Robotics Reference
In-Depth Information
Rule-Based Music Systems
A month or so after the publication of Pinkerton's article, but clearly
inspired more by Mozart's dice game and similar methods, two American
mathematicians, Martin Klein and Douglas Bolitho, devised a program
running on a Datatron computer that composed music. Their program
used random decisions combined with a simple set of rules devised from
an analysis of hit songs that had reached the U.S.A. “top ten”. Klein and
Bolitho discovered a surprising similarity between the musical patterns
ofthesetoptensongs,andobservedthatthesimilaritywas“...sogreat,
that it sounds as if the same piece of music had been written over and
over.” [8] They distilled these similarities into three rules:
1. There are between 35 and 60 different notes in a popular song.
2. A popular song has the following pattern: part A, which runs eight
measures
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and contains about 18 to 25 notes, part A repeated,
part B, which contains between 17 and 35 notes; part A, again
repeated.
3. If five notes move successively in an upward direction, the sixth
note is downward and vice versa.
These first three rules were augmented by three more, set down by Mozart
and designed to assist in the writing of melodies:
4. Never skip more than six notes between successive notes.
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5. The first note in part A is ordinarily not the second, fourth or
flatted fifth note in a scale.
6. Notes with flats are followed by the note one tone down, notes
with sharps are followed by the note one tone up.
The Datatron computer's musical education consisted entirely of these
rules. In order to generate music the program would select a note at ran-
dom, verify that the note conformed to all of the rules (discarding any
notes that did not and generating new attempts in their place), and then
generate the next note. Despite its simplicity the program was able to
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A measure in music is a unit having a given number of beats. Measures are separated on the
staff by vertical lines called bars, and the term “bar” has become synonymous with measure.
22
Here, when Mozart says “skip” he means to include the current note as the first one skipped.
