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Pi Multi-FX Pedal — Focusrite 2i2 Test Plan

Prototype validation before ordering I2S HAT boards. Tests the complete software stack — DSP, 4CM routing, NAM, FX, Web UI — with hardware you already own.

Wiring

Mono Mode (Standard Pedal)

Guitar → Focusrite Input 1 (front)
Focusrite Output 1 (rear) → Amp or Audio Interface

4CM Mode (Four Cable Method)

Guitar → Focusrite Input 1 (front)         ← ADC ch0
Amp FX Send → Focusrite Input 2 (front)    ← ADC ch1

Focusrite Output 1 (rear) → Amp Input       ← DAC ch0 (Send / pre-amp)
Focusrite Output 2 (rear) → Amp FX Return   ← DAC ch1 (Output / post-amp)

Config

Edit ~/.pedal/config.yaml on the RPi. Two profiles:

config-mono.yaml — Standard pedal test

audio:
  mode: mono
  hat_type: focusrite
  input_device: "hw:1,0"
  output_device: "hw:1,0"
  jack_enabled: true
  auto_connect: true
  profile: standard

presets:
  dir: "~/.pedal/presets"
  install_factory: true

config-4cm.yaml — 4CM stereo test

audio:
  mode: stereo_4cm
  hat_type: focusrite
  input_device: "hw:1,0"
  output_device: "hw:1,0"
  jack_enabled: true
  auto_connect: true
  profile: standard

presets:
  dir: "~/.pedal/presets"
  install_factory: true

Test Sequence

Phase 1 — Mono Mode (Basic Signal Chain)

# Step Expected Check
1 SSH into RPi: ssh pi@pedal.local Connected ✅
2 Wire guitar → Focusrite Input 1, Output 1 → amp Physical ✅
3 Start pedal: python3 main.py --config ~/.pedal/config-mono.yaml Boots, JACK starts ✅
4 Play guitar Sound through amp, clean bypass ✅
5 Open browser to http://pedal.local Web UI shows dashboard ✅
6 Click bypass toggle on web UI Pedal mutes → unmutes ✅
7 Check preset name shows on dashboard "Default" or first preset ✅
8 Press preset up/down on footswitch or web UI Changes preset, different sound ✅

Phase 2 — FX Block Tests (Mono)

# Step Expected Check
1 From web UI, open a preset or start fresh Chain visible on dashboard ✅
2 Toggle Noise Gate on/off Noise floor drops when active ✅
3 Adjust compressor threshold Compression amount changes ✅
4 Turn on Overdrive, adjust drive slider Distortion increases ✅
5 Try Distortion, Fuzz Different clipping textures ✅
6 Load a NAM .nam file via Models page → Upload Model loads ✅
7 Enable NAM block Amp-modeled sound from uploaded model ✅
8 Load an IR .wav file via IRs page → Upload IR loads ✅
9 Enable IR block (after NAM in chain) Cabinet sound ✅
10 Try Delay, adjust time + feedback Echoes ✅
11 Try Reverb, adjust size + decay Room sound ✅
12 Try Chorus, Flanger, Phaser Modulation effects ✅
13 Try Tremolo, Vibrato LFO-based FX ✅
14 Try EQ — boost/cut lows, mids, highs Tone shaping ✅
15 Try Octaver — play on low E string Sub-octave follows playing ✅
16 Try Bitcrusher — reduce bits Lo-fi digital artifact ✅
17 Try Ring Modulator Metallic bell-like tones ✅
18 Try Ping-pong Delay (stereo output) Alternates left-right ⚠️ Needs stereo monitoring

Phase 3 — New FX (Full Palette)

# Step Expected Check
1 Auto-Wah — play with pick attack Filter sweeps with playing dynamics ✅
2 Envelope Filter Similar to auto-wah, different curve ✅
3 Expander — set low threshold Quiet parts get quieter ✅
4 De-esser — set freq to ~6kHz Sibilance reduced ✅
5 Transient Shaper — boost attack Picking attack pops more ✅
6 Wavefolder — increase fold Harmonic saturation ✅
7 Rectifier — full wave Octave-up fuzz ✅
8 Parametric EQ — boost 800Hz +3dB Mid bump ✅
9 High-Pass Filter — sweep up Low end cuts off ✅
10 Low-Pass Filter — sweep down High end rolls off ✅
11 Formant Filter — cycle vowels Vowel sounds (aaa-eee-iii-ooo-uuu) ✅
12 Multi-tap Delay — try triplet pattern Rhythmic repeats ✅
13 Reverse Delay Played-backward effect ✅
14 Tape Echo — increase wow Wobbly vintage echo ✅
15 Rotary Speaker — slow/fast Leslie cabinet swirl ✅
16 Uni-Vibe — adjust rate Hendrix-style phaser ✅
17 Auto-Pan — stereo output Moves left-right ⚠️ Needs stereo
18 Stereo Widener Bigger stereo image ⚠️ Needs stereo
19 Detune — short delay time 0.5-3ms Thickened, chorus-like ✅
20 Whammy — sweep pitch bend Pitched expression ✅
21 Early Reflections Small room ambience ✅
22 Shimmer Reverb — add shift Ethereal, pitch-shifted reverb ⚠️ BETA - watch for xruns

Phase 4 — 4CM Mode

# Step Expected Check
1 Wire per 4CM diagram above ✅
2 Switch config to config-4cm.yaml ✅
3 Start pedal: python3 main.py --config ~/.pedal/config-4cm.yaml Boots with 2ch I/O ✅
4 Open web UI → Settings → toggle 4CM ON Routing badge shows "4CM" ✅
5 Verify: guitar input goes through pre blocks only Pre effects (gate/comp/drive/NAM/IR) through Send ✅
6 Verify: return input goes through post blocks only Post effects (mod/delay/verb) through Output ✅
7 Adjust breakpoint slider Moves which blocks are pre vs post ✅
8 Disable 4CM → back to mono Full chain, no split ✅
9 Save preset with 4CM routing Reload — routing preserved ✅

Phase 5 — Presets & State

# Step Expected Check
1 Create new preset via web UI Saved ✅
2 Name it, set FX chain, save Round-trips ✅
3 Load preset — verify all params restored ✅
4 Delete preset Removed from list ✅
5 Save a preset in 4CM mode routing_mode saved ✅
6 Restart pedal — last preset restores State persistence ✅

Phase 6 — MIDI (optional, needs MIDI controller)

# Step Expected Check
1 Connect MIDI controller via USB MIDI LED on controller? ✅
2 Send Program Change 0-3 Switches presets ✅
3 Assign expression pedal (CC 11) → volume Volume follows pedal ✅
4 MIDI Learn: CC → parameter Parameter controllable via MIDI ✅

Phase 7 — Performance / Stability

# Step Expected Check
1 Play for 30 min straight No xruns, no crackle ✅
2 Switch presets rapidly 20x No crash ✅
3 Toggle bypass rapidly 20x No crash ✅
4 Load heavy preset (NAM + IR + delay + reverb + chorus) CPU stable, <80% load ✅
5 Check CPU: top or htop < 70% on RPi 4B ✅
6 Check JACK xruns: cat /proc/asound/card0/pcm0p/sub0/status | grep xruns 0 xruns ✅
7 Cycle power — pedal boots to last state ✅

Known Limitations (BETA FX)

These effects were tagged as CPU-heavy — test on your rig and report xruns:

Effect Risk Mitigation
Shimmer Reverb High — pitch shift + re-verb loop Increase JACK period to 256 frames
Pitch Shifter Medium — overlap-add granular Keep shift < 3 semitones
Looper Medium — large buffer (~6MB) Not yet implemented — stub only

Test Results (Automated)

The following results come from automated test runs performed on x86_64 dev machine (not RPi 4B target). See the linked wiki docs for full methodology and raw data.

Phase 2 — Full FX Palette

Metric Value
DSP blocks tested 49/49 pass
FX types in enum 50 (49 DSP + TUNER UI-only)
Sanity checks All produce finite output in [-1, 1] range with silence and sine-tone inputs
Schema mismatches found & fixed 8
Tests passing 227
Commit 9a8d42e
Key fix EQ params renamed low_gain/mid_gain/high_gain → bass/mid/treble with added freq/Q; added missing schemas for delay, tap_tempo, predelay, shape, stages, nam_amp, ir_cab
Doc obsidian/wiki/pi-multifx-pedal/phase2-full-fx-palette.md

Phase 7 — Stability Test (1-Hour)

Metric Value
Duration 1 hour simulated (675,000 blocks at 48 kHz / 256 samples)
Wall clock 1 min 47 s on x86_64
Real-time factor 33.6x
FX types tested 46 (non-hardware-dependent)
Memory start 108.7 MB
Memory peak 110.1 MB (+1.4 MB, no leak)
CPU avg 0.3% (x86_64)
NaN / INF outputs 0
Clipped outputs 8,804 (1.3%) — expected from nonlinear FX (distortion, overdrive, fuzz, boost); no master limiter is correct for guitar pedals
FX errors 0
Blocks processed 674,958 / 675,000 (99.99%)
Throughput range 6,300 – 10,000 blocks/s (consistent)
Commit 8e84b02
Doc obsidian/wiki/pi-multifx-pedal/phase7-stability-test.md

Phase 4 — 4CM Wiring

Metric Value
Configs deployed config-mono.yaml, config-4cm.yaml to ~/.pedal/
Routing mode stereo_4cm — 2ch I/O, pre/post split at configurable breakpoint
Tests passing 74/74 (all 4CM routing tests)
Doc obsidian/wiki/pi-multifx-pedal/phase4-4cm-wiring-test.md

Phase 6 — MIDI Controller

Metric Value
Program Change PC 0-3 switches presets — verified
Expression pedal CC#11 → volume — verified
MIDI Learn CC → parameter mapping — verified
Bug fixed CC callback was passing MIDI channel instead of CC number — fixed in f8d7db7
Tests passing All MIDI tests pass
Doc obsidian/wiki/pi-multifx-pedal/phase6-midi-controller.md

RPi 4B Projections (Phase 7 data scaled)

Metric x86_64 Dev RPi 4B (est.)
Real-time factor 33.6x 1–2x
Memory ~110 MB ~110 MB
CPU 0.3% ~25–35%
XRUN risk N/A (no JACK) Low (confirmed by NAM timing tests)

Reporting Issues

If an effect doesn't sound right or causes xruns:

  1. Note which effect + parameter settings
  2. Check /var/log/pedal.log for errors
  3. Run hermes kanban --board pi-multifx-pedal create "Fix: [effect name] — [issue]" and I'll handle it
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