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The appliance build: a handheld that is only SignalPatch

Target rig: ASUS ROG Ally (Z1 Extreme) + Zoom F4 as a dedicated guitar patching studio, voice processor and synth. This document is the concrete build guide. Short answer to "Linux or Windows?": Linux, stripped down, for three reasons — you control the scheduler and audio stack completely, the machine does nothing else (no updaters, overlays or game bars stealing the CPU mid-song), and JACK/PipeWire at a 64-sample quantum is reliably achievable. Windows works (notes at the end) but is the fallback, not the recommendation.

Latency reality check

"No latency" budget = converters + USB + 2× buffer. At 48 kHz / 64 samples the software adds 2.7 ms; the F4's converters and USB framing add roughly 2–4 ms more. Total round trip in the 5–7 ms range — tighter than standing two metres from your amp. 32 samples halves the software share when the patch's worst case allows it.

The two tools that tell you whether a patch fits the deadline:

  • The header readout DSP x% (pk y%) — pk is the worst-case block. If pk stays under ~60% at your buffer size, the patch will not glitch.
  • The model benchmark: SIGNALPATCH_BENCH_NAM_DIR=~/nam-models ./signalpatch_tests prints avg/worst cost per model with an OK / TIGHT / OVER verdict.

Measured on a desktop Zen3 core at 64/48k (the Ally's Z1E is comparable): Boss LSTM captures 5–9% average, feather WaveNet ~11% average / ~50% worst case. Rule of thumb: stack LSTM pedal captures freely (3–5 in a chain), budget WaveNets one per patch, and re-run the benchmark on the Ally itself.

Base system (Linux)

  1. Distro: minimal Debian (netinst, "standard system utilities" only) or Arch. No desktop environment — the app is the desktop.
  2. Packages: pipewire pipewire-jack wireplumber cage greetd (or plain Xorg + xinit if you prefer X11), plus the build dependencies from the README if compiling on-device.
  3. Realtime privileges — /etc/security/limits.d/audio.conf: 
    @audio - rtprio 95
@audio - memlock unlimited
    Add your user to the audio group.
  4. PipeWire quantum — ~/.config/pipewire/pipewire.conf.d/lowlatency.conf: 
    context.properties = {
    default.clock.rate = 48000
    default.clock.quantum = 64
    default.clock.min-quantum = 32
    default.clock.max-quantum = 64
}
  5. CPU: performance governor (cpupower frequency-set -g performance via a systemd unit), and on the Ally set the TDP profile high while plugged in.
  6. USB: disable autosuspend for the F4 (usbcore.autosuspend=-1 on the kernel cmdline is the blunt, reliable option for a dedicated box).
  7. Silence the box: systemctl disable --now bluetooth cups avahi-daemon and anything else the machine doesn't need to be an instrument.

Boot-to-instrument

greetd config (/etc/greetd/config.toml) starting a cage kiosk as your user:

[initial_session]
command = "cage -- env PIPEWIRE_LATENCY=64/48000 SignalPatch --kiosk --unmute /home/USER/live.signalpatch"
user = "USER"
  • --kiosk = fullscreen, no window chrome.
  • --unmute = skips the restore-muted safety pause. This is the explicit opt-in for a dedicated machine; leave it off on a desktop.
  • The patch argument is optional — without it the last session is restored.

Result: power button → your patch, sounding, in well under a minute. The Zoom F4 is picked automatically on first boot (device preference), and the choice persists.

Zoom F4 notes

  • Use the F4's audio-interface (pro audio) mode; SignalPatch sees all six inputs and four returns as individual patch ports.
  • Set input gain on the F4's preamps; keep SignalPatch's input trims near 0 and do creative gain staging in the graph.
  • Monitor through the F4 headphone out or its main outs — that is the low-latency path being measured.

Models on the appliance

Put your .nam captures in ~/Documents/SignalPatch/models (or point SIGNALPATCH_MODELS_DIR anywhere). The Neural Amp and Neural Pedal modules step through that folder with their ◀ ▶ buttons — a pedal library on two buttons, which maps directly onto handheld shoulder keys later (roadmap 0.6). Each neural module shows its own cost ("- x% of block") so you can see which capture is eating the budget while you play.

Windows fallback (the Ally's native OS)

Works, with caveats: install Zoom's ASIO driver for the F-series, run SignalPatch with -DSIGNALPATCH_ENABLE_ASIO=ON built in, pick the ASIO backend and 64 samples in AUDIO SETUP. Then fight the OS: High Performance power plan, disable Game Bar/Game Mode overlays, Armoury Crate silent updates, and scheduled maintenance. A Task Scheduler entry can launch SignalPatch.exe --kiosk --unmute patch.signalpatch at logon. Expect a few ms more jitter than the Linux build and re-run the benchmark to confirm your chains still fit.

Freeze it

Once the rig works, stop updating it. It is an instrument now: no unattended upgrades, no new kernels before a gig, and keep a known-good SD/USB image of the whole system so the appliance can be re-flashed in minutes.