Robotics Reference
In-Depth Information
EMI's pattern matcher is able to detect such patterns automatically,
although variations between several works by the same composer might
mean that it needs to find not only patterns that are exactly alike, but
also patterns that are almost the same. Humans are able to detect similar
musical ideas rather easily, but the task is considerably more difficult for
a computer program because rhythms, pitches, and the locations of pat-
terns within a measure can vary without changing the composer's basic
musical idea. EMI surmounts this problem by employing a method that
examines the
intervals
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between the pitches of successive notes, rather
than the actual pitches themselves. This method, converting the transi-
tions from one note to the next into a sequence of numbers, enables EMI
to recognize similar sequences of notes even though the actual pitches in
the sequences may be very different.
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When a signature pattern is de-
tected it is stored in the
signature dictionary
, a database that provides the
fragments to be used in the reconstruction stage.
Once it has prepared the functionally tagged lexicons of building
blocks and a signature-dictionary with patterns of different types, EMI
can use these to generate new music. This process, which is carried out
by EMI's reconstruction module, consists of composing musical phrases
in which building blocks are re-ordered using the same ordering logic
from their functional analysis, and inserting signatures in appropriate
places within a block. The success of
recombitant
music, as this is called,
depends on retaining the musical logic present in the original work. Mu-
sic follows progressions that our ears have learned to expect, with certain
sounds happening only at the beginning, middle and end of a phrase.
EMI analyses all the musical groupings from the pattern matching func-
tion to determine their role within these progressions. This involves de-
termining what harmonic pattern the groupings correspond to, so that
when the elements are mixed and matched they are placed in the right or-
der according to their function. This allows the piece to be put together
following musical “logic” rather than being randomly selected.
The system creates a musical phrase by choosing as its first bar one
that has been tagged as a “first bar” because it was the start of a musical
phrase in one of the original pieces of the composer's music. (This is
determined by the analysis module.) Then it chooses a next bar from all
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An interval is the distance between notes on a musical scale. EMI counts these distances in half
steps—the difference in pitch between adjacent keys on a piano.
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For example, two sequences might consist of identical notes in terms of whether they are A, B,
C, D, etc., but one octave apart. Although the pitches are completely different, the intervals are the
same.
