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In-Depth Information
Table 12.5
MusEng
'
s memory after being trained with the musical sequence shown in Fig.
12.5
dir
int
dur
ω
FT1
0,
−
1, +1,
−
1
0, 5, 2, 4
120, 120, 120, 120
0.2
FT2
0, +1, +1,
1,
1
0, 1, 1, 1, 1
60, 60, 120, 60, 60
−
−
0.4
FT3
0, +1, 0
0, 1, 0
120, 120, 240
0.4
importance depending on how often the system is exposed to them. Notice,
therefore that FT2 and FT3 have higher
values than that of FT1, because they
ω
appeared twice.
12.7.2 Generative Phase
At the generative phase, MusEng generates new FTs by mutating the musicodes of
an existing FT towards those of another FT in memory. This process is in
uenced
by the values of
: FTs with larger
values are selected more often than FTs with
ω
ω
smaller
. This is because MusEng
uses a Gaussian distribution function to make this selection.
The very
values. Note that we wrote
'
tend to be selected
'
ω
first measure of a newly generated structure is typically informed by
the
first FT in memory (FT1). Let us consider this as the source FT for the mutation.
A second FT, the target FT, is selected from memory according to the values held in
memory for the variable
ω
, as mentioned above, and FTs with higher
ω
values tend
to be selected as targets more often than FTs with lower
values.
The generative process is illustrated below by means of a simple example using
the memory from the previous learning phase, but considering a mutation on a
single musicode only: melodic direction (dir). Therefore, let us assume the memory
scenario shown in Table
12.6
.
In order to generate a new measure, the dir musicode of the source FT1 will be
mutated towards the respective musicode values of a target FT. In this case, both
FT2 and FT3 have the same
ω
so there is an equal chance of FT2 or FT3 being
selected as the target FT, and a smaller chance of FT1. Let us assume that FT2 is
selected as the target. Thus, FT2
ω
'
is dir musicode is applied to FT1
'
is dir musicode to
produce a mutation (represented in bold) as follows:
f
0
; þ
1
; þ
1
;
1
;
1
g þ
0
;
1
; þ
1
;
1
f
g
¼ 0
;
0
; þ
1
;
1
;
1
f
g:
Note that the dir musicode has outlying maximum and minimum values of +1
and
1; hence, only the second value is actually mutated (+1) + (
1) = 0. Therefore,
−
−
the newly generated FT contains a dir musicode of {0, 0, +1,
1,
1}.
−
−
Table 12.6
A memory scenario with three FTs
FT1
FT2
FT3
dir
0,
1, +1,
1
0, +1, +1,
1,
1
0, +1, 0
−
−
−
−
0.2
0.4
0.4
ω
