A
pitch class is a type of pitch name, such as C, C#
or D, regardless of octave range. Particular
pitch classes can be grouped together as a pitch
class set, for example; C, D, E, G, A. In music
theory these are more often referred to as an
ordered list, which are called scales, for example
the Pentatonic Scale. Some scales are called
modes, such as Aeolian or Phrygian mode. These
pitch sets are also related in some cases to the
key of the music, for example C Major.
While this might sound complicated (and it can get
so) all this can be looked up in various music
theory texts.
The most common use of the pitch class sets in
SoundCipher is to enable you to restrict note
pitches to a particular scale or mode. So you can,
for example, play music in A minor.
In code a pitch class set is described as an array
of floats with values in the octave from 0-11. For
example, float[] BLUES = {0, 3, 5, 6, 7, 10};
Check the documentation for a complete list of
pitch class sets.
The pitch class sets are Java constants, which
means they cannot be changed and also, by
convention, that their names are written in
UPPER case. They are automatically included in
ScoundCipher instances and so can be accessed by
de-referencing, for example; sc.MINOR;
Let's look at how they can be used. First in a
non-sounding example. The idea is to quantize a
pitch value so that it is one that is within a
nature minor scale.
After importing the SoundCipher library and
creating an instance of it called sc, a
variable pitch is set to a random value between 60
and 80. A boolean flag, inScale is
initiated as false, assuming that the random
choice may not be a member of a pitch class set
(not a scale degree).
The while loop checks the pitch against every
scale degree (number in the set) and if it is not
within the scale it makes a new random selection.
This process continues until a scale degree is
selected, then this pitch value is printed.
An important bit of math is the modulo function
(%) that reduces the pitch to its octave position
by returning the remainder when dividing by 12.
This results in a number between 0-11 and this is
compared to the numbers in the pitch class array
for the specified scale.
Minor Riff
Now let's look at applying this process in a
musical context. We'll create a short random riff
that is in a minor key (only using pitches from
the minor pitch class set).
The process of checking for inScale has been made
into the function called modeQuantize
(with a few refinements).
The random riff is written twice to a score (to
repeat it for some more musicality) then played. A
callback at the end of the riff causes the process
to be repeated.
The whole process is looped 8 times and the
graphics count this down visually.
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