Although the mod7 system proposed here is meant to be used as a tool for the
analysis of post-tonal diatonic music, we need not limit ourselves to purely
diatonic music. That is, a mod7 analysis could still be a powerful tool when
applied to post-tonal music that is primarily diatonic, but that is embellished
with chromatic notes, provided that there is a sufficient musical reason to hear
the chromatic notes as embellishments. The mod7 system described here is
itself purely diatonic, and any pitch outside the prevailing diatonic collection in
a mod7 analysis will be understood as an alteration of one of its seven step-
classes. A mod7 analysis is therefore reductive to the same extent that the
music to which it is applied is chromatic. Two important decisions must be
faced in the mod7 analysis of music that is not purely diatonic: one must
determine what the prevailing diatonic collection is, and then determine how
the chromatic pitches embellish the diatonic ones.
To aid the analyst in determining the prevailing collections throughout a
musical work, this article proposes parsing the music into spans that contain at
least one complete diatonic collection (i.e. all seven pitch-classes of some
diatonic collection must be represented in any given span), beginning a new
span whenever a pitch-class appears that is not part of the current span's pitch-
class content, and closing a span once a complete diatonic collection has been
stated. For example, if the current span contains the DT±0 collection (the
notes of C major or one of its modes) and a B[ appears, then a new span is
begun. New spans should overlap as much as possible with the previous span;
i.e. they should be extended backwards up to a note with the same letter name
as the new pitch-class, but with a different accidental. For example, the new
span should be extended backwards in time from the B[ until a B occurs
(because B[ and B could not fit into the same diatonic collection). If the B[
mentioned above is preceded by an F major triad which is in turn preceded by
a G major triad, then the span should be extended backwards from the B[ to
include the F major triad, but not the G major one. In post-tonal diatonic
music, spans will often contain more than one diatonic collection because all
seven notes of any one collection will not appear before notes of another are
introduced. An example of such a span is found at the beginning of
Stravinsky's Serenade in A, given as Ex. 5. In this passage, both B[ and B
appear before either collection is completed, and thus fall under one span; all
seven notes of collection DT±11 are not played until bar 5, when E and G
appear for the first time, and the same holds true for collection DT±0.
The analyst should create a fuzzy set for each span with more than one
collection present indicating the degree to which the notes in the span belong
to each collection represented therein. Each fuzzy set would therefore consist
of two or more diatonic collections, each one with a value that indicates the
given span's degree of membership within that collection. For example, a fuzzy
set for the first six bars of Serenade in A would read {(DT±11, .97), (DT±0,
.90)}, and would indicate that 97% of the notes in the span suggest collection
DT±11 (the key signature of F major or D minor), while 90% of the notes in
the span suggest collection DT±0 (the key signature of C major or A minor).
These membership values are determined by dividing the number of notes in
the span that are part of the given diatonic collection by the total number of
notes in the span. In the case of Serenade in A, there are 124 notes in the span
(counting notes tied over the barline, but not counting notes tied within a bar),
Although the mod7 system proposed here is meant to be used as a tool for theanalysis of post-tonal diatonic music, we need not limit ourselves to purelydiatonic music. That is, a mod7 analysis could still be a powerful tool whenapplied to post-tonal music that is primarily diatonic, but that is embellishedwith chromatic notes, provided that there is a sufficient musical reason to hearthe chromatic notes as embellishments. The mod7 system described here isitself purely diatonic, and any pitch outside the prevailing diatonic collection ina mod7 analysis will be understood as an alteration of one of its seven step-classes. A mod7 analysis is therefore reductive to the same extent that themusic to which it is applied is chromatic. Two important decisions must befaced in the mod7 analysis of music that is not purely diatonic: one mustdetermine what the prevailing diatonic collection is, and then determine howthe chromatic pitches embellish the diatonic ones.To aid the analyst in determining the prevailing collections throughout amusical work, this article proposes parsing the music into spans that contain atleast one complete diatonic collection (i.e. all seven pitch-classes of somediatonic collection must be represented in any given span), beginning a newspan whenever a pitch-class appears that is not part of the current span's pitch-class content, and closing a span once a complete diatonic collection has beenstated. For example, if the current span contains the DT±0 collection (thenotes of C major or one of its modes) and a B[ appears, then a new span isbegun. New spans should overlap as much as possible with the previous span;i.e. they should be extended backwards up to a note with the same letter nameas the new pitch-class, but with a different accidental. For example, the newspan should be extended backwards in time from the B[ until a B occurs(because B[ and B could not fit into the same diatonic collection). If the B[mentioned above is preceded by an F major triad which is in turn preceded bya G major triad, then the span should be extended backwards from the B[ toinclude the F major triad, but not the G major one. In post-tonal diatonicmusic, spans will often contain more than one diatonic collection because allseven notes of any one collection will not appear before notes of another areintroduced. An example of such a span is found at the beginning ofStravinsky's Serenade in A, given as Ex. 5. In this passage, both B[ and Bappear before either collection is completed, and thus fall under one span; allseven notes of collection DT±11 are not played until bar 5, when E and Gappear for the first time, and the same holds true for collection DT±0.The analyst should create a fuzzy set for each span with more than onecollection present indicating the degree to which the notes in the span belongto each collection represented therein. Each fuzzy set would therefore consistof two or more diatonic collections, each one with a value that indicates thegiven span's degree of membership within that collection. For example, a fuzzyset for the first six bars of Serenade in A would read {(DT±11, .97), (DT±0,.90)}, and would indicate that 97% of the notes in the span suggest collectionDT±11 (the key signature of F major or D minor), while 90% of the notes inthe span suggest collection DT±0 (the key signature of C major or A minor).These membership values are determined by dividing the number of notes inthe span that are part of the given diatonic collection by the total number ofnotes in the span. In the case of Serenade in A, there are 124 notes in the span(counting notes tied over the barline, but not counting notes tied within a bar),
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