Robotics Reference
In-Depth Information
to a relatively unknown Bush health plan . Of about 2,500 women
polled, 49 percent said they'd rather date the president, while about
one-third of singles said they would prefer Democratic challenger
John Kerry.
How Computers Compose Music
The composition of music by computer has attracted the interest of
many researchers since the earliest days of AI, possibly because music
is the world's most popular art form. Computer music now has an ex-
tensive literature of its own, somewhat independent of the rest of the
AI community, including academic journals that focus on the subject.
With the advent of the personal computer, thousands of enthusiasts have
tried their hand at developing programs to compose music of one sort or
another.
The automated composition of music has its roots in several inven-
tions that used dice and other methods of chance to randomly select
the notes, bars and even the rhythms of a piece of music. Examples of
such techniques are the writings of Athanasius Kircher and Wolfgang
Amadeus Mozart described earlier.
17
Markov Chains in Music
Algorithmic methods of music composition have always been popular
with computer music enthusiasts, partly because they are relatively easy
to program. One such method is based on the use of Markov chains. In
the February 1956 issue of
Scientific American
, Richard Pinkerton pub-
lished an article on Markov chains, entitled “Information Theory and
Melody”, in which he described how a statistical analysis of nursery tunes
enabled him to create a system of melody, rhythm and harmony, itself ca-
pable of composing tunes in the same genre. His system modelled the
basic qualities of symmetry and regularity found in the melodies of the
tunes he used to set up his database.
Pinkerton selected 39 tunes from a children's song book and counted
the frequency with which each note appeared
18
—there are eight possible
notes altogether, including the rest (or pause). From the frequencies of
17
See the section “Creativity” in Chapter 2.
18
To simplify matters Pinkerton converted all the tunes to the key of C and he treated all the
notes as though they were in a single octave, so that middle C and the next C above it were both
counted simply as C.
