Raspberry Pi MIDI Sampler

A real-time MIDI sampler for Raspberry Pi that transforms your Circuit Tracks into a powerful dual-channel chromatic sampler.
Uses both MIDI tracks from the Circuit Tracks, mapping each to a separate chromatic sampler and routing them to the left and right audio outputs.

Dependencies

First, install required packages on your Raspberry Pi:

./setup.sh

Important: Log out and log back in after setup for audio group permissions.

Quick Start

make
./sampler

That's it! The sampler automatically:

• Tests multiple JACK configurations to find one that works
• Tries 48kHz, 44.1kHz, and different buffer sizes
• Works with USB audio, onboard audio, or plugin layer
• Connects to your audio outputs automatically
• No manual configuration needed!

MIDI Device Scanner

List connected USB MIDI devices:

make midi
./list_midi

Requirements

• Raspberry Pi 3/4 (1GB+ RAM for Pi 3, 2GB+ for Pi 4)
• JACK Audio Connection Kit
• USB MIDI Interface (or built-in audio for basic use)
• High-speed SD card (Class 10+)
• Audio interface (USB recommended, built-in 3.5mm supported)

Installation & Auto-Start

After running setup.sh, the install.sh script sets up the sampler to run on boot:

./install.sh

What it does:

• Builds the sampler executable
• Creates ~/samples/ directory for your audio files
• Installs SystemD service for auto-start on boot
• Configures real-time audio priority settings

Run as your regular user (not root) - the script adapts to any username.

Configuration

Place samples in ~/samples/ directory (WAV format).

Edit audio_config.txt for engine settings:

• master_gain: Overall volume (0.1-1.0)
• max_voices: Polyphony limit (2-16)
• auto_gain_control: Automatic volume scaling
• jack_client_name: JACK client identifier

Features

• Professional latency: <5ms with JACK (vs 20-50ms with ALSA)
• Zero underruns: JACK handles all timing automatically
• Polyphonic: Up to 16 simultaneous samples
• Sample rate conversion: Automatic resampling to JACK rate
• Auto-connect: Connects to system outputs automatically
• Modular architecture: Separate JACK client and audio engine

Manual JACK Commands (if needed)

# Check JACK status
jack_lsp                    # List JACK ports
jack_lsp -c                 # List connections
qjackctl                    # GUI control (if installed)

# Manual JACK start (if auto-start fails)
./start_jack.sh             # Use the auto-detection script
# OR
jackd -dalsa -dhw:0 -r48000 -p1024 -n2 &   # 48kHz standard

# Connect manually (if auto-connect fails)
jack_connect rpi-sampler:out_left system:playback_1
jack_connect rpi-sampler:out_right system:playback_2

Service Management

sudo systemctl start rpi-sampler-$USER     # Start service
sudo systemctl stop rpi-sampler-$USER      # Stop service  
sudo systemctl status rpi-sampler-$USER    # Check status
sudo journalctl -u rpi-sampler-$USER -f    # View logs

Service name format: rpi-sampler-{username} (e.g., rpi-sampler-john)

Troubleshooting

"Failed to start JACK automatically":

• Check audio group: groups should include audio
• List audio devices: aplay -l
• Manual start: ./start_jack.sh

"Cannot connect JACK client":

• Kill existing JACK: killall jackd
• Check device permissions: ls -l /dev/snd/
• Try manual start: jackd -dalsa -dhw:0 -r48000 -p1024 -n2 &

"No audio output":

• Check connections: jack_lsp -c
• Manual connect: jack_connect rpi-sampler:out_left system:playback_1