An Introduction to Symbolic Music Processing with Partitura

Partitura is python 3 package for symbolic music processing developed and maintained at CP JKU Linz (and other contributors). It’s intended to give a lightweight musical part representation that makes many score properties easily accessible for a variety of tasks. Furthermore, it’s a very useful I/O utility to parse computer formats of symbolic music.

1. Install and import

Partitura is available in github https://github.com/CPJKU/partitura

You can install it with pip install partitura.

However if you are interested in features that still have to be officially released, it’s better to install the develop branch.

try:
    import google.colab
    IN_COLAB = True
except:
    IN_COLAB = False

if IN_COLAB:
    # Install partitura
    ! pip install partitura
else:
    pass

import glob
import os
import partitura as pt
import numpy as np
import matplotlib.pyplot as plt
import os
os.environ['KMP_DUPLICATE_LIB_OK']='True'
import IPython.display as ipd

Dataset for this tutorial

In this tutorial we are going to use the Vienna 4x22 Corpus which consists of performances of 4 classical piano pieces, which have been aligned to their corresponding scores.

The dataset contains:

• Scores in MusicXML format (4 scores)

• Performances in MIDI files (88 in total, 22 performances per piece, each by a different pianist)

• Score to performance alignments in Match file format (88 in total one file per performance)

# setup the dataset
if IN_COLAB:
    !git clone https://github.com/CPJKU/vienna4x22.git
    DATASET_DIR = "./vienna4x22"
    MUSICXML_DIR = os.path.join(DATASET_DIR, 'musicxml')
    MIDI_DIR = os.path.join(DATASET_DIR, 'midi')
    MATCH_DIR = os.path.join(DATASET_DIR, 'match')
else:
    import sys, os
    sys.path.append(os.path.join(os.path.dirname(os.path.dirname(os.getcwd())), "utils"))
    from load_data import init_dataset
    DATASET_DIR = init_dataset()
    MUSICXML_DIR = os.path.join(DATASET_DIR, 'musicxml')
    MIDI_DIR = os.path.join(DATASET_DIR, 'midi')
    MATCH_DIR = os.path.join(DATASET_DIR, 'match')

2. Loading and Exporting Files

One of the main use cases of partitura is to load and export common symbolic music formats.

Reading

Symbolic Scores

These methods return Score objects.

Format	Method	Notes
Any Symbolic Format	part itura.loa d_score	(MIDI, MusicXML, MIDI, MEI, Kern)
MusicXML	partitu ra.load_m usicxml
MIDI	`` partitura .load_sco re_midi``	Pitch spelling, key signature (optional) and other information is inferred with methods in partitura.musicanalysis.
MEI	pa rtitura.l oad_mei
Humdrum Kern	par titura.lo ad_kern
MuseScore	par titura.lo ad_via_mu sescore	Requires MuseScore. Loads all formats supported by MuseScore. Support on Windows is still untested.

Symbolic Performances

These methods return a Performance.

Format	Method	Notes
MIDI	partitura.load_performance_midi	Loads MIDI file as a performance, including track, channel and program information. Time signature and tempo information are only used to compute the time of the MIDI messages in seconds. Key signature information is ignored

Alignments

These methods return score-to-performance alignments (discussed in another notebook).

Format	Method	Notes
Match file	partitura.load_match	Returns alignment, a performance as PerformedPart and optionally a Part. See usage below.
Nakamura et al. corresp file	partitura.load_nakamuracorresp
Nakamura et al. match file	partitura.load_nakamuramatch

Writing

Symbolic Scores

Format	Method	Notes
MusicXML	partitura.save_musicxml
MIDI	partitura.save_score_midi	Includes Key signature, time signature and tempo information.

Symbolic Performances

Format	Method	Notes
MIDI	partitura.save_performance_midi	Does not include key signature or time signature information

Alignments

Format	Method	Notes
Match file	partitura.save_match

3. Internal Representations

Score loading functions return a Score object. It’s a wrapper storing score metadata such as composer and piece as well as all musical material in the score. At the same time it acts as an iterator of contained Part objects.

The Part object is the central object of partitura. Its name stems from musicxml parts and usually a single instrument. - it is a timeline object - time is measured in divs - its elements are timed objects, i.e. they have a starting time and an ending time - external score files are loaded into a part - parts can be exported into score files - it contains many useful methods related to its properties

Here’s a visual representation of the Part object representing the first measure of Chopin’s Nocturne Op. 9 No. 2

path_to_musicxml = pt.EXAMPLE_MUSICXML
part = pt.load_musicxml(path_to_musicxml)[0] # we access the first (and sole) part of this score by indexing the returned score
print(part.pretty())

Part id="P1" name="Piano"
 │
 ├─ TimePoint t=0 quarter=12
 │   │
 │   └─ starting objects
 │       │
 │       ├─ 0--48 Measure number=1 name=1
 │       ├─ 0--48 Note id=n01 voice=1 staff=2 type=whole pitch=A4
 │       ├─ 0--48 Page number=1
 │       ├─ 0--24 Rest id=r01 voice=2 staff=1 type=half
 │       ├─ 0--48 System number=1
 │       └─ 0-- TimeSignature 4/4
 │
 ├─ TimePoint t=24 quarter=12
 │   │
 │   ├─ ending objects
 │   │   │
 │   │   └─ 0--24 Rest id=r01 voice=2 staff=1 type=half
 │   │
 │   └─ starting objects
 │       │
 │       ├─ 24--48 Note id=n02 voice=2 staff=1 type=half pitch=C5
 │       └─ 24--48 Note id=n03 voice=2 staff=1 type=half pitch=E5
 │
 └─ TimePoint t=48 quarter=12
     │
     └─ ending objects
         │
         ├─ 0--48 Measure number=1 name=1
         ├─ 0--48 Note id=n01 voice=1 staff=2 type=whole pitch=A4
         ├─ 24--48 Note id=n02 voice=2 staff=1 type=half pitch=C5
         ├─ 24--48 Note id=n03 voice=2 staff=1 type=half pitch=E5
         ├─ 0--48 Page number=1
         └─ 0--48 System number=1

Each Part object contains a list notes. Notes inherit from the TimedObject class. Like all TimedObjects they contain a (possibly coincident) start time and end time, encoded as TimePoint objects.

part.notes

[<partitura.score.Note at 0x1eebfb58af0>,
 <partitura.score.Note at 0x1eebfb40b20>,
 <partitura.score.Note at 0x1eebfb40ca0>]

# uncomment to print all note object attributes
# dir(part.notes[0])

You can create notes (without timing information) and then add it to a part by specifying start and end times (in divs!). Use each note object only once! You can remove notes from a part.

a_new_note = pt.score.Note(id='n04', step='A', octave=4, voice=1)
part.add(a_new_note, start=3, end=15)
# print(part.pretty())

part.remove(a_new_note)
# print(part.pretty())

Integer divs are useful for encoding scores but unwieldy for human readers. Partitura offers a variety of *unit*_maps from the timeline unit "div" to musical units such as "beats" (in two different readings) or "quarters". For the inverse operation the corresponding inv_*unit*_map exist as well. Quarter to div ratio is a fixed value for a Part object, but units like beats might change with time signature, so these maps are implemented as Part methods.

Let’s look at how to get the ending position in beats of the last note in our example Part.

part.beat_map(part.notes[0].end.t)

array(4.)

For several TimedObjects partitura offers convenient maps that return the object at a position, usually given in divs. Other musical information such as key and time signature is valid for a segment of the score but only encoded in one location. Maps also retrieve the "currently active" time or key signature at any score position.

Returns	Method	Notes
Time Signature	part.time_signature_map	return a triple of beats, beat_type, and musical_beats
Key Signature	part.key_signature_map
Measure	part.measure_map	returns the start and end point of the current measure
Measure Number	part.measure_number_map
Metrical Position	part.metrical_position_map
Divs -> Beat	part.beat_map
Beat -> Divs	part.inv_beat_map
Divs -> Quarters	part.quarter_map
Quarter -> Divs	part.inv_quarter_map
Quarter Durations	part.quarter_duration_map

Each Part object contains a central method iter_all to iterate over all instances of the TimedObject class or its subclasses of a part. The iter_all method returns an iterator and takes five optional parameters: - A TimedObject subclass whose instances are returned. You can find them all in the partitura/partitura/score.py file. Default is all classes. - A include_subclasses flag. If true, instances of subclasses are returned too. E.g. part.iter_all(pt.score.TimedObject, include_subclasses=True) returns all objects or part.iter_all(pt.score.GenericNote, include_subclasses=True) returns all notes (grace notes, standard notes) - A start time in divs to specify the search interval (default is beginning of the part) - An end time in divs to specify the search interval (default is end of the part) - A mode parameter to define whether to search for starting or ending objects, defaults to starting.

for measure in part.iter_all(pt.score.Measure):
    print(measure)

0--48 Measure number=1 name=1

for note in part.iter_all(pt.score.GenericNote, include_subclasses=True, start=0, end=24):
    print(note)

0--48 Note id=n01 voice=1 staff=2 type=whole pitch=A4
0--24 Rest id=r01 voice=2 staff=1 type=half

For several TimedObjects partitura offers convenient retrieval functions that return the a list of that object without having to use the general part.iter_all.

Returns	Method	Notes
Notes	part.notes
Tied Notes	part.notes_tied	Tied notes are merged into a single sounding note
Measures	part.measures
Rests	part.rests
Repeats	part.repeats
Key Signatures	part.key_sigs
Time Signatures	part.time_sigs
Dynamics	part.dynamics	Dynamics markings in the score
Articulations	part.articulations	Articulation markings in the score

Let’s use class retrieval, time mapping, and object creation together and add a new measure with a single beat-length note at its downbeat. This code works even if you know nothing about the underlying score.

# figure out the last measure position, time signature and beat length in divs
measures = [m for m in part.iter_all(pt.score.Measure)]
last_measure_number = measures[-1].number
append_measure_start =  measures[-1].end.t
Last_measure_ts = part.time_signature_map(append_measure_start)

Last_measure_ts = part.time_signature_map(append_measure_start)
one_beat_in_divs_at_the_end = append_measure_start - part.inv_beat_map(part.beat_map(append_measure_start)-1)
append_measure_end = append_measure_start +  one_beat_in_divs_at_the_end*Last_measure_ts[0]

# add a measure
a_new_measure = pt.score.Measure(number = last_measure_number+1)
part.add(a_new_measure, start=append_measure_start, end=append_measure_end)
# add a note
a_new_note = pt.score.Note(id='n04', step='A', octave=4, voice=1)
part.add(a_new_note, start=append_measure_start, end=append_measure_start+one_beat_in_divs_at_the_end)

# print(part.pretty())

Now that we know the basics of partitura internals we use some randomization to create random scores, that are nevertheless fully specified and exportable to musicxml.

def addnote(midipitch, part, voice, start, end, idx):
    """
    adds a single note by midipitch to a part
    """
    step, alter, octave = pt.utils.music.midi_pitch_to_pitch_spelling(midipitch)

    part.add(pt.score.Note(id='n{}'.format(idx), step=step,
                        octave=int(octave), alter=alter, voice=voice, staff=int((voice-1)%2+1)),
                        start=start, end=end)

l = 100
p = pt.score.Part('cat_on_keyboard', 'Cat on Keyboard', quarter_duration=8)
dur = np.random.randint(1,20, size=(4,l))
ons = np.cumsum(np.concatenate((np.zeros((4,1)),dur), axis=1), axis = 1)
pitch = np.row_stack((np.random.randint(70,80, size=(1,l)),
                      np.random.randint(50,60, size=(1,l)),
                      np.random.randint(60,70, size=(1,l)),
                      np.random.randint(40,50, size=(1,l))
                     ))

for k in range(l):
    for j in range(4):
        addnote(pitch[j,k], p, j+1, ons[j,k], ons[j,k]+dur[j,k], "v"+str(j)+"n"+str(k))

# sanitize the part
p.add(pt.score.TimeSignature(4, 4), start=0)
p.add(pt.score.Clef(1, "G", line = 3, octave_change=0),start=0)
p.add(pt.score.Clef(2, "F", line = 4, octave_change=0),start=0)
pt.score.add_measures(p)
pt.score.tie_notes(p)

# pt.save_score_midi(p, "CatPerformance.mid", part_voice_assign_mode=2)

# pt.save_musicxml(p, "CatScore.musicxml")

pr = pt.utils.compute_pianoroll(p)
fig, ax = plt.subplots(1, figsize=(8, 2))
ax.imshow(pr.toarray()[35:85,:500], origin="lower", cmap='gray', interpolation='nearest', aspect='auto')
plt.show()

SAMPLE_RATE = 11025

audio_p = pt.utils.synth.synthesize(note_info=p, samplerate=SAMPLE_RATE, harmonic_dist=10, bpm=180)
ipd.display(ipd.Audio(data=audio_p, rate=SAMPLE_RATE, normalize=False))

Performance loading functions return a Performance object. It’s a wrapper storing performance metadata as well as all information of a MIDI file. At the same time it acts as an iterator of contained PerformedPart objects.

The PerformedPart class is a wrapper for MIDI tracks. Its structure is much simpler than the Part object’s: - a notes property that consists of list of MIDI notes as dictionaries - a controls property that consists of list of MIDI CC messages - some more utility methods and properties, such as program changes, note array, and others.

path_to_midifile = pt.EXAMPLE_MIDI
# as for scores we index the performance to retrieve the first (and sole) performedpart
performedpart = pt.load_performance_midi(path_to_midifile)[0]

performedpart.notes

[<partitura.performance.PerformedNote at 0x1eec05af910>,
 <partitura.performance.PerformedNote at 0x1eec05af490>,
 <partitura.performance.PerformedNote at 0x1eec05afa60>]

4. Extracting Information from Scores and Performances

For many MIR tasks we need to extract specific information out of scores or performances. Two of the most common representations are note arrays and piano rolls (note that there is some overlap in the way that these terms are used in the literature).

Partitura provides convenience methods to extract these common features in a few lines!

To estimate even higher level information, partitura offers implementations of standard methods in automatic music analysis.

A note array is a 2D array in which each row represents a note in the score/performance and each column represents different attributes of the note.

In partitura, note arrays are structured numpy arrays, which are ndarrays in which each "column" has a name, and can be of different datatypes. This allows us to hold information that can be represented as integers (MIDI pitch/velocity), floating point numbers (e.g., onset time) or strings (e.g., note ids).

In this tutorial we are going to cover 3 main cases

• Getting a note array from Part and PerformedPart objects

• Extra information and alternative ways to generate a note array

• Creating a custom note array from scratch from a Part object

# Path to the MusicXML file
score_fn = os.path.join(MUSICXML_DIR, 'Chopin_op38.musicxml')

# Load the score into a `Score` object
score = pt.load_musicxml(score_fn)

# Get note array. Calling note arrays from scores will merge the contained parts' note arrays into one.
score_note_array = score.note_array()

It is that easy!

# Lets see the first notes in this note array
print(score_note_array[:10])

[(-4., 1., -2. , 0.5,  0,  8, 60, 4, 'n2', 16)
 (-4., 1., -2. , 0.5,  0,  8, 72, 1, 'n1', 16)
 (-3., 2., -1.5, 1. ,  8, 16, 60, 4, 'n4', 16)
 (-3., 2., -1.5, 1. ,  8, 16, 72, 1, 'n3', 16)
 (-1., 1., -0.5, 0.5, 24,  8, 60, 4, 'n6', 16)
 (-1., 1., -0.5, 0.5, 24,  8, 72, 1, 'n5', 16)
 ( 0., 2.,  0. , 1. , 32, 16, 60, 4, 'n8', 16)
 ( 0., 2.,  0. , 1. , 32, 16, 72, 1, 'n7', 16)
 ( 2., 1.,  1. , 0.5, 48,  8, 60, 4, 'n10', 16)
 ( 2., 1.,  1. , 0.5, 48,  8, 72, 1, 'n9', 16)]

By default, Partitura includes some of the most common note-level information in the note array:

print(score_note_array.dtype.names)

('onset_beat', 'duration_beat', 'onset_quarter', 'duration_quarter', 'onset_div', 'duration_div', 'pitch', 'voice', 'id', 'divs_pq')

• onset_beat is the onset time in beats (as indicated by the time signature). In partitura, negative onset times in beats represent pickup measures. Onset time 0 is the start of the first measure.

• duration_beat is the duration of the note in beats

• onset_quarter is the onset time of the note in quarters (independent of the time signature). Similarly to onset time in beats, negative onset times in quarters represent pickup measures and onset time 0 is the start of the first measure.

• duration_quarteris the duration of the note in quarters

• onset_div is the onset of the note in divs, which is generally a number that allows to represent the note position and duration losslessly with integers. In contrast to onset time in beats or quarters, onset time in divs always start at 0 at the first "element" in the score (which might not necessarily be a note).

• duration_div is the duration of the note in divs.

• pitch is the MIDI pitch (MIDI note number) of the note

• voice is the voice of the note (in polyphonic music, where there can be multiple notes at the same time)

• id is the note id (as appears in MusicXML or MEI formats)

# Path to the MIDI file
performance_fn = os.path.join(MIDI_DIR, 'Chopin_op38_p01.mid')

# Loading the file to a PerformedPart
performance = pt.load_performance_midi(performance_fn)

# Get note array!
performance_note_array = performance.note_array()

Since performances contain have other information not included in scores, the default fields in the note array are a little bit different:

print(performance_note_array.dtype.names)

('onset_sec', 'duration_sec', 'onset_tick', 'duration_tick', 'pitch', 'velocity', 'track', 'channel', 'id')

• onset_sec is the onset time of the note in seconds. Onset time in seconds is always \(\geq 0\) (otherwise, the performance would violate the laws of physics ;)

• duration_sec is the duration of the note in seconds

• onset_tick is the onset time of the note in MIDI ticks.

• duration_tick is the duration of the note in MIDI ticks

• pitch is the MIDI pitch

• velocity is the MIDI velocity

• track is the track number in the MIDI file

• channel is the channel in the MIDI file

• id is the ID of the notes (automatically generated for MIDI file according to onset time)

print(performance_note_array[:5])

[(5.6075 , 0.12625, 44860, 1010, 72, 37, 0, 0, 'P00_n0')
 (5.63375, 0.0975 , 45070,  780, 60, 27, 0, 0, 'P00_n1')
 (6.07   , 0.21625, 48560, 1730, 72, 45, 0, 0, 'P00_n2')
 (6.11125, 0.2525 , 48890, 2020, 60, 26, 0, 0, 'P00_n3')
 (6.82625, 0.17   , 54610, 1360, 60, 39, 0, 0, 'P00_n4')]

# Get a note_array with notes played on your computer keyboard:
# ----------> https://editor.p5js.org/oemei/full/6nux_mRgT
# replace the note array below with the generated code:
note_array = np.array(
    [(60, 0, 2, 40),
     (66, 2, 1, 80)],
    dtype=[("pitch", "i4"),
           ("onset_sec", "f4"),
           ("duration_sec", "f4"),
           ("velocity", "i4"),
          ]
)
# Note array to `PerformedPart`
performed_part = pt.performance.PerformedPart.from_note_array(note_array)

We can then export the PerformedPart directly to a MIDI file!

# export as MIDI file
# pt.save_performance_midi(performed_part, "example.mid")

Sometimes we require more information in a note array. The simplest solutions is to pass a number of argument flags for additional fields.

extended_score_note_array = pt.utils.music.ensure_notearray(
    score,
    include_pitch_spelling=True, # adds 3 fields: step, alter, octave
    include_key_signature=True, # adds 2 fields: ks_fifths, ks_mode
    include_time_signature=True, # adds 2 fields: ts_beats, ts_beat_type
    include_metrical_position=True, # adds 3 fields: is_downbeat, rel_onset_div, tot_measure_div
    include_grace_notes=True # adds 2 fields: is_grace, grace_type
)

extended_score_note_array.dtype.names

('onset_beat',
 'duration_beat',
 'onset_quarter',
 'duration_quarter',
 'onset_div',
 'duration_div',
 'pitch',
 'voice',
 'id',
 'step',
 'alter',
 'octave',
 'is_grace',
 'grace_type',
 'ks_fifths',
 'ks_mode',
 'ts_beats',
 'ts_beat_type',
 'ts_mus_beats',
 'is_downbeat',
 'rel_onset_div',
 'tot_measure_div',
 'divs_pq')

print(extended_score_note_array[['id',
                                 'step',
                                 'alter',
                                 'octave',
                                 'ks_fifths',
                                 'ks_mode',
                                 'is_downbeat']][:10])

[('n2', 'C', 0, 4, -1, 1, 0) ('n1', 'C', 0, 5, -1, 1, 0)
 ('n4', 'C', 0, 4, -1, 1, 0) ('n3', 'C', 0, 5, -1, 1, 0)
 ('n6', 'C', 0, 4, -1, 1, 0) ('n5', 'C', 0, 5, -1, 1, 0)
 ('n8', 'C', 0, 4, -1, 1, 1) ('n7', 'C', 0, 5, -1, 1, 1)
 ('n10', 'C', 0, 4, -1, 1, 0) ('n9', 'C', 0, 5, -1, 1, 0)]

Note arrays can further be extended with note features. Note features are musical attributes that can be retrieved by built-in helper functions. See a list of avaliable note feature functions by calling partitura.musicanalysis.list_note_feats_functions. Pass a list of chosen note features to partitura.compute_note_array to compute an extended note array.

pt.musicanalysis.list_note_feats_functions()

['articulation_direction_feature',
 'articulation_feature',
 'duration_feature',
 'fermata_feature',
 'grace_feature',
 'loudness_direction_feature',
 'metrical_feature',
 'metrical_strength_feature',
 'onset_feature',
 'ornament_feature',
 'polynomial_pitch_feature',
 'relative_score_position_feature',
 'slur_feature',
 'staff_feature',
 'tempo_direction_feature',
 'time_signature_feature',
 'vertical_neighbor_feature']

pt.compute_note_array(score, feature_functions=[
 'metrical_feature',
 'metrical_strength_feature'
                      ])[:10]

array([('n2', -4., 1., -2. , 0.5,  0,  8, 60, 4, 1., 0., 0., 0., 0., 0., 0., 0.33333334, 0., 0., 0.),
       ('n1', -4., 1., -2. , 0.5,  0,  8, 72, 1, 1., 0., 0., 0., 0., 0., 0., 0.33333334, 0., 0., 0.),
       ('n4', -3., 2., -1.5, 1. ,  8, 16, 60, 4, 0., 1., 0., 0., 0., 0., 0., 0.5       , 0., 1., 0.),
       ('n3', -3., 2., -1.5, 1. ,  8, 16, 72, 1, 0., 1., 0., 0., 0., 0., 0., 0.5       , 0., 1., 0.),
       ('n6', -1., 1., -0.5, 0.5, 24,  8, 60, 4, 0., 0., 1., 0., 0., 0., 0., 0.8333333 , 0., 0., 0.),
       ('n5', -1., 1., -0.5, 0.5, 24,  8, 72, 1, 0., 0., 1., 0., 0., 0., 0., 0.8333333 , 0., 0., 0.),
       ('n8',  0., 2.,  0. , 1. , 32, 16, 60, 4, 1., 0., 0., 0., 0., 0., 0., 0.        , 1., 0., 1.),
       ('n7',  0., 2.,  0. , 1. , 32, 16, 72, 1, 1., 0., 0., 0., 0., 0., 0., 0.        , 1., 0., 1.),
       ('n10',  2., 1.,  1. , 0.5, 48,  8, 60, 4, 0., 0., 0., 1., 0., 0., 0., 0.33333334, 0., 0., 0.),
       ('n9',  2., 1.,  1. , 0.5, 48,  8, 72, 1, 0., 0., 0., 1., 0., 0., 0., 0.33333334, 0., 0., 0.)],
      dtype=[('id', '<U256'), ('onset_beat', '<f4'), ('duration_beat', '<f4'), ('onset_quarter', '<f4'), ('duration_quarter', '<f4'), ('onset_div', '<i4'), ('duration_div', '<i4'), ('pitch', '<i4'), ('voice', '<i4'), ('metrical_feature.metrical_6_8_0', '<f4'), ('metrical_feature.metrical_6_8_1', '<f4'), ('metrical_feature.metrical_6_8_3', '<f4'), ('metrical_feature.metrical_6_8_2', '<f4'), ('metrical_feature.metrical_6_8_5', '<f4'), ('metrical_feature.metrical_6_8_weak', '<f4'), ('metrical_feature.metrical_6_8_4', '<f4'), ('metrical_strength_feature.beat_phase', '<f4'), ('metrical_strength_feature.metrical_strength_downbeat', '<f4'), ('metrical_strength_feature.metrical_strength_secondary', '<f4'), ('metrical_strength_feature.metrical_strength_weak', '<f4')])

Sometimes we are interested in other note-level information that is not included in the standard note features. With partitura we can create such a custom note array easily!

For example, imagine that we want a note array that includes whether the notes have an accent mark.

# Path to the MusicXML file
score_fn = os.path.join(MUSICXML_DIR, 'Chopin_op10_no3.musicxml')

# Load the score into a `Part` object
score_part = pt.load_musicxml(score_fn)[0]

def get_accent_note_array(part):

    fields = [("onset_beat", "f4"),
              ("pitch", "i4"),
              ("accent", "i4")]
    # Get all notes in the part
    notes = part.notes_tied
    # Beat map (maps divs to score time in beats)
    beat_map = part.beat_map
    N = len(notes)
    note_array = np.zeros(N, dtype=fields)
    for i, n in enumerate(notes):
        # MIDI pitch
        note_array[i]['pitch'] = n.midi_pitch
        # Get the onset time in beats
        note_array[i]['onset_beat'] = beat_map(n.start.t)

        # Iterate over articulations in the note
        if n.articulations:
            for art in n.articulations:
                if art == 'accent':
                    note_array[i]['accent'] = 1
    return note_array

accent_note_array = get_accent_note_array(score_part)

accented_note_idxs = np.where(accent_note_array['accent'])
print(accent_note_array[accented_note_idxs][:5])

[(0.25, 47, 1) (1.25, 47, 1) (2.25, 47, 1) (3.  , 68, 1) (3.25, 47, 1)]

Piano rolls are 2D matrices that represent pitch and time information. The time represents time steps (at a given resolution), while the pitch axis represents which notes are active at a given time step. We can think of piano rolls as the symbolic equivalent of spectrograms.

Extracting a piano roll

score_fn = os.path.join(MUSICXML_DIR, 'Chopin_op10_no3.musicxml')
score = pt.load_musicxml(score_fn)
pianoroll = pt.utils.compute_pianoroll(score)

The compute_pianoroll method has a few arguments to customize the resulting piano roll

piano_range = True
time_unit = 'beat'
time_div = 10
pianoroll = pt.utils.compute_pianoroll(
    note_info=score, # a `Score`, `Performance`, `Part`, `PerformedPart` or a note array
    time_unit=time_unit, # beat, quarter, div, sec, etc. (depending on note_info)
    time_div=time_div, # Number of cells per time unit
    piano_range=piano_range # Use range of the piano (88 keys)
)

An important thing to remember is that in piano rolls generated by compute_pianoroll, rows (the vertical axis) represent the pitch dimension and the columns (horizontal) the time dimension. This results in a more intuitive way of plotting the piano roll. For other applications the transposed version of this piano roll might be more useful (i.e., rows representing time steps and columns representing pitch information).

Since piano rolls can result in very large matrices where most of the elements are 0, the output of compute_pianoroll is a scipy sparse matrix. To convert it to a regular numpy array, we can simply use pianoroll.toarray()

Let’s plot the piano roll!

fig, ax = plt.subplots(1, figsize=(20, 10))
ax.imshow(pianoroll.toarray(), origin="lower", cmap='gray', interpolation='nearest', aspect='auto')
ax.set_xlabel(f'Time ({time_unit}s/{time_div})')
ax.set_ylabel('Piano key' if piano_range else 'MIDI pitch')
plt.show()

In some cases, we want to know the "coordinates" of each of the notes in the piano roll. The compute_pianoroll method includes an option to return

pianoroll, note_indices = pt.utils.compute_pianoroll(score_part, return_idxs=True)

# MIDI pitch, start, end
print(note_indices[:5])

[[59  0  4 59]
 [40  4  6 40]
 [40  4 12 40]
 [56  4  6 56]
 [64  4  8 64]]

Generating a note array from a piano roll

Partitura also includes a method to generate a note array from a piano roll, which can be used to generate a MIDI file. This method would be useful, e.g., for music generation tasks

pianoroll = pt.utils.compute_pianoroll(score_part)

new_note_array = pt.utils.pianoroll_to_notearray(pianoroll)

# We can export the note array to a MIDI file
ppart = pt.performance.PerformedPart.from_note_array(new_note_array)

# pt.save_performance_midi(ppart, "newmidi.mid")

Automatic music analysis is one of the main areas where partitura pipelines are useful. Furthermore, for comparison and non-state-of-the-art applications partitura also provides baseline algorithms for several music analysis tasks:

Returns	Method	Notes
Voices	partitura.musicanalysis.estimate_voices	Estimate each note’s voice
Key	partitura.musicanalysis.estimate_key
Pitch Spelling	partitura.musicanalysis.estimate_spelling	Infer correct pitch spelling from MIDI pitches
Tonal Tension	partitura.musicanalysis.estimate_tonaltension
Meter, Beats, Tempo	partitura.musicanalysis.estimate_time

The end of the tutorial, the start of your yet untold adventures in symbolic music processing…

Thank you for trying out partitura! We hope it serves you well.

If you miss a particular functionality or encounter a bug, we appreciate it if you raise an issue on github: Github Issues