Music21 Basics

Learn more about music21, created by Dr. Myke Cuthbert, supported by MIT, and generously shared with the musicological community.

Music21 is used as part of CRIM Intervals to do all of the 'heavy lifting' to find notes, intervals, and so on.

This tutorial explains some of the key music21 methods used in CRIM Intervals.

Import the Libraries

from music21 import *
import music21 as m21
import requests
import pandas as pd
# !pip install musescore-scraper

Load and Convert MEI to a Music21 object

path = 'https://raw.githubusercontent.com/CRIM-Project/CRIM-online/master/crim/static/mei/MEI_4.0/CRIM_Model_0008.mei'
score = m21.converter.parse(requests.get(path).text)

Load Libraries to Find Particular MEI Elements

import xml.etree.ElementTree as ET
import requests

MEINSURI = 'http://www.music-encoding.org/ns/mei'
MEINS = '{%s}' % MEINSURI


mei_doc = ET.fromstring(requests.get(path).text)
  # Find the title from the MEI file and update the Music21 Score metadata
title = mei_doc.find(f'{MEINS}meiHead//{MEINS}titleStmt/{MEINS}title').text
score.metadata.title = title

mei_doc = ET.fromstring(requests.get(path).text)
  # Find the composer from the MEI file and update the Music21 Score metadata
composer = mei_doc.find(f'{MEINS}meiHead//{MEINS}respStmt/{MEINS}persName').text
score.metadata.composer = composer

View Metadata from music21 Object

print(score.metadata.composer)
print(score.metadata.title)

Josquin Des Prés
Ave Maria

Finding Notes

All the Notes in the all the Voices

This is a truncated view, but illustrates how music21 elements are nested: notes within measures within parts.

voice_parts = score.getElementsByClass(m21.stream.Part)
print(voice_parts.show('text'))

{0.0} <music21.stream.Part 0x7fe0586eb1f0>
    {0.0} <music21.instrument.Instrument '1: [Superius]: '>
    {0.0} <music21.stream.Measure 1 offset=0.0>
        {0.0} <music21.clef.TrebleClef>
        {0.0} <music21.key.Key of C major>
        {0.0} <music21.meter.TimeSignature 4/2>
        {0.0} <music21.stream.Voice 1>
            {0.0} <music21.note.Note G>
            {4.0} <music21.note.Note C>
    {8.0} <music21.stream.Measure 2 offset=8.0>
        {0.0} <music21.stream.Voice 1>
            {0.0} <music21.note.Note C>
            {4.0} <music21.note.Note C>
    {16.0} <music21.stream.Measure 3 offset=16.0>
        {0.0} <music21.stream.Voice 1>
            {0.0} <music21.note.Note D>
            {4.0} <music21.note.Note E>
    {24.0} <music21.stream.Measure 4 offset=24.0>
        {0.0} <music21.stream.Voice 1>
            {0.0} <music21.note.Note C>
    {32.0} <music21.stream.Measure 5 offset=32.0>
        {0.0} <music21.stream.Voice 1>
            {0.0} <music21.note.Rest breve>
    {40.0} <music21.stream.Measure 6 offset=40.0>
        {0.0} <music21.stream.Voice 1>
            {0.0} <music21.note.Rest breve>

List of Voice Parts

To list all the parts, we use score.getElementsByClass(m21.stream.Part):

voice_parts = score.getElementsByClass(m21.stream.Part)
print(voice_parts)

And now iterate over those parts to report the names:

for part in voice_parts:
  print(part.partName)

<music21.stream.iterator.StreamIterator for Score:0x7fe0586ebee0 @:0>
[Superius]
Altus
Tenor
Bassus

Notes from One Voice Part

Define the variable parts and then showing where to obtain these with m21
Define the variable for your staff by index number ([0] is the top voice, [2] is the third from the top, etc.)
The show method, with the parameter text reveals the all the notes found in that part.

parts = score.getElementsByClass(m21.stream.Part)
print(parts[0].show('text'))

{0.0} <music21.instrument.Instrument '1: [Superius]: '>
{0.0} <music21.stream.Measure 1 offset=0.0>
    {0.0} <music21.clef.TrebleClef>
    {0.0} <music21.key.Key of C major>
    {0.0} <music21.meter.TimeSignature 4/2>
    {0.0} <music21.stream.Voice 1>
        {0.0} <music21.note.Note G>
        {4.0} <music21.note.Note C>
{8.0} <music21.stream.Measure 2 offset=8.0>
    {0.0} <music21.stream.Voice 1>
        {0.0} <music21.note.Note C>
        {4.0} <music21.note.Note C>
{16.0} <music21.stream.Measure 3 offset=16.0>
    {0.0} <music21.stream.Voice 1>
        {0.0} <music21.note.Note D>
        {4.0} <music21.note.Note E>
{24.0} <music21.stream.Measure 4 offset=24.0>
    {0.0} <music21.stream.Voice 1>
        {0.0} <music21.note.Note C>
{32.0} <music21.stream.Measure 5 offset=32.0>
    {0.0} <music21.stream.Voice 1>
        {0.0} <music21.note.Rest breve>

"Notes" are Pitch Classes

looking for all the notes in a given part
[X] is index of the given part (so part[0] is the uppermost part in your score)
Note that the code must include flat (as shown below) for reasons that the documentation does not explain!

notes_selected_part = parts[0].flat.getElementsByClass(['Note'])
for note in notes_selected_part:
  print(note)

<music21.note.Note G>
<music21.note.Note C>
<music21.note.Note C>
<music21.note.Note C>
<music21.note.Note D>
<music21.note.Note E>
<music21.note.Note C>
<music21.note.Note C>
<music21.note.Note B>
<music21.note.Note A>
<music21.note.Note G>
<music21.note.Note A>
<music21.note.Note G>
<music21.note.Note C>
<music21.note.Note C>
<music21.note.Note B>
<music21.note.Note A>
<music21.note.Note B>

Printing One Note (and its Attributes)

[x] is zero-based index among the results for the length. So if your number is larger than the number of results, error!
Thus [1] is the second note of that part:

print(notes_selected_part[1])

<music21.note.Note C>

adding .pitch (for instance) tells us class and octave of the note:

print(notes_selected_part[1].pitch)

C5

adding .name (for instance) tells us class alone:

print(notes_selected_part[1].name)

or the .measure number in which the 99th note is found:

print(notes_selected_part[99].measureNumber)

Find Durations (and use with Pandas!)

In music21, each value of 1.0 represents one quarter-note in the score. Thus 2.0 is a half-note (minim), etc.

Must include "flat" for reasons that the documentation does note explain

Here we look for all notes with 2.0 duration in the Tenor part (the third from the top of the score), find the pitch for each, and then make a dictionary of each, which in turn becomes a dataframe:

list_notes = []
notes_tenor = parts[2].flat.getElementsByClass(['Note'])
for note_tenor in notes_tenor:
  if note_tenor.quarterLength == 2.0:  
    note_dict = {'measure' : note_tenor.measureNumber,
                 'pitch' : note_tenor.pitch.name}
    list_notes.append(note_dict)
list_notes


df = pd.DataFrame(list_notes)
df

Rests are not the Same as Notes! Let's Count Them

parts are a submodule, and the getElementsByClass is a method. The particular class we're after is Rest

Here we create a dictionary for each measure/restDuration pair, then add those to a list. The list becomes a dataframe, and we can count the values:

list_rests = []
rests_tenor = parts[2].flat.getElementsByClass(['Rest'])

for tenor_rest in rests_tenor:
    rest_dict = {'measure' : tenor_rest.measureNumber,
                 'duration' : tenor_rest.duration.type}
    list_rests.append(rest_dict)
list_rests
df = pd.DataFrame(list_rests)
df['duration'].value_counts()

breve    34
whole    11
half      1

Pitch (Note in a particular Octave)

here we look for notes in specific octaves, like C4.
parts are a submodule, and the getElementsByClass is a method. The particular class we're after is Notes, and then nameWithOctave

notes_tenor = parts[2].flat.getElementsByClass(['Note'])
for note_tenor in notes_tenor:
  if note_tenor.nameWithOctave == 'C4':  
    print(str(note_tenor.measureNumber) + ": " +note_tenor.nameWithOctave)

5: C4
6: C4
6: C4
8: C4

Intervals

Note the differences:

-pitch is the module (a collection of methods and classes);

Pitch is the class (data structure)

And

interval is part of the pitch module (it's a submodule), and has the method notesToInterval.
Here Interval is another class (data structure), and interval is another module

Here we declare two pitches, the find the interval between them:

pitch_1 = pitch.Pitch('C5')
pitch_2 = pitch.Pitch('G5')
output_interval = interval.Interval(pitch_1, pitch_2)

The name 'with Quality' (for instance Perfect, Major, Minor):

output_interval.name

'P5'

With Quality, written out:

output_interval.niceName

'Perfect Fifth'

Expressed in semintones:

output_interval.semitones

Here we make a list of all the notes in the Tenor, then zip together two lists of adjacent notes. These are in turn used to find the intervals between all successive notes in the voice part. In this case, we print all the different ways of representing the intervals

notes_tenor = parts[2].flat.getElementsByClass(['Note'])
out = zip(notes_tenor,notes_tenor[1:])
for item in out:
    pitch1 = pitch.Pitch(item[0].nameWithOctave)
    pitch2 = pitch.Pitch(item[1].nameWithOctave)
    print(interval.Interval(pitch1, pitch2).directedSimpleName)
    print(interval.Interval(pitch1, pitch2).niceName)
    print(interval.Interval(pitch1, pitch2).name)

P4
Perfect Fourth
P4
P1
Perfect Unison
P1
P1
Perfect Unison
P1
M2
Major Second
M2
M2
Major Second
M2
M-3
Major Third
M3

Sections in this guide

01_Introduction_and_Corpus
02_Notes_Rests
03_Durations
04_TimeSignatures_Beat_Strength
05_Detail_Index
06_Melodic_Intervals
07_Harmonic_Intervals
08_Contrapuntal_Modules
09_Ngrams_Heat_Maps
10_Lyrics_Homorhythm
11_Cadences
12_Presentation_Types
13_Musical_Examples_Verovio
14_Model_Finder
15_Network_Graphs
16_Python_Basics
17_Pandas_Basics
18_Visualizations_Summary
19_Music21_Basics
20_Melodic_Interval_Families
99_Local_Installation

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Music21 Basics

Import the Libraries

Load and Convert MEI to a Music21 object

Load Libraries to Find Particular MEI Elements

View Metadata from music21 Object

Finding Notes

All the Notes in the all the Voices

List of Voice Parts

Notes from One Voice Part

"Notes" are Pitch Classes

Printing One Note (and its Attributes)

Find Durations (and use with Pandas!)

Rests are not the Same as Notes! Let's Count Them

Pitch (Note in a particular Octave)

Intervals

Sections in this guide

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19_Music21_Basics.md

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Music21 Basics

Import the Libraries

Load and Convert MEI to a Music21 object

Load Libraries to Find Particular MEI Elements

View Metadata from music21 Object

Finding Notes

All the Notes in the all the Voices

List of Voice Parts

Notes from One Voice Part

"Notes" are Pitch Classes

Printing One Note (and its Attributes)

Find Durations (and use with Pandas!)

Rests are not the Same as Notes! Let's Count Them

Pitch (Note in a particular Octave)

Intervals

Sections in this guide