Creative Music Neurotechnology with Symphony of Minds Listening - Guide to Brain-Computer Music Interfacing - page 284

12.7.3.3 Pitch Delta Algorithm
Pitch delta represents the rate of change in the pitch values in each measure. The
algorithm works by calculating the difference between the initial pitch and the
successive pitch in each pair of notes. The pitch delta value is then used to trans-
form the input pitch by summing the two values together (Eq. 12.4 ).

New pitch ¼ successive pitch initial pitch f ð Þ þ initial pitch g ð 12 : 4 Þ

Assuming the same input as for the previous examples (Fig. 12.14 ), with a string
of note pitch values equal to {71, 71, 74, 72, 71}, the delta values for this trans-
formation are calculated as follows:

1. Delta 1 ¼ 71 71 f ð Þ 71 g

Delta 1 ¼ 0
New pitch 1 ¼ 71 no change ð Þ

2.

Delta 2 ¼ 71 71 f ð Þ 71 g

Delta 2 ¼ 0
New pitch 2 ¼ 71 no change ð Þ

3.

Delta 3 ¼ 74 71 f ð Þ 74 g

Delta 3 ¼ 3
New pitch 3 ¼ 77

4. Delta 4 ¼ 74 72 f ð Þ 74 g

Delta 4 ¼ 2
New pitch 4 ¼ 76

5. Delta 5 ¼ 72 71 f ð Þ 72 g

Delta 5 ¼ 1
New pitch 4 ¼ 73

The transformed output would therefore comprise a pitch string of {71, 71, 77,
76, 73}, which is rendered as {B4, B4, F5, E5, C#5}, as shown in Fig. 12.19 . Thus,
the application of the pitch delta algorithm gives the effect of exaggerating the
melodic intervals from a given measure; large intervals become even larger, while
melodies with little or no interval between successive notes remain unchanged.

Fig. 12.19 Transformed output created by the pitch delta algorithm