After the model of the GimmeDaBlues style-sheet, a new format was needed in or- der to take advantage of the new features in PocketBand. A distinction was made be- tween the style data and the song data. The new “Song Style-Sheet” holds the data that is specific to each song, while the new “Style-Sheet” contains the information rela- tive to the voicing style.
Song Definition
The global attributes are situated in the “SONG DEFINITION” section in the begin- ning of the style-sheet and include the following items:
// SONG DEFINITION song title key signature bpm swing style sections
Table 6 Song definition area of the song style-sheet.
The name of the song is defined in the “song title” field and has to be written be- tween brackets. The “key” field is used to specify the root key of the song, which will be necessary for transposition purposes. The “signature” defines the time signature of the song, and is written as [beats * units]. A four by four signature is written as “4 * 4”. The “bpm” (beats per minute) is an integer value. “Swing” sets the swing level, ranging from 0 to 5, where a value of 0 will introduce no swing at all, and a value of 2 will produce 8th
triplets (see section
The “style” field specifies a template for voicings styles. The voicing is the set of notes or chord degrees that a given chord or scale definition will include. See below for more details.
The “sections” defines the number of sections the song will include. The number of section buttons available in the main sequencer interface will correspond to the number of sections defined in this field.
Section Definition
Following the song definition, there is a “SECTION DEFINITION” area for every sec- tion of the song. The section number and name are defined respectively in the “section” and “name” fields. The name of the section can be useful to help navigate and select the sections, which can include informative names like “Intro”, “Solos”, “Ending”, or any other desired text.
The number of bars in the section is defined in the “bars” field. The bars will have the number of beats defined in the “signature” setting. If no signature is defined in this section, the parser will use the bars defined in the “Song Definition” section. The same happens for the “bpm” setting.
// SECTION DEFINITION section name bars // signature // bpm // swing
Harmonic contents
The section definition area also defines its harmonic contents. After the “chords” keyword, the section’s chords are defined in the bar and beat where each chord will occur, followed by the chord root, chord type, scale type and duration. The example below specifies the chord sequence of a typical 12-bar blues form:
Fig. 47 A typical 12-bar blues chord progression.
The above blues form would be described in a style sheet as an indexed event list:
chords 1.1 C 7 mixo 1 2.1 F 7 mixo 1 3.1 C 7 mixo 1 4.1 C 7 mixo 1 5.1 F 7 mixo 1 6.1 F 7 mixo 1 7.1 C 7 mixo 1 8.1 A 7 mixo 1 9.1 D m7 minor 1 10.1 G 7 mixo 1 Db 7 mixo 1
11.1 C 7 mixo 0.2
11.3 A 7 mixo 0.2 Eb 7 mixo 0.2 12.1 D m7 minor 0.2 Ab 7 mixo 0.2 12.3 G 7 mixo 0.2 Db 7 mixo 0.2
Table 8 harmony definition for a 12-bar blues form in the section definition area of a song style-sheet.
The first element of each line represents the Bar and Beat at which the chord oc- curs. The number on the left of the “.” is the bar while the number on the right is the beat. “1.1” represents the first beat of the first bar. 11.3, for example, specifies the third beat of the eleventh bar. The following two elements are the Fundamental Note of the chord and the Chord Type. Chord fundamental is represented in the common A to G naming system. The type of chord notation is planned in order to keep it as similar to traditional jazz notation as possible. Chord types are defined in the “style-sheet” (see below). The next item is the Scale Type, which is also defined in the style-sheet. The scale type is use by the solo as well as the keyboard instrument algorithms. In the ex- ample above, mixo refers to an adaptation of the mixolidian mode. The last element, the Duration, is the length of the chord, defined in bars and beats. A “1” states a dura- tion of one bar, while a “0.2” for example states a duration of two beats.
Harmonic variations
A part of the standard improvisational procedures in jazz playing occurs at a har- monic level. The jazz musician learns to create harmonic variations by altering the chords of the song on the fly. Some of the possibilities or strategies for harmonic varia- tion include chord substitution rules by Steedman, 1984 (see section 4.2). The Pocket
Band Sequencer implements a simple mechanism to allow for harmonic variations, by allowing the user to define alternative chords for any chord entry. The alternative chords are defined after the first one, and use exactly the same syntax.
11.1 C 7 mixo 0.2
11.3 A 7 mixo 0.2 Eb 7 mixo 0.2 12.1 D m7 minor 0.2 Ab 7 mixo 0.2 12.3 G 7 mixo 0.2 Db 7 mixo 0.2
Table 9 Alternative harmony settings
The chords defined in Table 9 show three lines with alternative harmonies, in lines 11.3, 12.1 and 12.3, which are defined as an extra set of chord, scale and durations. This corresponds to a second layer of harmonic possibilities that can be used to create different harmonic trajectories. The sequencer then allows the user to introduce har- monic variations by changing the layer control in the harmony window. Using different layers will produce distinct variations as harmonic paths. As with the first path, the al- ternate chords data will be sent to the several instruments.
Fig. 48 Chord substitution example in the last two bars of a blues structure.
C 7 A 7 D m7 G 7 C
Eb 7 Ab 7 Db 7
In the example above, using the chord definitions in Table 9 of the last two bars of a blues 12-bar structure, we can see the several possibilities by moving arbitrarily be- tween the two chord layers.
A future development of this system could include a probabilistic algorithm for har- monic variation, using, for example, Chemilier’s implementation of Steedman’s chord substitution rules.