Music composed by computers has always been lacking in “musical” qualities:
mood, emotional expression and a sense of purposefulness or goal. A musical
expert system, called EMOTER, is the first attempt to address these important
musical aspects. EMOTER receives as input a list of moods (e.g., happy, lively)
and generates melodic passages intended to evoke those moods in an organized,
coherent fashion. EMOTER composes the basic units of music called phrases.
The program uses the mood-specification from a theory due to Deryck Cooke
to derive a few motifs (very primitive melodic material) exemplifying the moods
and computes a number of musical attributes to guide its compositional choices. A
theory of emotion due to Leonard Meyer further helps plan the phrase. The theory
states that an emotional response is stimulated in a listener when expectations
about the progression of the music are hrst established and then inhibited (with
the understanding that the expectations will eventually be fulfilled). A melodic
passage is composed using the selected motifs, attributes and emotional theory to create a “skeletal” phrase. This is embellished and developed (also using the
attributes and theory) to flesh—out the bare melodic material into a passage that
embodies the musical characteristics of the mood-specification.
Results with EMOTER are excellent. Many musical phrases comparable to
music of normal composers are generated from a single mood—specification. More
theory is needed, however, before the full complexities of human-composed music
are sufficiently captured in code for EMOTER to pass a Turing test in music composition.
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