History of Electroacoustic Music
In 1977 Joel Chadabe purchased a special Synclavier system that allowed special software and performance interfaces to be added to it. In 1978, his piece Solo used the Synclavier system with a program Chadabe had written that composed melody notes based around predefined parameters of harmony and melody. Melodies were created for eight melody lines played by the Synclavier, two clarinets, two flutes, and four vibraphones. In performance, Chadabe controlled the composition with two modified theremins that were created by Robert Moog. The two theremin antennae were placed on the stage, about three feet apart. Moving a hand towards or away from one of them controlled the tempo by changing the durations of the notes. Moving a hand in the proximity of the other antenna controlled the relative volume of the instruments (thus, the overall timbre produced). Chadabe described performing the piece as being like "a conversation with a clever friend." He could do things like cue the clarinets to play slowly, but he did not know what notes the clarinets would play. The notes they produced determined his decision for the next note produced. In 1981, Chadabe coined the term interactive composition to refer to a process in which a performer shares control of the music with a computer.
Chadabe's piece Follow Me Softly (1984) was an improvisation with Chadabe on the Synclavier system and a percussionist. Chadabe sat at the alphanumeric keyboard and was able to control the triggering of notes, changing of timbres, or produce melodic figures.
While Chadabe was developing his pieces involving the Synclavier, Morton Subotnick had taken a step beyond the sequencing techniques featured on his early albums. His "ghost" box featured a pitch and envelope follower for live audio input. Once changes in pitch and amplitude were converted to voltage changes, these changes could be sent to an amplifier, a frequency shifter, and a ring modulator. The parameters of these processors could be controlled by moving a finger across a touch sensitive plate, thus "invisible" gestures could control the performance -- hence the name "ghost" box. These manual gestures could also be recorded onto tape and played back at each performance.
Subotnick worked with the "ghost" box until the mid-1980s. His pieces that used it include Two Life Histories (1977), Liquid Strata (1977), Parallel Lines (1978), The Wild Beasts (1978), The Last Dream of the Beast (1979), A Fluttering of Wings (1981) and Axolotl (1981).
Robert Rowe (1954-), who trained at the Institute of Sonology from 1978 to 1987, IRCAM, and received the first music Ph.D from the MIT Media Lab in 1991, has made a systematic study of interactive computer music systems. He considers such systems to be an intersection of the fields of music theory, music cognition, and artificial intelligence, and thus has taken Mathews' idea of the intelligent machine to new levels. His work examines how computers may be programmed to "sense" salient musical features such as individual phrases, tempo, density, loudness, register, and harmonic progression. Based on what computers "sense," they may then process incoming music and be programmed to "respond" to the input of a human musician. Thus, his work explores new ways in which computers may be made to interact with human musicians.
Rowe classifies interactive music systems according to interactions of three dimensions:
Rowe's own software program Cypher receives incoming music in the form of MIDI data, and outputs its responses in the form of MIDI data. A Listener analyzes six types of input features, plotting each MIDI event onto a six-dimensional feature space with axes representing speed, density, dynamic, register, harmony, and rhythm. These six feature streams are tracked over time for regularity or irregularity. A Player is configured by a composer to output certain features in response to certain input features. Working with a graphical user interface, a composer can specify instructions such as what timbres should be played, and for transformations such as, for example, extra accents to be added to the output material when the input material is being played in a low register, a pitch to be output that is an inversion about a note (such as Middle C) of the input pitch, or for regularity or irregularity of a certain feature affecting the phrase length of output material. A series of these connections are stored as "states" that advance throughout the course of a piece. A Critic tracks the Player's output. In the absence of input from a musician, the Critic has the Player continue to generate material based on features that the musician has recently played.