Western Notation

The WesternNotation class is an implementation of the American standard pitch notation (ASPN), which designates octaves by numbers with C4 being the “middle C” and a frequency centering of \(A4 = 440Hz\).

Note

This chapter only gives a brief overview of features specific to this notation. For a general overview on what you can do with the various musical objects in xenharmlib head to the Quickstart.

A WesternNotation context is created like this:

from xenharmlib import WesternNotation

n = WesternNotation()

Note objects are created as follows:

a4 = n.note('A', 4)
print(a4.frequency)

Frequency(440)

Intervals can be created by their Western shorthand name, with the first parameter being the interval quality (minor, Major, diminished, Augmented) and the second being the scale degree (1-indexed):

# augmented five
aug5 = n.shorthand_interval('A', 5)
print(aug5.cents)

800.0

# diminished fourth
dim4 = n.shorthand_interval('d', 4)
print(dim4.cents)

400.0

# major third
maj3 = n.shorthand_interval('M', 3)
print(maj3.cents)

400.0

# minor second
min2 = n.shorthand_interval('m', 2)
print(min2.cents)

100.0

Intervals in WesternNotation are “harmonic function aware”, meaning that transposition by enharmonically equal but functionally different intervals will result in enharmonically equal but functionally different notes:

C4 = n.note('C', 4)

note_a = C4.transpose(maj3)
note_b = C4.transpose(dim4)

print(note_a)
print(note_b)

WesternNote(E, 4)
WesternNote(Fb, 4)

print(note_a == note_b)

True

Intervals created by two notes (e.g. by calling the interval() method of a note) can be examined to obtain their shorthand name:

D4 = n.note('D', 4)
Fsharp4 = n.note('F#', 4)

interval = D4.interval(Fsharp4)

print(interval.shorthand_name)

('M', 3)

Other than with the scale() method scales in WesternNotation can be defined by only providing a list of pitch class symbols and an (optional) root base interval with the pc_scale() method:

C4maj = n.pc_scale(['C', 'D', 'E', 'F', 'G', 'A', 'B'], 4)
print(C4maj)

WesternNoteScale([C4, D4, E4, F4, G4, A4, B4])

WesternNotation implements a default enharmonic strategy, so transposition by integers is possible:

D4 = n.note('D', 4)
note = D4.transpose(1)
print(note)

WesternNote(D#4])