Chords

A Chord is a set of unique notes.

Create a chord

Give the notes as MIDI numbers or as note names. Duplicates are dropped and the notes are sorted from low to high.

from chord_progressions import Chord

Chord([60, 64, 67])
Chord(["C4", "E4", "G4"])

Chord([67, 60, 64, 60]).midi_nums
# [60, 64, 67]

MIDI numbers must be between 0 and 128.

Read a chord

chord = Chord([60, 64, 67])

chord.midi_nums  # [60, 64, 67]
chord.notes      # ['C4', 'E4', 'G4']
chord.type       # 'major chord'
chord.typeId     # 63
chord.template   # [1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0]
chord.id         # a random UUID, unless one is passed: Chord([60, 64, 67], id="tonic")

type is the chord's name in Vladimir Ladma's list of pitch-class sets; the names and their ids are covered in Notes and chord types. template marks which of the 12 pitch classes, starting at C, the chord contains.

metrics holds measures of the chord's notes:

chord.metrics
# {'num_notes': 3, 'num_pitches': 3, 'pc_cardinality': 3,
#  'interval_class_vector': [0, 0, 1, 1, 1, 0], 'ambitus': 7, 'evenness': 5.078...}

Key	Meaning
num_notes	number of notes
num_pitches	number of distinct notes
pc_cardinality	number of distinct pitch classes
interval_class_vector	count of each interval class, from minor second to tritone
ambitus	semitones between the lowest and highest note
evenness	how evenly the pitch classes divide the octave (Block and Douthett, 1994)

More measures are available as functions; see Measures.

Export a chord

chord.to_json()
# {'id': '…', 'midi_nums': [60, 64, 67], 'type': 'major chord', 'typeId': 63,
#  'notes': ['C4', 'E4', 'G4'], 'metrics': {…}}

chord.to_midi("chord.mid")   # one second of the chord at 120 bpm
chord.to_audio("chord.wav")  # one second of the chord, synthesized with 4 overtones per note

Without a path, to_midi() returns a mido.MidiFile and to_audio() returns the samples as a NumPy array at 44.1 kHz.