User’s Guide, Chapter 9: Chordify

Chordify is a madeup word that we created in music21 for the process of making chords out of non-chords. Chordify powerful tool for reducing a complex score with multiple parts to a succession of chords in one part that represent everything that is happening in the score. Take this short chorale by Bach:

from music21 import *

b = corpus.parse('bwv66.6')

Let’s take it and chordify it using the chordify() method.

bChords = b.chordify()

TA-DA! Every note in the score is now represented in a single chord and every moment where some element moves is also represented. Sometimes this process of chordifying is called “salami slicing,” that is, cutting the score so thinly that every moment where something happens is fully represented.

Now we can see if there are any (fully-notated) dominant seventh chords in the piece. The new chordified part still has measures, so we’ll flatten the chordified part first to get to the chords. It might also have time signatures, etc., so we will filter them out so we only have chords.

for thisChord in bChords.recurse().getElementsByClass('Chord'):
    if thisChord.isDominantSeventh():
        print(thisChord.measureNumber, thisChord.beatStr, thisChord)
 2 2 1/2 <music21.chord.Chord B4 G#4 D4 E3>
 3 2 1/2 <music21.chord.Chord G#4 E#4 B3 C#3>
 4 3 1/2 <music21.chord.Chord F#4 D#4 A3 B2>
 8 2 <music21.chord.Chord F#4 E4 C#4 A#2>

Sure enough we can check the score above and see that there are four of them: three of them on the offbeat (m.2 beat 2.5, m. 3 beat 2.5, and m. 4 beat 3.5) which are made from passing motion, and one of them in m. 8 beat 2 also in a metrically weak position.

We can see the chordified version by callling ”.show()” on bChords itself, but it’s probably better to see it in the context of the whole score. Let’s put it in the score at the beginning (all Part objects should go at the beginning) and then show just measures 0 (pickup) to 4:

b.insert(0, bChords)
b.measures(0, 4).show()

That’s a bit messy to read, so let’s put all these chords in closedPosition (see User’s Guide, Chapter 7: Chords for more information).

for c in bChords.recurse().getElementsByClass('Chord'):
    c.closedPosition(forceOctave=4, inPlace=True)


Note that when we move a chord to closed position, unfortunately it loses its tie information, since the pitch that starts a tie can’t tell whether or not the next pitch will end up in a different octave (for instance, the Cs in the first two notes of the second full measure). Maybe it’s something we can do someday...

We can use the function roman.romanNumeralFromChord to label each of the chordified Chords:

for c in bChords.recurse().getElementsByClass('Chord'):
    rn = roman.romanNumeralFromChord(c, key.Key('A'))

b.measures(0, 2).show()

We can also see everything directly if we look at the .show('text') output:

 {0.0} < 0 offset=0.0>
     {0.0} <music21.clef.TrebleClef>
     {0.0} <music21.key.KeySignature of 3 sharps, mode minor>
     {0.0} <music21.meter.TimeSignature 4/4>
     {0.0} <music21.chord.Chord A4 C#5 E5>
     {0.5} <music21.chord.Chord G#4 B4 E5>
 {1.0} < 1 offset=1.0>
     {0.0} <music21.chord.Chord F#4 A4 C#5>
     {1.0} <music21.chord.Chord G#4 B4 E5>
     {2.0} <music21.chord.Chord A4 C#5 E5>
     {3.0} <music21.chord.Chord G#4 B4 E5>
 {5.0} < 2 offset=5.0>
     {0.0} <music21.chord.Chord A4 C#5 E5>
     {0.5} <music21.chord.Chord C#4 E4 A4>
     {1.0} <music21.chord.Chord E4 G#4 B4>
     {1.5} <music21.chord.Chord E4 G#4 B4 D5>
     {2.0} <music21.chord.Chord A4 C#5 E5>
     {3.0} <music21.chord.Chord E#4 G#4 C#5>

We can also just extract the lyrics, where we stored the RomanNumeral information:

for c in bChords.measures(0,2).flat:
    if 'Chord' not in c.classes:
    print(c.lyric, end=' ')
 I V6 vi V6 I V6 I I6 V V7 I III6

More complex scores can also be chordified. If there are lots of tuplets, you might get odd results. Such as with Opus 19, no. 6, by Arnold Schoenberg.

schoenberg = corpus.parse('schoenberg/opus19', 6)

There are more specialized commands for .chordify, so if you want to learn more, look at the chordify() documentation. We will get to the option, addPartNameAsGroup later, which will let you know exactly where each pitch in the chordified Chord comes from. But for now, let’s jump to our first example, Chapter 10: Example 1