Guess Scale or Chord from Notes

The music theory encoded in OMusic allows for some interesting applications. For example, omusic.guesser.guess takes a set of notes, then guesses which scale of chords the notes may be from.

import random
random.seed(44313)
from omusic.guesser import guess, tabulate_guess
from omusic.guesser import TEST_SCALES, TEST_SCALES_STANDARD

Note that guess takes two arguments: (a) a set of note names and (b) scales and chords to test against.

The module comes with several options for the latter:

Option	Included
TEST_SCALES_STANDARD	Major and minor
TEST_SCALES_MINORS	Natural, harmonic, and melodic minors
TEST_SCALES_EXPANDED	Augmented, diminished, pentatonic, and blues
TEST_SCALES_EXPANDED	Augmented, diminished, pentatonic, and blues
TEST_SCALES_MODES	From Ionian to Locrian
TEST_CHORDS	The (1, 3, 5) triad and sevenths
TEST_SCALES	Every scale. Probably has perfect matches for everything.

Try not to use scales and TEST_CHORDS together: because scales are larger, the default sorting criteria will prioritise them. Consider using sort_key=matched_percent instead.

Suppose we are transcribe a song with “G”, “E”, and “C#”. Call guess, then tabulate the result:

tabulate_guess(guess({"G", "E", "C#"},
                     TEST_SCALES)[:10],
               tablefmt="html")

Base	Mode	Matched	Unused	Unmatched
C	diminished, half whole	{'C#', 'G', 'E'}	{'A#', 'D#', 'F#', 'C', 'A'}	set()
C#	diminished, whole half	{'C#', 'G', 'E'}	{'A#', 'D#', 'F#', 'C', 'A'}	set()
C#	diminished, half whole	{'C#', 'G', 'E'}	{'A#', 'B', 'D', 'F', 'G#'}	set()
C#	blues minor	{'C#', 'G', 'E'}	{'G#', 'B', 'F#'}	set()
C#	locrian	{'C#', 'G', 'E'}	{'D', 'A', 'B', 'F#'}	set()
D	major	{'C#', 'G', 'E'}	{'D', 'A', 'B', 'F#'}	set()
D	harmonic minor	{'C#', 'G', 'E'}	{'D', 'A', 'F', 'A#'}	set()
D	melodic minor	{'C#', 'G', 'E'}	{'D', 'A', 'F', 'B'}	set()
D	diminished, whole half	{'C#', 'G', 'E'}	{'A#', 'B', 'D', 'F', 'G#'}	set()
D	ionian	{'C#', 'G', 'E'}	{'D', 'A', 'B', 'F#'}	set()

There are several good matches; half whole diminished C is unlikely to be the answer. Time to use your discretion: if the song sounds like a major, try to match for major and minor scales only:

tabulate_guess(guess({"G", "E", "C#"},
                     TEST_SCALES_STANDARD)[:10],
               tablefmt="html")

Base	Mode	Matched	Unused	Unmatched
D	major	{'C#', 'G', 'E'}	{'D', 'A', 'B', 'F#'}	set()
B	minor	{'C#', 'G', 'E'}	{'D', 'A', 'B', 'F#'}	set()
C	major	{'G', 'E'}	{'B', 'D', 'F', 'C', 'A'}	{'C#'}
C#	minor	{'C#', 'E'}	{'D#', 'B', 'F#', 'G#', 'A'}	{'G'}
D	minor	{'G', 'E'}	{'A#', 'D', 'F', 'C', 'A'}	{'C#'}
E	major	{'C#', 'E'}	{'D#', 'B', 'F#', 'G#', 'A'}	{'G'}
E	minor	{'G', 'E'}	{'B', 'F#', 'D', 'C', 'A'}	{'C#'}
F	major	{'G', 'E'}	{'A#', 'D', 'F', 'C', 'A'}	{'C#'}
F	minor	{'C#', 'G'}	{'A#', 'D#', 'F', 'C', 'G#'}	{'E'}
F#	minor	{'C#', 'E'}	{'B', 'F#', 'D', 'G#', 'A'}	{'G'}

Looks like D is the answer!