Image Processing Reference
In-Depth Information
1 Introduction
The four-part classifier (FPC) system began as an experiment in randomly generating four-
part music that would abide by traditional four-part writing rules. The essential rules were
quickly coded along with the beginnings of a program for producing valid chord sequences.
But as the program evolved, it was moved in a new direction
—
one that could reuse the rules
already writen. The idea of creating a classiication system which could be trained with music
by known composers and tested with other music by the same composers became the driving
force behind the development of this tool.
1.1 Related Work
While computer classification of music is nothing new, research is lacking in the domain of
classifying
four
-
part
music. As for four-part-specific music systems, the 1986 CHORAL system
created by Ebcioglu [
1
] comes closest to FPC's precursor program geared toward composition.
Ebcioglu's system harmonizes four-part chorales in the style of J.S. Bach via first-order predic-
ate calculus. Newer research by Nichols et al. [
2
] most closely matches the mature version of
FPC but is not four-part specific. Like FPC, their system operates in high-dimensional space
(FPC was developed in 19-space and later expanded to 22-space) but parameterizes the music-
al chord
sequences
of
popular
music. FPC does not consider the order of chords in its analysis
but focuses instead on chord structure and the movements between parts.
1.2 Explanation of Musical Terms
In order for FPC to be understood in the steps that follow, a basic level of musical knowledge
is required.
There are 12 pitches in a chromatic scale from which are derived 12 major keys. The names
of each key range from A to G and include some intermediate steps between leters such as Bb
or F#. Most importantly, the key serves as a musical “anchor” for the ear. All pitches can be
understood in relation to the syllable
do
(pronounced “doh”), and all chords in relation to the
I chord (the tonic). Both
do
and the I chord are defined by the key.
Although each key contains 12 pitches (or steps), only 7 of them make up the diatonic scale
(
Figure 1
)
—
the scale used most often in western music (
do
,
re
,
mi
,
fa
,
sol
,
la
,
ti
,
do
). From bottom
to top, the distances between the notes of the diatonic scale follow the patern “whole step,
whole step, half step, whole step, whole step, whole step, half step.” Whether traversing the
diatonic scale requires multiple sharps or flats is determined by the key signature at the begin-
ning of the piece.
FIGURE 1
Diatonic scale in C.
From these seven diatonic notes, seven diatonic chords are possible. In four-part music,
each chord is made up of four voices: soprano, alto, tenor, and bass. The arrangement of these
voices produces chords in specific positions and inversions. For the sake of simplicity, the ex-
act procedure for determining chord names and numbers has been omited.
Notes differ not only by pitch but by duration. The shortest duration FPC handles is the
eighth note followed by the quarter note, the doted quarter note, the half note, the doted half
note, and lastly the whole note. The time signature dictates the number of beats in a measure
and what type of note constitutes one beat. For example, in 3/4 time, there are three beats in
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