Filtering, the process by which specific components of an audio spectrum are amplified at the expense of other portions of the spectrum, forms the basis for virtually all of the signal processing techniques employed in OverTime. This decision grew out of an early group discussion, in which we examined the application of amplification to our respective disciplines. Both visual art and music employ filtering on a very elemental level -- that is, all colors can be produced by filtering white light, and in theory all sounds can be produced by filtering white noise. Dancers, it was proposed, filter an empty space by amplifying parts of that space through their presence.

Proceeding from this basic analogy, we attempted to abstract the principles of the filter to a vocabulary equally applicable to movement, sound, and visual art. We hit upon the idea of a suit, designed by the visual artists, which could be worn by the dancers. The components of the suit, along with set pieces of the same material, would inflate or deflate in response to the movements of the dancers. While the dancers controlled the level of inflation in the suit, the status of the suit would determine the range of movement available to the dancers at any given moment, thus creating a feedback loop. This would filter the movement of the dancers, amplifying certain movements and attenuating others by focusing the attention of the audience on specific sections of the physical space, just as actual filters direct attention to a specific area of the visual or auditory spectrum

While the suit will not be complete in time for our workshop performance, we will be presenting prototype versions of the corresponding audio signal processing tools. These tools have been designed specifically with the suit in mind, as the control parameters for both the audio and the suit will correspond directly in the solo performed by Malene Schjønning (VIDEO CLIP?). Over the course of the solo, Schjønning will explore three different approaches to filtering sound, each of which can be mapped to spatial considerations.

In the first of these, Schjønning controls the first nine partials of the overtone series for four pitches, determined by the composers. She can choose which portions of the audio spectrum to amplify, and which to attenuate. The choices she makes, however, directly affect only one of the four voices. While the filtering of the other three voices is dependent upon her control of the first voice (at this point directly so), ultimately the amplification of a given partial in these three voices will be controlled algorithmically, based on the information that Schjønning provides in the course of her performance. For the second approach, Schjønning will control the parameters of a resonant band-pass filter. Although the source sound is a simple buzz, the filtration creates a chiming effect, which Schjønning can manipulate. The third approach explores filtration in the form of phase cancellation. Schjønning controls the frequencies of two sine tones which, through additive synthesis, cause periodic beating. Schjønning's movement determines both the frequency of the beating and the pitch.

In the duet of Liz Pearlman and Diane Torba (VIDEO CLIP?), each dancer will control aspects of the signal processing. Pearlman will have total control over the gain and the bandwidth of an infinite impulse recursion filter, which will process a violin part played by Maja Cerrar. An interaction somewhat akin to a tug-of-war between Pearlman and the computer determines the center frequency of the filter. The sound processed by Pearlman is further manipulated by Torba, who controls two parameters of a granular synthesis program, which divides the sound into small chunks and rearranges it, according to the control data provided by Torba.

nicholas@music.columbia.edu