accompy 🎵

Generate backing track audio from chord charts in Python — like iReal Pro, but scriptable.

from accompy import generate_accompaniment

# Generate a bossa nova backing track
audio = generate_accompaniment("| Dm7 | G7 | C^7 | A7b9 |", style="bossa", tempo=140)
print(f"Generated: {audio}")  # -> /tmp/xxx.wav

Features

• Simple API: One function to generate complete backing tracks
• Multiple styles: Swing, bossa nova, rock, funk, ballad, latin, waltz, blues
• Flexible chord inputs: Strings, Score, iReal URLs, or (chord, beats) tuples
• Backend selector: backend="auto"|"mma"|"builtin" (with backwards-compatible use_mma)
• iReal Pro compatible: Parse iReal Pro URLs directly (with optional pyRealParser)
• Multi-instrument: Drums, bass, piano with style-appropriate patterns
• Audio output: WAV, MP3, FLAC via FluidSynth
• MIDI output: Save .mid directly (skip audio rendering)
• Extensible: Add custom patterns and styles

Quick Start

Installation

pip install accompy

# Or install from source:
git clone https://github.com/thorwhalen/accompy
pip install -e accompy

System Dependencies

accompy requires FluidSynth and a SoundFont for audio rendering.

Automated Setup (Recommended)

The easiest way to get started:

# Install accompy
pip install -e .

# Run automated setup (interactive)
python -c "from accompy import verify_and_setup; verify_and_setup()"

# This will:
# - Check all dependencies
# - Offer to install missing ones (with your permission)
# - Download and configure SoundFont files
# - Verify everything works

Manual Setup

If you prefer to install manually:

# macOS
brew install fluid-synth

# Ubuntu/Debian
sudo apt-get install fluidsynth fluid-soundfont-gm

# Install Python dependencies
pip install midiutil mingus

# Verify setup
python -m accompy --check-deps

SoundFont (important for sound quality!)

FluidSynth renders MIDI using SoundFont sample banks (.sf2 files). The SoundFont determines the quality of every instrument you hear. FluidSynth's bundled SoundFont (VintageDreamsWaves-v2.sf2, ~300 KB) is a bare-minimum placeholder made of basic waveforms — it will sound terrible.

For good results, install a full General MIDI SoundFont with real instrument samples:

mkdir -p ~/.fluidsynth

# MuseScore General (~200 MB, MIT license, good all-around quality)
curl -L -o ~/.fluidsynth/default_sound_font.sf2 \
  "https://ftp.osuosl.org/pub/musescore/soundfont/MuseScore_General/MuseScore_General.sf2"

Other recommended SoundFonts:

• GeneralUser GS (~30 MB) — excellent bass and drums, free for commercial use. Download from https://schristiancollins.com/generaluser.php
• FluidR3_GM (~140 MB) — the classic GM SoundFont, widely used.

Browse more at https://musical-artifacts.com/artifacts?formats=sf2.

After downloading, place or symlink the file at ~/.fluidsynth/default_sound_font.sf2 (accompy looks there by default).

Check Your Setup

# Quick check
python -c "from accompy import check_dependencies; print(check_dependencies())"

# Detailed diagnostic report
python -c "from accompy import print_diagnostic_report; print_diagnostic_report()"

Usage

Basic Usage

from accompy import generate_accompaniment

# Generate with default settings
audio = generate_accompaniment("| C | Am | F | G |")

# Specify style and tempo
audio = generate_accompaniment(
    "| Dm7 | G7 | Cmaj7 | Am7 |",
    style="swing",
    tempo=160,
    repeats=4,
    output_path="my_track.wav",
)

# Generate MIDI only (skip audio rendering)
midi = generate_accompaniment(
    "| Dm7 | G7 | Cmaj7 | Am7 |",
    output_path="my_track.mid",
)

Using Score Objects

For more control, create a Score object:

from accompy import Score, generate_accompaniment

# Parse chord string
score = Score.from_string(
    "| Dm7 | G7 | Cmaj7 | % |",  # % = repeat previous chord
    title="ii-V-I in C",
    key="C",
    time_signature=(4, 4)
)

# Generate audio
audio = generate_accompaniment(score, style="swing", tempo=120)

### Flexible Chord Inputs

`generate_accompaniment(...)` accepts several common chord progression formats.

```python
from accompy import ensure_score, generate_accompaniment

# 1) iReal-style chord strings
generate_accompaniment("| C | Am | F | G |")

# 2) iReal Pro URL strings (irealbook://... or irealb://...)
generate_accompaniment("irealbook://Autumn%20Leaves=...")

# 3) List of (chord, beats) tuples (like `accompany`)
chords = [("F#m7b5", 4), ("B7", 4), ("Em", 8)]
score = ensure_score(chords, key="E")
generate_accompaniment(score)

Backend Selection

Choose which generator to use:

from accompy import generate_accompaniment

# Auto: use MMA if available, else builtin
generate_accompaniment("| Dm7 | G7 | Cmaj7 | Am7 |", backend="auto")

# Force builtin generator
generate_accompaniment("| Dm7 | G7 | Cmaj7 | Am7 |", backend="builtin")

# Force MMA (errors if MMA isn't installed)
generate_accompaniment("| Dm7 | G7 | Cmaj7 | Am7 |", backend="mma")

### Chord Notation

accompy supports flexible chord notation:

```python
# Jazz notation (iReal Pro style)
"| C^7 | D-7 | G7 | C^7 |"   # ^7=maj7, -7=min7

# Standard notation  
"| Cmaj7 | Dm7 | G7 | Cmaj7 |"

# Simple notation
"| C | Dm | G | C |"

# Multiple chords per bar
"| Dm7 G7 | Cmaj7 |"  # Two chords, split evenly

# Repeat symbols
"| C | G | % | F |"   # % repeats G

Chord symbol reference:

Notation	Meaning
C, Cmaj	C major
C-, Cm, Cmin	C minor
C7	C dominant 7
C^7, Cmaj7	C major 7
C-7, Cm7, Cmin7	C minor 7
Co, Cdim	C diminished
Co7, Cdim7	C diminished 7
Ch7, Cm7b5	C half-diminished
C+, Caug	C augmented
Csus, Csus4	C suspended 4th

Styles

Available styles with characteristic patterns:

Style	Description	Typical Tempo
swing	Jazz swing with walking bass	120-200 BPM
bossa	Bossa nova with syncopated feel	100-150 BPM
rock	Straight 8ths rock beat	100-140 BPM
funk	Syncopated funk groove	90-120 BPM
ballad	Slow, sustained ballad	60-90 BPM
latin	Latin/salsa with clave	100-130 BPM
waltz	3/4 waltz pattern	90-150 BPM
blues	Blues shuffle	80-120 BPM

iReal Pro Integration

Parse and play iReal Pro chord charts:

from accompy import Score, generate_accompaniment

# From iReal Pro URL (copy from app or forum)
url = "irealb://6dim=Composer%20Unknown==Medium%20Swing=C=7=1r34LbKcu7QyX%2DA6XyQ%7C%23G%7CQyXG%2F6C%7CQyXFo%7CQyXE%2F6C%7CQyXoDoXyQ%7CC44T%7BXQyXQQ%7DXyQQyXQyXQyXQyXQyQXyXQyXQyXQyXQyXXyQXyyXoB%7CQyXQyXyQXyyXQyXQyXQyXQyXyQXQyXQyXQyXQyXQQXyQXQyXQyyXQyXQXyQXXQyXQyXQyXQyXQXyQyXQyXQyXQyXQyyQXyQyXQyXQXyQXyQXyQXyQXyQ%20Z%20=Jazz%2DMedium%20Up%20Swing%202=118=21]6dim"
score = Score.from_ireal_url(url)

# Generate backing track
audio = generate_accompaniment(score, style="swing", tempo=140)

Note: pyRealParser is optional. If installed, Score.from_ireal_url(...) will use it. If not installed, accompy uses a best-effort built-in parser.

Advanced Configuration

Full control with AccompanimentConfig:

from accompy import AccompanimentConfig, generate_accompaniment

config = AccompanimentConfig(
    style="swing",
    tempo=160,
    repeats=4,
    instruments={
        "drums": True,
        "bass": True,
        "piano": True,
        "guitar": False,
    },
    volumes={
        "drums": 0.7,
        "bass": 1.0,
        "piano": 0.6,
    },
    sample_rate=44100,
    output_format="mp3",  # wav, mp3, flac, midi
)

audio = generate_accompaniment(
    "| Dm7 | G7 | Cmaj7 | A7 |", config=config, output_path="backing_track.mp3"
)

Rhythmic Skeletons

For simple chord renderings (no drums or bass — just restriking chords with a rhythmic feel), use rhythm_to_midi or rhythm_to_audio:

from accompy import rhythm_to_midi, rhythm_to_audio

# Tresillo feel (1.5 + 1.5 + 1 beats)
midi = rhythm_to_midi("| Dm7 | G7 | Cmaj7 |", skeleton="tresillo", tempo=120)
midi.write("tresillo.mid")

# Whole notes (one strike per measure) — the default
midi = rhythm_to_midi("| C | Am | F | G |")

# Charleston, bossa, waltz, and 25+ other built-in skeletons
midi = rhythm_to_midi("| C | Am | F | G |", skeleton="charleston")

# Or pass a raw duration tuple
midi = rhythm_to_midi("| C | Am |", skeleton=(1.5, 0.5, 1.5, 0.5))

# Render all the way to audio
audio = rhythm_to_audio("| C | Am |", skeleton="half_notes", tempo=100)

A rhythmic skeleton is just a tuple of durations that sum to the measure length — e.g. (1.5, 1.5, 1) says "hit, hold for a dotted quarter; hit again, hold for another dotted quarter; hit once more, hold for a quarter." No pitches, no voicings, no velocities. The skeleton defines when you strike within a measure; the chord progression defines what you play.

from accompy import resolve_skeleton, list_skeletons, register_skeleton

# Resolve by key, name, or style
resolve_skeleton("tresillo")  # (1.5, 1.5, 1)
resolve_skeleton("Dotted half + quarter")  # (3, 1)
resolve_skeleton("reggae")  # picks first skeleton for that style

# List available skeletons
list_skeletons()  # all keys
list_skeletons(beats_per_measure=3)  # waltz-family only
list_skeletons(style="jazz")  # jazz-associated skeletons

# Register your own
register_skeleton("my_groove", (1, 0.5, 0.5, 2), name="My Groove", styles=["custom"])

Extensibility & Custom Patterns

New in v0.2.0: accompy now supports extensive customization through a protocol-based architecture.

Custom Chord Voicings

Provide your own chord-to-notes resolver:

from accompy import set_chord_resolver, generate_accompaniment


def jazz_voicing_resolver(symbol: str) -> list[int]:
    """Custom jazz voicings with rootless chords, tensions, etc."""
    # Your custom chord resolution logic
    # Return list of MIDI note numbers
    return [55, 59, 62, 65, 69]  # Example: Dm9 voicing


# Set as default resolver
set_chord_resolver(jazz_voicing_resolver)

# Now all accompaniments use your custom voicings
audio = generate_accompaniment("| Dm7 | G7 | Cmaj7 |")

Custom Patterns

Register your own accompaniment patterns:

from accompy import (
    register_style,
    DrumPattern,
    BassPattern,
    DrumHit,
    NoteEvent,
    KICK,
    SNARE,
    CLOSED_HIHAT,
)

# Define custom drum pattern
my_drum = DrumPattern(
    name="my_funk",
    beats_per_bar=4,
    hits=[
        DrumHit(0, KICK, 110),
        DrumHit(0.75, KICK, 85),
        DrumHit(1, SNARE, 105),
        DrumHit(2, KICK, 110),
        DrumHit(3, SNARE, 105),
        # ... more hits
    ],
)

# Define custom bass pattern
my_bass = BassPattern(
    name="my_funk",
    notes=[
        NoteEvent(0, 0, 0.4, 110),  # Root, short
        NoteEvent(0.75, 0, 0.2, 80),  # Root, ghostNote
        NoteEvent(1.5, 7, 0.3, 90),  # 5th
        # ... more notes
    ],
)

# Register the custom style
register_style("my_funk", drums=[my_drum], bass=[my_bass], comp=[])

# Use it
audio = generate_accompaniment("| C7 | F7 | C7 | G7 |", style="my_funk")

Pattern Registry

The pattern registry is a MutableMapping, making it Pythonic and extensible:

from accompy import get_pattern_registry

registry = get_pattern_registry()

# Check available styles
print(registry.available_styles())  # ['swing', 'bossa', 'rock', ...]

# Access patterns like a dict
swing_patterns = registry["swing"]
print(swing_patterns["drums"])  # List of DrumPattern objects

# Add/modify styles at runtime
registry["custom_groove"] = {
    "drums": [custom_drum_pattern],
    "bass": [custom_bass_pattern],
    "comp": [custom_comp_pattern],
}

Real-Time Event Generation

For advanced use cases (future integration with hum/pyo for real-time synthesis):

from accompy import RealtimeAccompaniment, AccompanimentConfig

# Create real-time player
config = AccompanimentConfig(tempo=120, style="swing")
player = RealtimeAccompaniment(config)

# Set chord progression
player.set_chords("| Dm7 | G7 | Cmaj7 | A7 |")

# Get event iterator (for future real-time playback)
for event in player.events():
    # event.time, event.note, event.velocity, event.duration
    # Future: send to real-time synth like hum/pyo
    pass

Protocol-Based Architecture

All major components implement protocols for maximum flexibility:

from accompy.protocols import ChordResolver, PatternSource, SynthesizerBackend

# Implement custom components that satisfy these protocols
# See accompy/protocols.py for full definitions


# Example: Custom synthesis backend
class MySynthBackend(SynthesizerBackend):
    def render_to_file(self, midi_path, output_path, *, sample_rate=44100):
        # Your custom synthesis logic (e.g., using hum, pyo, etc.)
        pass

    @classmethod
    def is_available(cls):
        return True  # Check if dependencies are available


# Use with dependency injection
from accompy import AccompanimentConfig, generate_accompaniment

config = AccompanimentConfig(synthesis_backend=MySynthBackend())
audio = generate_accompaniment("| C | G | Am | F |", config=config)

Command Line

# Generate backing track
python -m accompy "| C | Am | F | G |" -s bossa -t 120 -o track.wav

# Check dependencies
python -m accompy --check-deps

# Options
python -m accompy --help

How It Works

1. Parse chords: Convert chord string → Score object with normalized chord symbols
2. Generate MIDI: Create multi-track MIDI with drums, bass, piano patterns
   • Uses MMA (Musical MIDI Accompaniment) if available for realistic tracks
   • Falls back to built-in pattern generator
3. Render audio: Convert MIDI → WAV using FluidSynth with SoundFont
4. Convert format: Optionally convert to MP3/FLAC via ffmpeg or pydub

MMA (Musical MIDI Accompaniment)

For the best quality backing tracks, install MMA:

# MMA provides 50+ professionally designed grooves
git clone https://github.com/infojunkie/mma
cd mma && python install  # Follow MMA installation instructions

MMA offers extensive groove libraries with realistic fills, variations, and transitions.

Python Dependencies

Required:

• midiutil — MIDI file generation

Recommended:

• mingus — Music theory (better chord parsing)
• pyRealParser — iReal Pro URL parsing
• midi2audio — Optional Python wrapper for FluidSynth (can improve portability)
• pydub — Audio format conversion (if no ffmpeg)

pip install midiutil mingus pyRealParser midi2audio pydub

API Reference

generate_accompaniment(chords, *, style, tempo, repeats, output_path, output_format, config, use_mma, backend)

Generate accompaniment audio from chord progression.

Parameters:

• chords (str | Score | Iterable[tuple[str, int|float]] | Iterable[str] | list[list[str]]): Chord progression
• style (str): "swing", "bossa", "rock", "ballad", "funk", "latin", "waltz", "blues"
• tempo (int): BPM (default: 120)
• repeats (int): Number of times through the form (default: 2)
• output_path (str | Path): Where to save audio (default: temp file)
• output_format (str | None): "wav", "mp3", "flac", "midi" (optional; inferred from output_path)
• config (AccompanimentConfig): Full config (overrides style/tempo/repeats)
• use_mma (bool): Backwards-compatible MMA toggle (default: True)
• backend (str | None): "auto", "mma", "builtin" (optional)

Returns: Path to generated audio file

Score.from_string(chord_string, *, title, key, time_signature)

Parse chord string into Score object.

Score.from_ireal_url(url)

Parse iReal Pro URL into Score object.

check_dependencies()

Returns dict of available dependencies.

print_setup_instructions()

Print installation instructions for missing dependencies.

Troubleshooting

It sounds awful!

Problem: The generated audio plays but sounds robotic, hollow, or like cheap ringtones from 2003.

Cause: You're using a tiny placeholder SoundFont. FluidSynth ships with VintageDreamsWaves-v2.sf2 (~300 KB), which is made of basic sine waves — not real instrument samples. This is the #1 reason accompy output sounds bad.

How to check:

ls -lh ~/.fluidsynth/default_sound_font.sf2
# If it's under 1 MB, that's your problem.

Fix — install a real SoundFont:

# Download MuseScore General (~200 MB, real sampled instruments)
curl -L -o ~/.fluidsynth/default_sound_font.sf2 \
  "https://ftp.osuosl.org/pub/musescore/soundfont/MuseScore_General/MuseScore_General.sf2"

A proper SoundFont should be 30–200+ MB. See the SoundFont section above for more options, or browse https://musical-artifacts.com/artifacts?formats=sf2.

Tip: If you're using an AI coding agent (Claude Code, Cursor, etc.), just tell it: "the accompy output sounds bad, find and install a good SoundFont" — it can diagnose and fix this in seconds.

Common Issues

"No SoundFont found" Error

Problem: RuntimeError: No SoundFont found. Download FluidR3_GM.sf2 and place in ~/.fluidsynth/default_sound_font.sf2

Solutions:

1. Automated fix:

   python -c "from accompy import setup_soundfont; setup_soundfont()"
   

2. Check if FluidSynth includes a SoundFont:

   # macOS with Homebrew
   find /opt/homebrew/Cellar/fluid-synth -name "*.sf2"
   

   If found, run the automated setup to link it.

3. Manual download:

   mkdir -p ~/.fluidsynth
   # Download MuseScore General (high quality, 35MB)
   curl -L -o ~/.fluidsynth/default_sound_font.sf2 \
     "https://ftp.osuosl.org/pub/musescore/soundfont/MuseScore_General/MuseScore_General.sf2"
   

4. Verify the file:

   ls -lh ~/.fluidsynth/default_sound_font.sf2
   # Should be several MB (not just a few bytes)
   

"FluidSynth not found" Error

Problem: RuntimeError: FluidSynth not found. Install with: brew install fluidsynth

Solutions:

1. macOS:

   brew install fluid-synth
   

2. Ubuntu/Debian:

   sudo apt-get update
   sudo apt-get install fluidsynth
   

3. Windows: Download from FluidSynth releases and add to PATH

4. Verify installation:

   which fluidsynth
   fluidsynth --version
   

SoundFont File is Corrupted (255 bytes)

Problem: Downloaded SoundFont is tiny (255 bytes) and appears to be XML

Cause: Download URL redirected to an error page

Solution:

# Remove corrupted file
rm ~/.fluidsynth/default_sound_font.sf2

# Use automated setup
python -c "from accompy import setup_soundfont; setup_soundfont(force=True)"

# Or manually download from a reliable source
curl -L -o ~/.fluidsynth/default_sound_font.sf2 \
  "https://ftp.osuosl.org/pub/musescore/soundfont/MuseScore_General/MuseScore_General.sf2"

Import Warning About Missing Dependencies

Problem: Warning on import: accompy setup incomplete - missing: fluidsynth, soundfont

Solutions:

1. Run setup:

   python -c "from accompy import verify_and_setup; verify_and_setup()"
   

2. Temporarily disable warning:

   export ACCOMPY_SKIP_SETUP_CHECK=1
   python your_script.py
   

3. Fix manually and verify:

   # Install dependencies
   brew install fluid-synth  # or apt-get install fluidsynth
   pip install midiutil
   
   # Run diagnostic
   python -c "from accompy import print_diagnostic_report; print_diagnostic_report()"
   

"midiutil not found" Error

Problem: Missing Python dependency

Solution:

pip install midiutil mingus

Diagnostic Tools

Run Full Diagnostic

Get a comprehensive report of your setup:

from accompy import print_diagnostic_report

print_diagnostic_report()

This shows:

• System information
• Dependency status (✓ or ✗)
• Specific issues found
• Solutions for each issue

Check Specific Issues

from accompy import diagnose_issues

for issue, description, solution in diagnose_issues():
    print(f"Issue: {issue}")
    print(f"Description: {description}")
    print(f"Solution: {solution}\n")

Verify Individual Dependencies

from accompy import check_dependencies

deps = check_dependencies()
print(f"FluidSynth: {deps['fluidsynth']}")
print(f"SoundFont: {deps['soundfont']}")
print(f"midiutil: {deps['midiutil']}")
print(f"mingus: {deps['mingus']}")
print(f"MMA: {deps['mma']}")

Getting Help

If you're still having issues:

1. Run diagnostic report and save output:

   python -c "from accompy import print_diagnostic_report; print_diagnostic_report()" > diagnostic.txt
   

2. Check existing issues: GitHub Issues

3. Create a new issue with:

   • Your diagnostic report
   • What you tried
   • Full error message

Contributing

Contributions welcome! Areas of interest:

• Additional styles/grooves
• Better drum fills and variations
• Improved chord voicings
• More instrument parts (guitar, strings, horns)
• Web interface
• Better cross-platform setup automation

AI agent skills

Two skills ship with this repository. Their real files live in skills/, with a relative symlink per skill in .claude/skills/ so Claude Code finds them too — gh skill discovers non-hidden skills/ directories and skips hidden ones, so one location plus a symlink serves both.

Skill	What it covers
accompy-patterns	The conventions this codebase follows
user-data-folder	Where an app's user data lives (XDG paths, config2py.AppData, seeding from package data)

gh skill install thorwhalen/accompy user-data-folder

License

MIT

Acknowledgments

• MMA - Musical MIDI Accompaniment by Bob van der Poel
• FluidSynth team
• pyRealParser for iReal Pro format parsing
• iReal Pro for inspiration