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"Mutation" is a piece for classical guitar and a multimedia system consisting of two Macintosh G4 computers. One of them, using Max/MSP, generates electronic sound in response to musical input. The other, using DIPS, generates animated images in real-time. These two are connected via Ethernet. The former sends cues and result of sound analysis to the other. Then, the latter channels the data so that they are used graphic parameters. In other words, the generated images are synchronized with the sounds.The piece has ten sections, A to I. The guitar begins section A with harmonics, which are prime series of notes and appear in most section of the piece. At the same time, A Max patch starts digitizing fragments of guitar sounds, employing granular synthesis techniques and immediately generating electronic sounds. Five granular engines in the patch generate at most five voices simultaneously.In section D, the guitar sounds are processed by comb filters and pitch shifters. Since the processed sounds respond to the ones with slight delay, they sound like a dialog between the guitar and the computer. The sound gradually becomes more tense and louder towards the next section.At the beginning of section E, the “granular arpeggiator”, developed by the composer, is employed for the first time to process guitar sound. It extracts grains out of guitar sounds and arpeggiates them.It combines two sets of more than ten tables, tempo and pitch tables, in different ways to alter the tempi and the pitches of arpeggios. In most cases when a table, stored in the patch in advance, is recalled one by one, the arpeggios are altered not immediately but gradually.In section E and F, several DSP techniques such as ring modulation, filtering, cross synthesis and flanger are employed to process the sounds of the guitar and the arpeggiator.Section G is a recapitulation of section A. section H, in contrast to the previous section consisting of harmonics, is the most intensive section of the piece. It begins with loud chords in a rush played with rasqeado of the guitar. After variations of motives. Several guitar phrases ascend towards the highest Ab, the goal note, and the last one finally reaches the Ab, which is retained in the opening of section I. This section is a long interlude by the arpeggiator.Section J, the coda, is a recapitulation of section D. This time, however electronic sounds do not follow the guitar. The coda is played only by the guitar.For the graphics, projected to the screen behind the guitarist, the particle effects and the environmental texture effects are mainly employed. Both captured images by digital video camera in front of the player and images of movie files, generated by an SGI computer are assigned as textures of three dimensional models of various kinds.
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