This skill provides tools and patterns for music composition, not pre-baked solutions. The intelligence and music21 library should be used to compose dynamically based on user requests.

Core Principle: Write custom code that composes music algorithmically rather than calling functions with hardcoded melodies.

Installation & Setup

Quick Installation

Run the automated installer for complete setup: install.sh . This installs all system dependencies, Python packages, and verifies the installation.

Note: The install script may display "error: externally-managed-environment" messages at the end. These are expected and can be safely ignored - the dependencies are already installed. If such messages appear, the installation was successful.

Available SoundFonts

Traditional Pipeline (Orchestral/Acoustic):

/usr/share/sounds/sf2/FluidR3_GM.sf2 (141MB, General MIDI soundfont - use for high-quality orchestral/acoustic samples)
/usr/share/sounds/sf2/default.sf2 (symlink to best available)
⚠️ DO NOT use TimGM6mb.sf2 - inferior quality, guitars sound electronic/piano-like

Electronic Pipeline:

Uses the same FluidR3_GM.sf2 soundfont as traditional music
The difference is which GM programs you choose (synth programs 38-39, 80-95 instead of orchestral)

Key Concepts

Always create downloadable MP3 files (not HTML players)
music21.instrument classes can be used for convenience: instrument.Violin() , instrument.Violoncello() , instrument.Piano() , instrument.Trumpet() , etc.
CRITICAL: ALWAYS use mido to set MIDI program numbers after export - music21's instrument classes do NOT reliably export program_change messages. See the mido workflow below.
Generate notes programmatically - avoid hardcoded sequences

Choosing Your Music Generation Pipeline

This skill supports TWO rendering pipelines optimized for different musical styles. Read the user's request carefully and choose the correct pipeline by reading the correct next file.

Decision Process

Identify from the user's request:

Genre keywords (house, techno, classical, orchestral, reggae)
Instrument references (synthesizers vs acoustic instruments)
Musical style descriptions (electronic/DJ vs traditional/acoustic)
Artist mentions (DJs vs classical composers)

Electronic Pipeline

Use electronic-music-pipeline.md when request includes:

Genres: House, techno, trance, EDM, electronic dance music, ambient electronic, acid house, deep house, club music, DJ sets
Instruments: Synthesizers, synth bass/pads/leads, 808 drums, electronic drums, supersaw leads, sub-bass
Context: References to DJs (Keinemusik, Black Coffee, Avicii, Swedish House Mafia), BPM 120-140, "for a club", "for dancing"
Sound descriptions: "Fat synth sound", "buzzy leads", "electronic", "synth-heavy"

How it works:

Uses real-time synthesis (no soundfonts)
Synthesizes drums, bass, pads, leads on-the-fly with DSP
Genre presets optimize synthesis parameters (deep_house, techno, trance, ambient, acid_house)
Frequency-aware mixing automatically balances low/mid/high frequencies
Best for: Authentic electronic sounds, modern EDM production

→ See electronic-music-pipeline.md for detailed instructions

Traditional Pipeline

Use traditional-music-pipeline.md when request includes:

Genres: Classical, orchestral, jazz, blues, rock, country, folk, reggae, ska, symphonic, chamber music
Instruments: Violin, cello, trumpet, flute, piano, acoustic guitar, acoustic bass, brass ensembles, string quartets, organ (reggae/gospel)
Context: References to composers (Mozart, Beethoven, Bach), classical periods (Baroque, Romantic), "unplugged", "acoustic version"
Sound descriptions: "Traditional", "acoustic", "orchestral"

How it works:

Uses pre-recorded orchestral samples (soundfonts)
FluidR3_GM.sf2 soundfont with 128 General MIDI instruments
Good for realistic orchestral/acoustic instruments
Best for: Classical, jazz, reggae, rock, traditional music

→ See traditional-music-pipeline.md for detailed instructions

If Unclear

Default to TRADITIONAL for mixed requests or ambiguous genres
Ask user for clarification if request could go either way

Why This Matters

Using wrong pipeline = poor audio quality (technically works, sounds bad)
Electronic pipeline: Real-time synthesis for authentic electronic sounds
Traditional pipeline: Pre-recorded samples for realistic orchestral/acoustic

Available Scripts

All scripts are located in ./scripts :

Traditional Rendering:

midi_inventory.py
Extract complete structure from ANY MIDI file to JSON format
midi_render.py
Render JSON music structure to MP3 using FluidSynth with dynamic range compression
midi_utils.py
MIDI utility functions (extract drums, get BPM, etc.)

Utilities:

audio_validate.py
Validate audio file quality and format

Note: Both electronic and traditional music use the same rendering pipeline (FluidSynth + FluidR3_GM.sf2). The difference is which GM programs you choose.

Music Theory Reference

Complete General MIDI Instrument Map (Programs 0-127)

CRITICAL: music21 does NOT reliably export program_change messages. You MUST ALWAYS use mido to set program numbers after export, even for traditional instruments like saxophone, guitar, or bass. Without this step, tracks will default to piano (program 0).

INSTRUMENT CATEGORIZATION FOR SYNTHESIS: When composing electronic music, classify instruments by their sonic characteristics for proper synthesis:

Guitar (24-31): Plucky attack, bright tone, medium sustain - needs distinct synthesis from pads
Bass (32-39): Low-frequency fundamentals, sub-bass energy, short attack
Strings (40-47): Sustained bowing, rich harmonics, smooth legato
Brass (56-63): Bright attack, sustained tone, powerful projection
Reed/Woodwinds (64-79): Breathy attack, organic timbre, expressive dynamics
Synth Lead (80-87): Bright, cutting, aggressive - designed for melody
Synth Pad (88-95): Soft attack, long sustain, atmospheric - designed for background
Ethnic/Percussive (104-119): Plucky or struck sounds with unique timbres

Piano (0-7)

0: "Acoustic Grand Piano" 1: "Bright Acoustic Piano" 2: "Electric Grand Piano" 3: "Honky-tonk Piano" 4: "Electric Piano 1" 5: "Electric Piano 2" 6: "Harpsichord" 7: "Clavinet"

Chromatic Percussion (8-15)

8: "Celesta" 9: "Glockenspiel" 10: "Music Box" 11: "Vibraphone" 12: "Marimba" 13: "Xylophone" 14: "Tubular Bells" 15: "Dulcimer"

Organ (16-23)

16: "Drawbar Organ" 17: "Percussive Organ" 18: "Rock Organ" 19: "Church Organ" 20: "Reed Organ" 21: "Accordion" 22: "Harmonica" 23: "Tango Accordion"

Guitar (24-31)

24: "Acoustic Guitar (nylon)" 25: "Acoustic Guitar (steel)" 26: "Electric Guitar (jazz)" 27: "Electric Guitar (clean)" 28: "Electric Guitar (muted)" 29: "Overdriven Guitar" 30: "Distortion Guitar" 31: "Guitar Harmonics"

Bass (32-39)

32: "Acoustic Bass" 33: "Electric Bass (finger)" 34: "Electric Bass (pick)" 35: "Fretless Bass" 36: "Slap Bass 1" 37: "Slap Bass 2" 38: "Synth Bass 1" 39: "Synth Bass 2"

Strings (40-47)

40: "Violin" 41: "Viola" 42: "Cello" 43: "Contrabass" 44: "Tremolo Strings" 45: "Pizzicato Strings" 46: "Orchestral Harp" 47: "Timpani"

Ensemble (48-55)

48: "String Ensemble 1" 49: "String Ensemble 2" 50: "Synth Strings 1" 51: "Synth Strings 2" 52: "Choir Aahs" 53: "Voice Oohs" 54: "Synth Voice" 55: "Orchestra Hit"

Brass (56-63)

56: "Trumpet" 57: "Trombone" 58: "Tuba" 59: "Muted Trumpet" 60: "French Horn" 61: "Brass Section" 62: "Synth Brass 1" 63: "Synth Brass 2"

Reed (64-71)

64: "Soprano Sax" 65: "Alto Sax" 66: "Tenor Sax" 67: "Baritone Sax" 68: "Oboe" 69: "English Horn" 70: "Bassoon" 71: "Clarinet"

Pipe (72-79)

72: "Piccolo" 73: "Flute" 74: "Recorder" 75: "Pan Flute" 76: "Blown Bottle" 77: "Shakuhachi" 78: "Whistle" 79: "Ocarina"

Synth Lead (80-87)

80: "Lead 1 (square)" 81: "Lead 2 (sawtooth)" 82: "Lead 3 (calliope)" 83: "Lead 4 (chiff)" 84: "Lead 5 (charang)" 85: "Lead 6 (voice)" 86: "Lead 7 (fifths)" 87: "Lead 8 (bass + lead)"

Synth Pad (88-95)

88: "Pad 1 (new age)" 89: "Pad 2 (warm)" 90: "Pad 3 (polysynth)" 91: "Pad 4 (choir)" 92: "Pad 5 (bowed)" 93: "Pad 6 (metallic)" 94: "Pad 7 (halo)" 95: "Pad 8 (sweep)"

Synth Effects (96-103)

96: "FX 1 (rain)" 97: "FX 2 (soundtrack)" 98: "FX 3 (crystal)" 99: "FX 4 (atmosphere)" 100: "FX 5 (brightness)" 101: "FX 6 (goblins)" 102: "FX 7 (echoes)" 103: "FX 8 (sci-fi)"

Ethnic (104-111)

104: "Sitar" 105: "Banjo" 106: "Shamisen" 107: "Koto" 108: "Kalimba" 109: "Bag pipe" 110: "Fiddle" 111: "Shanai"

Percussive (112-119)

112: "Tinkle Bell" 113: "Agogo" 114: "Steel Drums" 115: "Woodblock" 116: "Taiko Drum" 117: "Melodic Tom" 118: "Synth Drum" 119: "Reverse Cymbal"

Sound Effects (120-127)

120: "Guitar Fret Noise" 121: "Breath Noise" 122: "Seashore" 123: "Bird Tweet" 124: "Telephone Ring" 125: "Helicopter" 126: "Applause" 127: "Gunshot"

Complete Drum Map (MIDI Channel 10, Notes 35-81)

Drums use note numbers for different sounds, NOT pitch. Must be on channel 10 (9 in 0-indexed).

Bass Drums

35: "Acoustic Bass Drum" 36: "Bass Drum 1" # Most common kick

Snares

38: "Acoustic Snare" # Standard snare 40: "Electric Snare"

Toms

41: "Low Floor Tom" 43: "High Floor Tom" 45: "Low Tom" 47: "Low-Mid Tom" 48: "Hi-Mid Tom" 50: "High Tom"

Hi-Hats

42: "Closed Hi-Hat" # Most used 44: "Pedal Hi-Hat" 46: "Open Hi-Hat"

Cymbals

49: "Crash Cymbal 1" 51: "Ride Cymbal 1" 52: "Chinese Cymbal" 53: "Ride Bell" 55: "Splash Cymbal" 57: "Crash Cymbal 2" 59: "Ride Cymbal 2"

Percussion

37: "Side Stick" 39: "Hand Clap" 54: "Tambourine" 56: "Cowbell" 58: "Vibraslap" 60: "Hi Bongo" 61: "Low Bongo" 62: "Mute Hi Conga" 63: "Open Hi Conga" 64: "Low Conga" 65: "High Timbale" 66: "Low Timbale" 67: "High Agogo" 68: "Low Agogo" 69: "Cabasa" 70: "Maracas" 71: "Short Whistle" 72: "Long Whistle" 73: "Short Guiro" 74: "Long Guiro" 75: "Claves" 76: "Hi Wood Block" 77: "Low Wood Block" 78: "Mute Cuica" 79: "Open Cuica" 80: "Mute Triangle" 81: "Open Triangle"

How to Use Any Instrument (mido workflow)

CRITICAL RULE: music21 does NOT reliably export program_change messages, even when using instrument classes like instrument.TenorSaxophone() or instrument.AcousticGuitar() . mido MUST ALWAYS be used to INSERT program_change messages manually after exporting to MIDI. Without this step, all tracks will sound like piano (program 0).

Common mistake: Assuming that sax_part.insert(0, instrument.TenorSaxophone()) will automatically make the track sound like a saxophone. It won't! mido must still be used to set the program number.

Helper Function for Setting Instruments:

from mido import Message

def set_track_instrument(track, program): """Insert a program_change message at the beginning of a MIDI track.""" # Find position after all meta messages (track_name, etc.) insert_pos = 0 for j, msg in enumerate(track): if not msg.is_meta: # Insert before first non-meta message insert_pos = j break else: # If all messages are meta, insert at end insert_pos = len(track) track.insert(insert_pos, Message('program_change', program=program, time=0))

Usage after loading MIDI with mido:

set_track_instrument(mid.tracks[2], 33) # Set track 2 to Electric Bass

Step 1: Compose with music21 (use placeholder or skip instrument)

from music21 import stream, note, chord, tempo

score = stream.Score()

Create parts - don't worry about instrument assignment yet

synth_lead = stream.Part() synth_pad = stream.Part() bass = stream.Part()

Add your notes/chords using .insert() with explicit timing

CRITICAL: Always use .insert(offset, note) not .append(note)

offset = 0.0 synth_lead.insert(offset, note.Note('E5', quarterLength=1.0)) offset += 1.0 synth_lead.insert(offset, note.Note('G5', quarterLength=1.0))

... compose your music with .insert()

score.append(synth_lead) score.append(synth_pad) score.append(bass)

Export to MIDI

midi_path = # define a output path score.write('midi', fp=midi_path)

Step 2: Inspect MIDI structure and assign instruments with mido

from mido import MidiFile, Message

mid = MidiFile(midi_path)

CRITICAL: DO NOT assume track numbers! Inspect the MIDI file first.

Print track structure to see what tracks exist

print(f"Total tracks: {len(mid.tracks)}") for i, track in enumerate(mid.tracks): note_count = sum(1 for msg in track if msg.type == 'note_on' and msg.velocity > 0) print(f"Track {i}: {note_count} notes")

Helper function to set instruments

def set_track_instrument(track, program): """Insert a program_change message at the beginning of a MIDI track.""" insert_pos = 0 for j, msg in enumerate(track): if not msg.is_meta: insert_pos = j break else: insert_pos = len(track) track.insert(insert_pos, Message('program_change', program=program, time=0))

Based on inspection, assign instruments to the correct tracks

Example: if [drums, bass, guitar] were appended and inspection shows tracks 1, 2, 3 have notes:

set_track_instrument(mid.tracks[1], 80) # First part - Square Lead set_track_instrument(mid.tracks[2], 88) # Second part - Pad set_track_instrument(mid.tracks[3], 38) # Third part - Bass

mid.save(midi_path)

Step 3: For drums, ALSO set channel to 9 (channel 10)

If track is drums, set ALL messages to channel 9

for i, track in enumerate(mid.tracks): if i == 1: # This is the drum track for msg in track: if hasattr(msg, 'channel'): msg.channel = 9 # Channel 10 in 1-indexed

Step 4: Render to audio

from midi2audio import FluidSynth from pydub import AudioSegment

fs = FluidSynth('/usr/share/sounds/sf2/FluidR3_GM.sf2') wav_path = # define a path here fs.midi_to_audio(midi_path, wav_path)

audio = AudioSegment.from_wav(wav_path) mp3_path = # define a path here audio.export(mp3_path, format='mp3', bitrate='192k')

Common Chord Progressions & Styles

Standard Progressions (Roman numerals)

"pop": ["I", "V", "vi", "IV"] # C-G-Am-F (Journey, Adele) "epic": ["i", "VI", "III", "VII"] # Am-F-C-G (Epic trailer music) "sad": ["i", "VI", "iv", "V"] # Am-F-Dm-E (Melancholic) "jazz": ["ii", "V", "I", "vi"] # Dm-G-C-Am (Jazz standard) "classical": ["I", "IV", "V", "I"] # C-F-G-C (Classical cadence) "blues": ["I", "I", "I", "I", "IV", "IV", "I", "I", "V", "IV", "I", "I"] # 12-bar blues "house": ["i", "VI", "III", "VII"] # Minor house progression "reggae": ["I", "V", "vi", "IV"] # Offbeat rhythm style "country": ["I", "IV", "V", "I"] # Simple and direct "rock": ["I", "bVII", "IV", "I"] # Power chord style "r&b": ["I", "V", "vi", "iii", "IV", "I", "IV", "V"] # Complex R&B

Genre-Specific Characteristics

STYLES = { "house": { "bpm": 120-128, "time_signature": "4/4", "drum_pattern": "4-on-floor kick, offbeat hats", "bass": "Synth bass with groove", "common_instruments": [38, 80, 88, 4] # Synth bass, lead, pad, e-piano }, "jazz": { "bpm": 100-180, "time_signature": "4/4 or 3/4", "chords": "Extended (7th, 9th, 11th, 13th)", "common_instruments": [0, 32, 64, 56, 73] # Piano, bass, sax, trumpet, drums }, "orchestral": { "bpm": 60-140, "sections": ["strings", "woodwinds", "brass", "percussion"], "common_instruments": [40, 41, 42, 56, 73, 47] # Violin, viola, cello, trumpet, flute, timpani }, "rock": { "bpm": 100-140, "time_signature": "4/4", "guitars": "Distorted (30) or clean (27)", "common_instruments": [30, 33, 0, 128] # Distortion guitar, bass, piano, drums }, "ambient": { "bpm": 60-90, "characteristics": "Long sustained notes, atmospheric pads", "common_instruments": [88, 89, 90, 91, 52] # Various pads, choir }, "trap": { "bpm": 130-170, "drums": "Tight snare rolls, 808 bass kicks", "hi_hats": "Fast hi-hat patterns (1/16 or 1/32 notes)", "common_instruments": [38, 128] # Synth bass, drums } }

music21 Instrument Classes

from music21 import instrument

Strings

instrument.Violin() instrument.Viola() instrument.Violoncello() # Note: NOT Cello() instrument.Contrabass() instrument.Harp()

Piano

instrument.Piano() instrument.Harpsichord()

Brass

instrument.Trumpet() instrument.Trombone() instrument.Tuba() instrument.Horn() # French horn

Woodwinds

instrument.Flute() instrument.Clarinet() instrument.Oboe() instrument.Bassoon() instrument.SopranoSaxophone() instrument.AltoSaxophone() instrument.TenorSaxophone() # Most common for jazz instrument.BaritoneSaxophone()

Other

instrument.AcousticGuitar() instrument.ElectricGuitar() instrument.Bass() instrument.Timpani()

CRITICAL: music21 has LIMITED support for electronic instruments and drums

For synths, drums, and electronic sounds, the following steps must be taken:

1. Create a Part without an instrument (or use a placeholder like Piano())

2. Use mido library to INSERT program_change messages after export

3. Set drums to MIDI channel 10 (channel 9 in 0-indexed) or they won't sound like drums

Common mistakes:

- instrument.Cello() doesn't exist - use Violoncello()

- instrument.FrenchHorn() doesn't exist - use Horn()

- Setting part.partName doesn't change the sound - MIDI program must be set with mido

- Drums on channel 0 will play as pitched notes, not drum sounds

Note Durations (Quarter Note = 1.0)

Whole note: 4.0
Half note: 2.0
Quarter note: 1.0
Eighth note: 0.5
Sixteenth note: 0.25
Dotted quarter: 1.5
Triplet quarter: 0.667

mido Quick Reference

For electronic music and drums, use mido to set MIDI programs after music21 export:

from mido import MidiFile, Message

mid = MidiFile(midi_path)

Define helper function

Insert program_change messages

for i, track in enumerate(mid.tracks): if i == 1: # Your track (tracks start at 1, not 0) set_track_instrument(track, 38) # Synth Bass 1

For drums: Set channel to 9 (channel 10 in 1-indexed)

for i, track in enumerate(mid.tracks): if i == 1: # Drum track for msg in track: if hasattr(msg, 'channel'): msg.channel = 9

mid.save(midi_path)

Common MIDI Programs:

38: Synth Bass 1
80: Square Lead
81: Sawtooth Lead
88: Pad 1 (New Age)
25: Acoustic Guitar (Steel) - loud, cuts through
33: Acoustic Bass

Common Techniques

Drum Programming (4-on-floor house beat)

CRITICAL: music21's .append() adds notes sequentially (one after another), not simultaneously. For layered drums where kicks, snares, and hats play at the same time, .insert(offset, note) MUST be used with explicit timing.

ALWAYS USE .insert() FOR ADDING NOTES TO PARTS:

Since layering is needed for nearly all good music composition, part.insert(offset, note) MUST ALWAYS be used for ALL tracks - drums, bass, guitar, pads, everything. This prevents timing bugs and ensures proper synchronization.

NEVER mix .insert() and .append() when adding notes to parts - If .insert() is used for drums and .append() for other instruments, music21 will miscalculate track lengths and create tracks that are 5-10× longer than intended (8 minutes instead of 1.5 minutes), with only the first 20-25% containing actual sound.

Note: Using score.append(part) to add Parts to the Score is fine - the issue is specifically about adding notes/chords to Parts, not adding Parts to Scores.

Correct Pattern:

RIGHT: Use .insert() for notes, .append() for parts

drum_part = stream.Part() bass_part = stream.Part()

offset = 0.0 for beat in range(16): # Kick and hi-hat on same beat (layered) drum_part.insert(offset, note.Note(36, quarterLength=0.5)) # Kick drum_part.insert(offset, note.Note(42, quarterLength=0.5)) # Hi-hat

# Bass note
bass_part.insert(offset, note.Note('A2', quarterLength=0.5))

offset += 0.5  # Advance time

Add parts to score (this .append() is fine)

score.append(drum_part) score.append(bass_part)

Ensuring Complete Bar Coverage

CRITICAL: When composing with loops, ensure your notes completely fill each bar without gaps. A common mistake is placing notes that don't span the full bar duration, leaving silent gaps.

Problem Pattern (creates gaps):

bar_length = 1.5 # 6/8 time signature offset = 0.0

for bar in range(8): # Only fills first 1.0 quarter lengths, leaving 0.5 silent! guitar_part.insert(offset, note.Note('D3', quarterLength=0.5)) guitar_part.insert(offset + 0.5, chord.Chord(['D3', 'F#3', 'A3'], quarterLength=0.5)) # Missing: offset + 1.0 to offset + 1.5

offset += bar_length  # Advances to next bar, but gap remains

Result: Guitar plays for 10 seconds, then silence for remaining duration

Solution Pattern (complete coverage):

bar_length = 1.5 # 6/8 time signature offset = 0.0

for bar in range(8): # Fill the ENTIRE bar with notes guitar_part.insert(offset, note.Note('D3', quarterLength=0.5)) # 0.0 to 0.5 guitar_part.insert(offset + 0.5, chord.Chord(['D3', 'F#3', 'A3'], quarterLength=0.5)) # 0.5 to 1.0 guitar_part.insert(offset + 1.0, note.Note('D3', quarterLength=0.5)) # 1.0 to 1.5 ✓ Complete!

offset += bar_length

Result: Guitar plays continuously throughout the entire piece

Best Practice: Before advancing offset += bar_length , verify that your last note ends exactly at offset + bar_length . For example:

If bar_length = 1.5 , your last note should start at offset + 1.0 with quarterLength=0.5 to reach offset + 1.5
If bar_length = 2.0 , your last note should start at offset + 1.5 with quarterLength=0.5 to reach offset + 2.0

Best Practices

Composition Quality

Generate variety: Don't repeat the same 4 bars for entire piece
Use music theory: Real chord progressions, proper voice leading
Respect instrument ranges: Violin (G3-E7), Cello (C2-C6), Trumpet (E3-C6)
Add dynamics: Use p, mp, mf, f, ff markings and crescendos
Structure: Intro → Development → Climax → Resolution
Add humanization: Vary timing and velocity to avoid robotic sound import random n = note.Note('C5', quarterLength=1.0 + random.uniform(-0.05, 0.05)) n.volume.velocity = 80 + random.randint(-5, 5)

Technical Quality

SoundFont: Use FluidR3_GM.sf2 for best quality
Bitrate: 192kbps minimum, 320kbps for high quality
Limiting: Applied via audio.compress_dynamic_range() to prevent clipping
Timing precision: Use quarterLength values carefully
Cleanup: Remove temporary MIDI/WAV files after MP3 conversion

Common Pitfalls

CRITICAL: NEVER assume track numbers - DO NOT blindly use if i == 3 for guitar. ALWAYS inspect the MIDI file first with note counts to verify which track is which
CRITICAL: Always use part.insert(offset, note) for adding notes to parts - Never use part.append(note) or mix .insert() and .append() . This causes timing bugs where tracks are 5-10x longer than intended with only 20-25% containing sound. See "Drum Programming" section for details
CRITICAL: INSERT program_change messages - Use track.insert(pos, Message('program_change', ...)) not msg.program = X . See mido Quick Reference
CRITICAL: Set velocities - Lead 90-105, background 50-65. See "Mixing and Balance" section
CRITICAL: Bass octaves - Use A1-A2 (55-110 Hz), never A0-G0 (inaudible on most systems)
instrument.Cello() doesn't exist - use Violoncello()
Forgetting tempo - Add tempo.MetronomeMark() to first part
Drums not sounding like drums - Set channel to 9 with mido (see mido Quick Reference)

Mixing and Balance

CRITICAL: Setting MIDI program numbers alone is not enough. Without explicit velocity control, some instruments will be completely inaudible.

Setting Velocities

music21 uses default velocity 64 for all notes, which causes poor mixing. Use mido to set velocities after MIDI export:

from mido import MidiFile

def set_track_velocity(track, velocity): """Set velocity for all note_on messages in a track.""" for msg in track: if msg.type == 'note_on' and msg.velocity > 0: msg.velocity = velocity

mid = MidiFile(midi_path) for i, track in enumerate(mid.tracks): if i == 1: # Drums set_track_velocity(track, 75) elif i == 2: # Bass set_track_velocity(track, 80) elif i == 3: # Lead instrument (sax, guitar, trumpet) set_track_velocity(track, 95) elif i == 4: # Background (organ, pads) set_track_velocity(track, 55) mid.save(midi_path)

Velocity Guidelines

By Role:

Lead instruments (melody, solos): 90-105
Rhythm instruments (guitar skanks, comping): 85-100
Bass: 75-85
Drums: 70-90
Background (pads, organs): 50-65

By Frequency Range:

Low (20-250 Hz): Bass, kick - only ONE dominant at 75-85
Mid (250-2000 Hz): Most crowded - use velocity to separate (lead 90+, background 50-65)
High (2000+ Hz): Hi-hats, cymbals - 70-85 for clarity without harshness

Soundfont Level Issues

FluidR3_GM instruments are recorded at different levels. Even with correct velocities, some instruments may be inaudible:

Quiet programs (avoid for lead/rhythm):

Program 27 (Electric Guitar - clean) - Very quiet
Program 24 (Acoustic Guitar - nylon)
Program 73 (Flute)

Better alternatives:

Program 25 (Acoustic Guitar - steel) - 8-10dB louder, cuts through
Program 28 (Electric Guitar - muted) - Percussive
Program 30 (Distortion Guitar) - Aggressive

Additional fixes:

Increase note duration (0.4 quarterLength minimum vs 0.25)
Use octave separation (move competing instruments to different octaves)
Extreme velocity contrast (quiet instrument at 110, loud at 40)

Mixing Checklist

Before rendering:

✅ Lead at velocity 90-105
✅ Background at velocity 50-65
✅ Bass at velocity 75-85
✅ Check for quiet instruments (programs 24, 27, 73) and use alternatives
✅ Minimum 0.4 quarterLength for rhythm instruments

Resources

music21 Documentation: https://web.mit.edu/music21/doc/
General MIDI Spec: https://www.midi.org/specifications-old/item/gm-level-1-sound-set
Music Theory: https://www.musictheory.net/
IMSLP (Free Scores): https://imslp.org/ - Download classical MIDIs here!

Limitations

Instrumental only - No lyrics/vocals
MIDI-based synthesis - Not studio-quality recordings
No real-time playback - Files must be rendered before playback