause is removed. It's not much of a challenge to tune to the human seeing system because I just rely on my own seeing system figuring that most interested parties, given even a short learning curve, will see much of what I see especially when I guide their eyes in demonstrations. However the video seeing system presents special problems because rather than taking the visual information in a continuous flow it breaks it into 29.97 frames per second. Furthermore, each of those frames is made up of two fields which can be thought of as sub-frames that address alternately the odd and the even lines of the video screen, a process that's called interlacing. So an initially unbroken laser flow becomes chopped by the video recording system into frames and fields and that chopping presents two separate frequency obstacles (around 30 Hz, the frame rate, and 60 Hz, the field rate). Those obstacles or limitations must be factored into the design of acceptable images. The point is that given all the restrictions of a video seeing system - frames, fields, aspect ratio, screen size, all the variables connected with light generation which includes dot size, phosphors or liquid crystals, etc. - it's important to remember that the images that finally make their way to a DVD are a relatively small sample of what's possible with my laser animation system in a full size projection mode. Despite the limitations of media translation there's much to be learned about visual music from the contents of a DVD.
The physical limits of this particular laser animation system are defined by the frequency ranges of the galvanometers, the use of an off-the-shelf audio power amplifier to drive the galvanometers, and the nonlinearity of the galvanometers that results in a number of highly responsive resonant frequencies as well as gradual dropoffs in response at the lower and upper ends of the frequency range. Within those physical limits full use is made of the various electronic wave modulation types including amplitude, frequency, waveshape, and phase modulation.
As a visual music instrument the laser animation system has served a variety of presentation and performance functions - sometimes solo especially in the demonstration mode, sometimes in ensemble with other performance artists including musicians, dancers, and light artists, and sometimes being picked up by a video camera and routed to a computer for real-time processing and video projection.
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