Progressions

A Progression is a sequence of chords, each with a duration, played at a tempo.

Create a progression

Pass Chord objects, or lists of MIDI numbers or note names that become chords.

from chord_progressions import Chord, Progression

progression = Progression(
    [[48, 64, 67], [53, 69, 72], [55, 59, 62, 65], [48, 64, 67, 72]],
    durations=["2n", "2n", "1m", "1m"],
    bpm=100,
    name="I IV V7 I",
)

Progression([Chord(["C4", "E4", "G4"]), Chord(["D4", "F4", "A4"])])

Argument	Default	Meaning
`chords`	`[]`	the chords
`durations`	a whole bar (`"1m"`) per chord	one duration per chord, see below
`bpm`	`120`	tempo in beats per minute; a beat is a quarter note
`name`	`""`	a name for the progression

Durations

Durations use Tone.js time notation. These are supported:

Duration	Length	Beats
`"8n"`	eighth note	0.5
`"4n"`	quarter note	1
`"4n."`	dotted quarter	1.5
`"2n"`	half note	2
`"2n."`	dotted half	3
`"1m"`	one 4/4 bar	4
`"2m"`	two 4/4 bars	8

They are available as DURATIONS, and their lengths in beats as DURATION_BEAT_MAPPING.

Durations can also be given in seconds; each is rounded to the closest supported duration at the progression's tempo.

Progression([[60, 64, 67], [62, 65, 69]], durations=[1.2, 0.6], bpm=100).durations
# ['2n', '4n']

To convert yourself:

from chord_progressions.progression import (
    DURATION_BEAT_MAPPING,
    duration_to_seconds,
    seconds_to_duration,
)

duration_to_seconds("2n", bpm=100)  # 1.2
seconds_to_duration(1.2, bpm=100)   # '2n'

Read a progression

A progression behaves like a list of its chords.

len(progression)                    # 4
progression[0].notes                # ['C3', 'E4', 'G4']
[chord.type for chord in progression]
progression.durations               # ['2n', '2n', '1m', '1m']
progression.bpm                     # 100
progression.get_durations_in_seconds()
# [1.2, 1.2, 2.4, 2.4]

Key

key estimates the major or minor key that best fits the progression, with longer chords counting for more.

progression.key
# 'C major'

It raises a ValueError when no key fits, as when every pitch class sounds for the same length of time.

Method: Krumhansl–Schmuckler key finding, from Krumhansl, Cognitive Foundations of Musical Pitch, as implemented by music21.

Export a progression

progression.to_midi("progression.mid")   # one track at the progression's tempo
progression.to_audio("progression.wav")  # synthesized with 4 overtones per note; n_overtones=… to change
progression.to_json()
# [{'id': '…', 'ix': 0, 'duration': '2n', 'type': 'major chord', 'typeId': 63,
#   'notes': ['C3', 'E4', 'G4'], 'midi_nums': [48, 64, 67], 'metrics': {…}},
#  …]

Without a path, to_midi() returns a mido.MidiFile and to_audio() returns the samples as a NumPy array at 44.1 kHz. to_json() returns one entry per chord, with its position (ix) and duration.