Other Software

pi-Stomp is intended to be a platform. MOD is the recommended software for audio processing and configuration, and it's what ships.

But...

There is a good chance that other audio software which uses JACK will "just work". You can install it on top of the pi-Stomp image and switch between them.

Reaching the JACK server

JACK runs as the jack user, promiscuous and restricted to the jack group. pistomp is in that group. Clients must be told where to look:

export JACK_PROMISCUOUS_SERVER=jack

Without it, every JACK tool reports "jack server is not running" while it is running. With it, jack_lsp lists all 66 ports. The stock services set the variable themselves; see systemctl cat mod-host.

Getting a display

Most JACK applications render to an application window. The image is headless. Use one of the following; neither requires a desktop environment.

X11 forwarding, if you have an X server (XQuartz on macOS, built in on Linux). sshd already permits it:

ssh -X pistomp@pistomp.local

A virtual display plus VNC, which survives a dropped SSH session:

sudo apt install xvfb x11vnc
Xvfb :99 -screen 0 1024x768x24 &
DISPLAY=:99 x11vnc -localhost -nopw -bg

x11vnc is bound to localhost. Tunnel it:

ssh -L 5900:localhost:5900 pistomp@pistomp.local

Point a VNC viewer at localhost:5900.

Guitarix — worked example

Guitarix is a JACK-native amp simulator, and the project behind the Gx* plugins already on your device.

sudo apt install guitarix
export JACK_PROMISCUOUS_SERVER=jack
DISPLAY=:99 guitarix &

It registers two clients, gx_head_amp and gx_head_fx. Connect them to the hardware:

jack_connect system:capture_1 gx_head_amp:in_0
jack_connect gx_head_fx:out_0 system:playback_1

Verified on the current image with jack, mod-host, mod-ui and the pi-Stomp controller running.

Freeing the machine

MOD consumes CPU and holds the connections to the hardware playback ports. Release them:

sudo systemctl stop mod-host mod-ui

disable makes it persist across reboots; sudo systemctl enable --now mod-host mod-ui reverses it. Leave jack running.

To keep the footswitches and knobs, restart the controller in generic mode. It reads the controls and sends their MIDI CCs without requiring MOD:

ps-stop
ps-run --host generic

Add --host generic to ExecStart in the service file to persist. The encoders and LCD have no assigned function in this mode. Stop mod-ala-pi-stomp entirely if the hardware controls are not needed.

Known not to work

The wiki's older page on this is written for Patchbox OS — patchbox boot environment desktop, the modep- service prefix, armhf packages. None of it applies to the current image.

Reverting

Nothing above modifies the pi-Stomp software:

sudo apt remove --purge guitarix xvfb x11vnc
sudo apt autoremove
sudo systemctl enable --now mod-host mod-ui
ps-restart