Period
notation
In
the same way it deals with superimposed sequences, the polymetric expansion
algorithm works out equal symbolic durations between beat separators notated
'•' -- the "period notation." A note sequence in period notation and the
context-free grammar it originated from (composed by Harm Visser) are shown
Fig.12. See "-gr.acceleratio
n"
in the VISSER & MONTAUDON folder.
In
this example, beats contain increasing numbers of notes resulting in an
accelerating movement. Velocity assignments have of course no effect on
durations.
S
-->
_vel(60)
A B _vel(65) C D _vel(70) E F _vel(75) G _vel(77) H _vel(80) I _vel(85) J
_vel(87) K _vel(90) L
A
--> E2 •
B
--> D2 A
C
--> B2 B
D
--> G2 C
E
--> F#2 D
F
--> A#2 E
G
--> C2 F
H
--> G#2 G
I
--> A2 H
J
--> D#2 I
K
--> C#2 J
L
--> F2 K
BP2
score:
Velocity
controls have been left out
E2
• D2 E2 • B2 D2 E2 • G2 B2 D2 E2 • F#2 G2 B2 D2 E2
• A#2 F#2 G2 B2 D2 E2 • C2 A#2 F#2 G2 B2 D2 E2 • G#2 C2 A#2
F#2 G2 B2 D2 E2 • A2 G#2 C2 A#2 F#2 G2 B2 D2 E2 • D#2 A2 G#2 C2 A#2
F#2 G2 B2 D2 E2 • C#2 D#2 A2 G#2 C2 A#2 F#2 G2 B2 D2 E2 • F2 C#2
D#2 A2 G#2 C2 A#2 F#2 G2 B2 D2 E2 •
Fig.
12: A grammar producing an accelerating sequence of notes, and the resulting
item in BP2 score notation
Once
the grammar has been typed, the user may select "Produce items" to get a text
or graphic display of its production, listen to it on the MIDI output, and
optionally produce a Csound score. The output of the "acceleration grammar" of
figure 2 is displayed on a piano-roll score:
Fig.13:
A piano-roll of the item produced by the grammar of Fig.12
