python generating random midi

Published: 29 May 2023
on channel: Claire Sawyer

1,145

ChatGPT is seriously amazing. It assisted me in a random idea of "can i make white midi files on the fly and play them?"... Then then scope creepy inevitably jumped in and I made it choose from musical scales and tried to add a percussion track, but i don't really know much about midi.

def get_scales():
return {
'major': [60,62,64,65,67,69,71,72],
'natural_minor': [60,62,63,65,67,68,70,72],
'harmonic_minor': [60,62,63,65,67,68,71,72],
'melodic_minor': [60,62,63,65,67,69,71,72],
'dorian': [60,62,63,65,67,69,70,72],
'mixolydian': [60,62,64,65,67,69,70,72],
'lydian': [60,62,64,66,67,69,71,72],
'phrygian': [60,61,63,65,67,68,70,72],
'locrian': [60,61,63,64,66,68,70,72],
'pentatonic_major': [60,62,64,67,69,72],
'pentatonic_minor': [60,63,65,67,70,72],
'blues': [60,63,65,66,67,70,72],
'chromatic': [60,61,62,63,64,65,66,67,68,69,70,71,72]
}

def create_random_midi(duration_in_seconds,filename,tempo=500000):
mid = MidiFile()
track = MidiTrack()
mid.tracks.append(track)
track.append(mido.MetaMessage('set_tempo',tempo=tempo))
current_time = 0
beats_per_minute = mido.tempo2bpm(tempo)
seconds_per_beat = 60.0 / beats_per_minute
scales = get_scales()
scale_name = random.choice(list(scales.keys()))
scale = scales[scale_name]
root_note = random.randint(60,72)
scale = [(note - 60) + root_note for note in scale]
if random.choice([True,True,True,False]):
range_increased = True
lower_scale = [note - 12 for note in scale]
higher_scale = [note + 12 for note in scale]
scale = lower_scale + scale + higher_scale
else:
range_increased = False

num_channels = random.randint(2,18)

note_duration_options = [0.1,0.1,0.1,0.1,0.1,0.1,0.1,0.15,0.15,0.15,0.15,0.15,0.25,0.25,0.25,0.25,0.25,0.25,0.25,0.25,0.5,0.5,0.5,0.5,1.0,1.0,1.5,1.5,2.0,2.5]
silence_after_note_options = [0.05,0.05,0.10,0.10,0.15,0.20,0.20,0.25,0.25,0.40,0.50,0.5,0.75]

for channel in range(16):
track = MidiTrack()
if channel != 1: instrument = random.randint(0,127)
track.append(Message('program_change',program=instrument,time=0,channel=channel))
mid.tracks.append(track)
for channel in range(16):
channel_index = channel
while current_time < duration_in_seconds:
num_notes = random.choice([1,2,2,3,3,3,3,4,4])
notes = random.sample(scale,num_notes)
velocity = random.randint(40,120)
note_duration,silence_after_note = random.choice(note_duration_options),random.choice(silence_after_note_options)

for note in notes:
message = Message('note_on',note=note,velocity=velocity,time=0,channel=channel)
mid.tracks[channel_index].append(message)

for note in notes:
message = Message('note_off',note=note,velocity=velocity,time=int(seconds_per_beat * mido.second2tick(note_duration,mid.ticks_per_beat,tempo)),channel=channel)
mid.tracks[channel_index].append(message)
current_time += note_duration

mid.tracks[channel_index].append(Message('note_off',note=0,velocity=0,time=int(seconds_per_beat * mido.second2tick(silence_after_note,mid.ticks_per_beat,tempo))))
current_time += silence_after_note

mid = add_random_drums(mid,duration_in_seconds,tempo)
mid.save(filename)

def add_random_drums(midi_file,duration_in_seconds,tempo=500000):

if len(midi_file.tracks) > 9:
track = midi_file.tracks[9]
track.clear()
else:
track = MidiTrack()
midi_file.tracks.append(track)

beats_per_minute = mido.tempo2bpm(tempo)
seconds_per_beat = 60.0 / beats_per_minute

drum_notes = [36,36,36,38,42,42,42,42,46,46,46,46,]
drum_pattern_duration_options = [0.25,0.5,1.0]

current_time = 0
while current_time < duration_in_seconds:
drum_note = random.choice(drum_notes)
velocity = random.randint(40,120)
pattern_duration = random.choice(drum_pattern_duration_options)
message_on = Message('note_on',note=drum_note,velocity=velocity,time=0,channel=10)
track.append(message_on)
message_off = Message('note_off',note=drum_note,velocity=velocity,time=int(seconds_per_beat * mido.second2tick(pattern_duration,midi_file.ticks_per_beat,tempo)),channel=10)
track.append(message_off)
current_time += pattern_duration
return midi_file

def main():
if len(sys.argv) < 2: raise Exception("Usage: python script.py <output_filename> [<song_length_in_seconds>]")
filename = sys.argv[1]

length = ""
if len(sys.argv) > 2: length = int(sys.argv[2])
create_random_midi(length,filename)

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