Researchers developed two prototypes of their automatic disc jockey system (hpDJ), both of which use genetic algorithms (GA) to create song mixes. Inspired by Darwin's theory of evolution, genetic algorithms encourage the best solutions generated and throw away the worst ones ("only the fittest survive") so that the population keeps improving as a whole.
Each solution is encoded into a string called DNA. Researchers then asked listeners to rate each sound sample and then assigned each a "fitness" function based on these ratings. Only the fittest samples were selected to create the next generation -- in this case, the next sound sample.
The first prototype, GA (genetic algorithm) Drum machine, is a simulation of a marching band where the patterns of each instrument (snare drum, bass drum) are encoded into a fragment of DNA, which can evolve and mutate.
The simulated marching band creates rhythms by taking inspiration from a recording of someone tapping on a table, humming or singing. This information is mixed with pre-defined rhythms.
The second prototype uses pre-recorded samples (loops) to create music. The music is encoded into a DNA that controls how the loops are organized to play together.
A human listener rates the result, and hpDJ uses this feedback to generate the next generation of songs. At the next generation, the best individuals (i.e. songs) are combined and mutated to create new songs. The next generation is presented to the user for ratings, and so on.