ChopShop

A sample chopper for GarageBand. Load a breakbeat, slice it into individual hits, and play each one from a keyboard key.

Why

I wanted to make jungle and drum & bass in GarageBand but was disappointed in the painfully slow workflow of chopping a breakbeat. ChopShop takes an audio loop, slices it up, and generates an .aupreset file that GarageBand's AUSampler instrument can load directly. There is automatic hit detection and classification that is not great and can be tweaked by hand, it takes seconds to chop a sample and obtain an instrument in GarageBand that can be played! There is a CLI and a GUI.

Please be warned that this was vibecoded for personal use and is made public merely out of interest. There also may be a better way to chop samples and this project could be completely useless.

How It Works

1. Load a WAV file.
2. Analyze. ChopShop detects transients automatically, or you can slice by BPM grid or equal divisions.
3. Adjust. Drag slice markers, add or remove cut points, relabel slices.
4. Generate. Exports individual WAV files for each slice and builds an .aupreset file installed directly to GarageBand's preset folder.

In GarageBand, create a Software Instrument track, open AUSampler, and load the preset. Each chop is mapped to a key starting at the chop root. If you want the sample to continue playing from where it was sliced when pressing a key, play the corresponding cue key, starting at the cue root.

What's Solid, What's Rough

Reliable:

• Transient Detection: I almost always adjust the cuts by hand, but it does a pretty good first job.
• Audio slicing (onset detection, grid, and equal modes) — well-tested and accurate.
• AUSampler preset generation — correctly builds the XML plist with MIDI zone mapping, file references, and all the undocumented boilerplate that AUSampler needs.
• WAV export with optional fade-out and cue zones.
• Interactive waveform — click to preview, drag markers to reposition, double-click to add cuts, right-click to remove.
• CLI with full control over every parameter.

Experimental:

• Auto-labeling (kick, snare, hat, etc.) — uses spectral heuristics that work as rough suggestions, not ground truth. It's good enough to get you started but will frequently mislabel, especially on busy breaks. You can always click a label to change it.
• MIDI pattern generator — generates .mid files with drum patterns mapped to your chopped sounds. Functional, but the built-in patterns are limited and the step editor is basic. Think of it as a starting point for getting a beat down quickly, not a production-ready sequencer. This is actually hilariously bad.

Getting Started

Requires Python 3.10+ and macOS.

git clone https://github.com/larswagoner/sample-chopper.git
cd sample-chopper

python3 -m venv .venv
source .venv/bin/activate
pip install -e ".[gui]"

Then run:

chopshop-gui          # main GUI
chopshop my_break.wav # or use the CLI

If your terminal says "command not found", activate the venv first: source .venv/bin/activate

CLI Usage

# Onset detection (default — finds drum hits automatically)
chopshop my_break.wav

# Grid mode at 170 BPM, 16th notes
chopshop my_break.wav --mode grid --bpm 170 --grid-resolution 16th

# Equal division into 8 slices
chopshop my_break.wav --mode equal --num-slices 8

# Preview slices before generating
chopshop my_break.wav --preview

# Dry run (see what it would do without writing files)
chopshop my_break.wav --dry-run

Run chopshop --help for the full list of options.

Example

The examples/ directory contains a 2.9-second breakbeat loop and the 14 individual chops that ChopShop extracted from it.

Where Files Go

What	Location
Presets	~/Library/Audio/Presets/Apple/AUSampler/
Audio slices	~/Library/Audio/Sounds/ChopShop/<name>/
Chopmaps	~/Library/Audio/Sounds/ChopShop/<name>/<name>.chopmap.json

Guides

• GUI Guide — every control explained.
• MIDI Guide — pattern generator walkthrough.
• Jungle Guide — making 90s jungle in GarageBand with ChopShop.

Development

pip install -e ".[dev]"
pytest

License

MIT