How can I produce real-time audio output from music made with Music21?

Question

How can I produce real-time audio output from music made with Music21. Failing that, how can i produce ANY audio output from music made with Music21 via open-source software? Thanks for the help.

Answer 1

As you've seen, music21 isn't designed to be a music playback system, but it IS designed to be embedded within other playback systems or to call them from within the system. We're not planning on putting too much work into playback systems (because of the hardware support, our being a tiny research lab, the work still needing to be done on musical analysis, etc.), but your solution is so elegant that it is now included in all versions of music21 (post v1.1) as the music21.midi.realtime module. Here's an example that takes music21's ability to dynamically allocate midi channels with different pitch-bend objects in order to simulate microtonal playback (a major problem for most midi playback):

#  Set up a detuned piano 
#  (where each key has a random 
#  but consistent detuning from 30 cents flat to sharp)
#  and play a Bach Chorale on it in real time.

from music21 import *
import random
keyDetune = []
for i in range(0, 127):
    keyDetune.append(random.randint(-30, 30))

b = corpus.parse('bach/bwv66.6')
for n in b.flat.notes:
    n.microtone = keyDetune[n.midi]
sp = midi.realtime.StreamPlayer(b)
sp.play()

The StreamPlayer's .play() function can also take busyFunction and busyArgs and busyWaitMilliseconds arguments which specify a function to call with arguments at most every busyWaitMilliseconds (could be more if your system is slower). There is also an endFunction and endArgs that will be called at the end, in case you want to set up some sort of threaded playback. -- Myke Cuthbert (Music21 creator)

Answer 2

So here's what I found out. Here's a python script that works on Windows XP. It needs pygame in addition to music21.

# genPlayM21Score.py Generates and Plays 2 Music21 Scores "on the fly".
#
# see way below for source notes

from music21 import *

# we create the music21 Bottom Part, and do this explicitly, one object at a time.

n1 = note.Note('e4')
n1.duration.type = 'whole'
n2 = note.Note('d4')
n2.duration.type = 'whole'
m1 = stream.Measure()
m2 = stream.Measure()
m1.append(n1)
m2.append(n2)
partLower = stream.Part()
partLower.append(m1)
partLower.append(m2)

# For the music21 Upper Part, we automate the note creation procedure

data1 = [('g4', 'quarter'), ('a4', 'quarter'), ('b4', 'quarter'), ('c#5', 'quarter')]
data2 = [('d5', 'whole')]
data = [data1, data2]
partUpper = stream.Part()

def makeUpperPart(data):
    for mData in data:
        m = stream.Measure()
        for pitchName, durType in mData:
            n = note.Note(pitchName)
            n.duration.type = durType
            m.append(n)
        partUpper.append(m)
makeUpperPart(data)        

# Now, we can add both Part objects into a music21 Score object.  

sCadence = stream.Score()
sCadence.insert(0, partUpper)
sCadence.insert(0, partLower)

# Now, let's play the MIDI of the sCadence Score [from memory, ie no file  write necessary] using pygame

import cStringIO

# for music21 <= v.1.2:
if hasattr(sCadence, 'midiFile'):
   sCadence_mf = sCadence.midiFile
else: # for >= v.1.3:
   sCadence_mf = midi.translate.streamToMidiFile(sCadence)
sCadence_mStr = sCadence_mf.writestr()
sCadence_mStrFile = cStringIO.StringIO(sCadence_mStr)

import pygame

freq = 44100    # audio CD quality
bitsize = -16   # unsigned 16 bit
channels = 2    # 1 is mono, 2 is stereo
buffer = 1024    # number of samples
pygame.mixer.init(freq, bitsize, channels, buffer)

# optional volume 0 to 1.0
pygame.mixer.music.set_volume(0.8)

def play_music(music_file):
    """
    stream music with mixer.music module in blocking manner
    this will stream the sound from disk while playing
    """
    clock = pygame.time.Clock()
    try:
        pygame.mixer.music.load(music_file)
        print "Music file %s loaded!" % music_file
    except pygame.error:
        print "File %s not found! (%s)" % (music_file, pygame.get_error())
        return
    pygame.mixer.music.play()
    while pygame.mixer.music.get_busy():
        # check if playback has finished
        clock.tick(30)

# play the midi file we just saved
play_music(sCadence_mStrFile)

#============================

# now let's make a new music21 Score by reversing the upperPart notes
data1.reverse()
data2 = [('d5', 'whole')]
data = [data1, data2]
partUpper = stream.Part()
makeUpperPart(data)        
sCadence2 = stream.Score()
sCadence2.insert(0, partUpper)
sCadence2.insert(0, partLower)

# now let's play the new Score
sCadence2_mf = sCadence2.midiFile
sCadence2_mStr = sCadence2_mf.writestr()
sCadence2_mStrFile = cStringIO.StringIO(sCadence2_mStr)
play_music(sCadence2_mStrFile)



## SOURCE NOTES
## There are 3 sources for this mashup:

# 1. Source for the Music21 Score Creation http://web.mit.edu/music21/doc/html/quickStart.html#creating-notes-measures-parts-and-scores

# 2.  Source for the Music21 MidiFile Class Behaviour http://mit.edu/music21/doc/html/moduleMidiBase.html?highlight=midifile#music21.midi.base.MidiFile

# 3.  Source for the pygame player: http://www.daniweb.com/software-development/python/code/216979/embed-and-play-midi-music-in-your-code-python