Evochord installation

Video and stereo audio generated in real time (2005).

Short note on the work

Evochord is an installation in which a genetic algorithm tries to evolve a harmonious chord. Sound and visual output are generated in real time. The visual output consists of coloured shapes, one for each note of the chord; red indicates low, green intermediate and blue high pitches. The pitches in the chord are not tied to any scale, but are freely variable.

The overall process is controlled by a variable mutation rate, which changes from high to low and back to high in a cycle lasting about one hour. The mutation rate is indicated visually by movement of the shapes on the screen. Each hour-long cycle is different, because of the random nature of the mutations.

Longer note on the work

Evochord is an installation in which a genetic algorithm tries to evolve a harmonious chord.

Sound and visual output are generated in real time on a computer. The visual output consists of coloured shapes, one for each note of the chord; red indicates low, green intermediate and blue high pitches. The pitches of the notes in the chord are not tied to any scale, but have a resolution of about 1/900 of a semitone (0.11 cents). At any time, what is seen and heard is the single most consonant chord of a population of 100 chords inside the computer. Consonance is measured according to a version of a formula from William Sethares.

Every four seconds a new generation of chords is created from the previous generation by first breeding pairs of chords and then mutating the progeny.

The overall progress of the algorithm is determined by the mutation rate, which varies from very high to very low and back again with a cycle time of about an hour. The mutation rate is indicated visually by movement of the shapes on the screen. At a high mutation rate the chord is continually changing violently; at lower mutation rates it can be stable for quite long periods, or subtle changes can occur. The stable chords are complex enough to repay extended listening.

Each cycle is different, because of the random nature of the mutations. The cycle is in fact not long enough for the best solution to be found; instead different “interesting” chords will evolve each time.

The installation is intended to be primarily an artistic experience and secondarily a partial visualisation and sonification of a genetic algorithm.

Images

Two images from the installation. Click on the small images below for enlarged versions.

High mutation rate

Low mutation rate

Video

Here is some video documentation of Evochord (duration 3'25"). It contains some samples from one cycle of the installation along with a brief explanation of the process. A higher-quality version is available on DVD from Gordon Monro.

Technical requirements

The piece is available as a Mac OS X executable.
The piece is intended to be projected via a video projector and a stereo sound system (PA) in a space with no competing sound. The speakers need to be of reasonable quality to enable the low notes in the chords to be heard.
It is intended that people would watch and listen for a little while, walk around and come back a little later to observe what has happened.
The short explanatory video could be made available via a TV or monitor and headphones as a supplement to the installation.

Further information

More explanation (PDF, 261 Kbytes)

Showings, etc.

I gave a presentation (PDF, 261 Kbytes) on this piece at the Generative Arts Practice 05 conference, University of Technology, Sydney, 6th December 2005.
Presented in the Street Cinema section of Project 3, part of the Adelaide Festival of Arts, on 15th and 16th March 2006.
Presented at the 2006 Australian Computer Music Conference, Elder Conservatorium, University of Adelaide, 11–13 July 2006.
Accepted for the 2006 Generative Arts Conference in Milan, Italy, 13-15 December 2006.

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