A Look at Performer/Machine Interaction Using Real-Time Systems
Cort Lippe · University of Michigan Library Repository · 1996
This paper examines the utilization of the computer as a musical tool. In particular, the relationship between performers and interactive computer music systems involving real-time digital signal processing is explored. The question is posed: as a musical tool, does the computer have a unique functionality? 1 Sound Processing and Time Delay Disregarding questions of latency based on hardware limitations, most real-time processing and analysis necessitates the storage of sound samples, either for later playback or as analysis data, thereby producing a time delay between the original signal and its transformations. Reverberation, flanging, chorusing, filtering, etc., are obvious examples of signal processing algorithms which make use of delayed copies of a signal. Pitch tracking, and FFT analysis-resynthesis make use of a delayed (stored) signal copy. Envelope following makes use of a low pass filter (calculated with past samples), and harmonizer algorithms store small windows of sound. (Ring modulation appears to be one of the few processing techniques that does not necessitate delay.) Samples recorded on-the-fly for later playback must be stored, as do pre-recorded samples stored either on disk or in memory. Thus, almost anything outside the realm of sound synthesis (FM, AM, etc.) that takes place in a live, interactive computer music environment involves some sort of time delay. [Jaffe, 1995] (And performer input used to control pure synthesis introduces a time delay in the synthesis’ control structure.) Does this seemingly inherent delay define a particular relationship between performers and computers? 2 Performer Input/Machine Response Metaphorically speaking, a performer often leaves audible traces “in the air” during a real-time computer performance as the music moves forward in time. A common observation—sometimes a complaint—is that real-time computer music has a static performer/machine relationship, one in which the computer always reacts to or transforms material generated by a performer. (The same critics note that the performer/machine relationship often seems less static in the tape/instrument repertory.) Real-time transformations of an instrument, using the instrument's sound as input to the transformational process, cannot easily avoid a kind of “call and response” relationship. 2.1 Transformational Processes Is this call and response relationship a musical trap? A great deal of music employs some kind of repetition of materials: echo is the simplest form of delay, and call and response is common in many kinds of music. In addition, as a temporal art-form, a large body of music is organized around techniques such as imitation, diminution, augmentation, transposition, inversion, and retrograde (albeit, usually of the parameters pitch and/or rhythm). This incomplete list of techniques describes transformational processes which are based on repetition, and quite often, in practice produce audible delayed responses or reactions to some original material [Rowe, 1993]. (Contrary to this, the majority of story-telling, poetry, and theater utilizes vastly different methods of organizing materials. Perhaps, if music were a “language” in any sense like natural languages, techniques like diminution or transposition would not be as commonplace in music.)