an evolutionary sound process designed by Tim Perkis

First performance at the Exploratorium, San Francisco, July 31, 1994. 

  Rasamudra explores the possibility of making music by simulating 
the process of biological evolution. In my recent and current work, I 
have been using genetic techniques to develop "wild" systems of 
interaction. The principle is astonishingly simple: one generates a 
population of random computer programs (written in a special 
language which limits the damage malformed program can do), and 
tests them all, chopping up and recombining in a random way the 
better performers in the population; these new programs are tested 
in turn, and the process is repeated. Amazingly enough, useful and 
correct programs emerge quite quickly. This process in effect mimics 
the process of biological evolution which proceeds through sexual 
  In Rasamudra, the programs each generate a musical phrase; over 
the course of an afternoon three performers grade each program on 
how well they like its phrase, as well as indicating one of six 
emotional states (or rasas) that the phrase suggests to them. Each 
performer's judgement is sent to the computer/composing system 
through foot pedals, as well as communicated to the other 
performers by hand gestures.  The resulting piece of music is built 
using this phrases, which all end up in a certain family resemblance, 
sorted by rasa.      
   Over the course of the performance, a structure emerges in the 
music, through the interaction of chance and judgement: likewise, a 
structure of understanding and consensus emerges among the 
players, as they develop a language of hand gesture to communicate 
their perceptions to each other.

Hardware for Rasamudra. 
 Two performers made judgements and indicated their degree of confidence in the 
judgement with the analog foot pedals; the third performer pressed a 
footswitch corresponding to one of the rasas to indicate the group 
judgement to the computer.
The computer would then assign this "grade" to the currently playing 
phrase, and generate a new phrase in the same rasa by breeding 
together randomly selected phrases from the population. Preference 
in selection as a parent is given to  phrases which have high scores 
within this rasa.  Often the new candidates would be similar to the 
parents and a particular rasa feeling would be perpetuated; other 
times, the offspring would not be considered by the players to 
convey the same emotional contour, and they would assign it to a 
different rasa class. 
In this way the music would wander between 
rasa classes,but often with shading of mood in between:
the new phrase may more perfectly express a different mood than 
the previous one,  its parents were selected by their fitness in that 
previous mood, and the offspring do come to share something of 
their qualities, even if they predominantly express a different mood. 
During the course of the performance, these relationships became 
more pronounced, as the overall population of phrases available are 
born of a longer process of selection, and come to represent more 
accurately the assessments of the performers.