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Darwin Day PACMF09 Preview Event : Music Notes

As part of the run-up to PACMF09 ( on Thurs 12th Feb there were four Darwin 200 celebration events of music, performance, talks, film and a party at 12pm, 6pm, 7pm and 7:20pm in the Roland Levinsky building at the University of Plymouth. All events were free. Dance performances were given by Adam Benjamin and performance students, and visuals were provided by James Eden and Olly rooks. Alexis Kirke composed two pieces of Music: "Happy Birthday to Darwin" and "Evolution of the Visual Cortex". This document describes the composing of the two pieces.

"Happy Birthday to Darwin"

The aim of "Happy Birthday to Darwin" was to use Darwin-inspired techniques to generate base-material for a 20 minute piece of ambient music. An artificial society of 2048 creatures was created (called "Celebroids"). The measure of a Celebroid's sexual attractiveness was how well it could sing a monophone tune of "Happy Birthday". A Celebroid's performance of Happy Birthday was encoded in its genes using a direct MIDI encoding. A gene gives a certain position in a 30-dimensional Happy Birthday space (15 dimensions for note onset time, 15 dimensions for pitch). At the origin of the space is the correct Happy Birthday - the closer an agents MIDI file/gene is to the real happy birthday (based on Cartesian distance), the more sexually attractive the Celebroid is considered. Celebroids are single-sexed and can all breed with each other, however in each generation only the top 20% "sexiest" Celebroids will breed (i.e. the ones who are best at singing Happy Birthday). The evolution of Celebroids is shown below in a graph - the measured "fitness" of the most sexually attractive Celebroid in each geneartion is plotted - 400 generations were run for this composition.

The offspring of two Celebroids will consist of a random combination of part of the two parents' genes (i.e. MIDI tunes), together with a 15% mutation rate - i.e. there is a 15% chance of a part of a gene being mutated. These processes of Crossover and Mutation are analogs of Darwinian evolution.

The composition was constructed by taking the MIDI files of the sexiest 4 Celebroids, and the 4 most ugly Celebroids at semi-regular intervals. These were put into the music software Propellorhead Reason and assigned timbres (some pitched and some non-pitched), and a performance was constructed using parameter tracks in Reason. The aim of the composition was to provide a coherent ambient aesthetic progression, but also to showcase occasionally the progression of the Celebroids evolution at singing Happy Birthday. Part of the piece in Reason is shown below.


The result ambient composition can be heard in MP3 format here: Happy Birthday to Darwin.


"Evolution of Visual Cortex"

During the performance of Happy Birthday to Darwin, Adam Benjamin and his students were moving around the space through constructions set up by James Eden and Olly Rooks. The movement caused pens in the constructions to draw shapes which represented various aspects of the dancers' movements. Two pictures were constructed, and James and Olly then scanned the pictures in computer bitmaps, split them into 20 files which were sent to composer Alexis Kirke. Examples of the pictures are shown below.

The main elements of the pictures were black and white lines, often crossing over each other. Alexis constructed a very simple visual cortex in the computer modelling software which would take as input a bitmap and "react emotionally" to it. It has been found in previous research that some groups of cells in the visual cortex in the human brain respond to certain fixed visual elements. For example: to vertical lines, or moving horizontal lines etc. Alexis' system reponds to two visual elements: firstly the density of the picture (i.e. how much drawing there is on it, and how much white space); secondly to how many crossing lines there are. To convert these into emotions he uses the Arousal/Valence model of emotions. Valence is how positive or negative an emotion is - for example Happy is high Valence, Sad is low Valence, suicidal is even lower Valence. Arousal is how intense an emotion is. For exampe Anger and Sad are both negative valence, but Anger has higher arousal than sadness. Also Tender and Happy are both high valence, but Happy has high Arousal than Tender. The emotional space is shown below.











The basic rule of Alexis' system is that the density of black lines affects arousal, and the number of crossing lines affects valence. For example a large number of crossed-over lines will lead to a lower valence (less positive emotion), but parallel lines will lead to a high valence (more positive emotion). Similarly if there are a lot of lines on the paper it will lead to a higher arousal, whereas an almost blank sheet will lead to a low arousal. The logic of this is that violent scribbling seems more negative compared to calm parallel lines - and that the more dense the scribbling, the more intense the emotion. Alexis and the artists compared the artificial visual cortex's estimated emotions to how they personally responded to some previous pictures, and were satisfied enough with the match to utilize the cortex a piece of music.

This information was combined with Alexis' algorithmic composition and performance system PERCOM. Originaly PERCOM was designed to take as input EEG Brain waves and compose and perform a new piece of music to express the emotions detected in the brain waves. For this project, Alexis replaced the EEG with his simple specialised visual cortex model. So the combined system will be able to look at a picture, and then generate music to express the emotion in the picture. The resulting emotions detected by PERCOM in the pictures produced during the lunchtime performance are shown below and are: tender, happy, happy, tender, happy, angry, tender, happy, tender, tender, happy, tender, tender, happy, angry, angry.


As base material for the composition, Alexis recorded improvisor Sam Richards playing 29 short themes. These were converted into monophonic MIDI files and then used as the "building blocks" for the PERCOM performance composition. PERCOM combined these blocks into a its own structure in its own order, applying pitch, timing and loudness transformations based on desired emotional effect. This composition was then loaded in Propellorhead Reason and swing quantized, human-type errors were added, and two other timbres were use to occasionally accompany the piano. The process (going from receiving the pictures to producing the final composition) had to be done in less than 3 hours, due to the first performance finishing at 2pm, and the second performance coming at 6pm.

The resulting composition can be heard here: Evolution of Visual Cortex. (In the final performance, Sam Richards improvised along with the composition, however this MP3 does not include that.)


More of Alexis Kirke's work can be heard at Interface II during the PACMF09 festival ( on 28th February 2009 at 9pm.


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