feat(audio): Focusrite 2i2 stereo JACK config for 4CM
Adds: - AudioConfig.mode field: 'mono' (default) or 'stereo_4cm' - capture_channels / playback_channels properties for dynamic JACK -i/-o counts - FOCUSRITE_PROFILES dict with focusrite_2i2_3gen entry - AudioSystem.channel_mapping_help() static method - stereo_4cm port auto-connect wiring (4 cable method) - Systemd service content uses dynamic channel counts - Default config YAML includes 'mode: mono' - 11 new tests (31 total pass) - Focusrite 4CM wiring docs in docs/config-audio.md
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@@ -291,4 +291,68 @@ raspi-gpio get 18 19 20 21
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| 5V | — | Pins 2, 4 | Power | RPi → HAT |
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| GND | — | Pins 6, 9, 14, 25, 30, 34, 39 | Ground | — |
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The I2S HAT uses a **stacking header** (2×20 female socket) to pass through all 40 GPIO pins so footswitches, LEDs, and display are accessible from the top of the HAT.
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The I2S HAT uses a **stacking header** (2×20 female socket) to pass through all 40 GPIO pins so footswitches, LEDs, and display are accessible from the top of the HAT.
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---
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## Focusrite Scarlett 2i2 — 4CM (Four Cable Method)
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> **Interface:** Focusrite Scarlett 2i2 (3rd gen) USB audio interface
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> **Mode:** `stereo_4cm` in `audio.mode`
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> **Device:** `hw:1,0` (USB card index, may vary)
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### Wiring
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```
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Guitar ─────→ Input 1 (ADC channel 0) ─→ hw:1,0 capture_0 ─→ Pipeline input_0
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Amp FX Send ─→ Input 2 (ADC channel 1) ─→ hw:1,0 capture_1 ─→ Pipeline input_1
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Pipeline output_0 (pre-amp) ─→ Output 1 (DAC channel 0) ─→ hw:1,0 playback_0 ─→ Amp Input (Send)
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Pipeline output_1 (post-amp) ─→ Output 2 (DAC channel 1) ─→ hw:1,0 playback_1 ─→ Amp FX Return
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```
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### JACK Config
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```bash
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# Kill PulseAudio first — it grabs USB audio devices
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pulseaudio --kill
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# Start JACK at 48kHz/128 frames, 2 capture + 2 playback channels
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jackd -R -d alsa -d hw:1,0 -r 48000 -p 128 -n 3 -C 2 -P 2
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```
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### Application Config
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Set these fields in `~/.pedal/config.yaml`:
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```yaml
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audio:
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hat_type: "focusrite_2i2_3gen"
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profile: "standard"
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mode: "stereo_4cm"
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input_device: "hw:1,0"
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output_device: "hw:1,0"
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jack_enabled: true
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auto_connect: true
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```
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### Port Auto-Connect
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When `auto_connect: true` and mode is `stereo_4cm`, the system creates these JACK connections:
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| Source | Destination | Signal |
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|--------|-------------|--------|
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| `system:capture_1` | `fx_in:input_0` | Guitar → pre-amp DSP |
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| `system:capture_2` | `fx_in:input_1` | FX Send → post-amp DSP |
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| `fx_out:output_0` | `system:playback_1` | Pre-amp DSP → amp input |
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| `fx_out:output_1` | `system:playback_2` | Post-amp DSP → FX return |
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### Channel Mapping Helper
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At runtime, call `AudioSystem.channel_mapping_help("stereo_4cm")` to get these mappings as structured data.
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### Notes
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- The Focusrite 2i2 registers as ALSA card index **1** when the I2S HAT is card 0 (Linux arranges by driver probe order). If HDMI audio or other USB devices are present, the index may shift — use `aplay -l` / `arecord -l` to confirm.
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- 2-in/2-out at 24-bit/48kHz. JACK runs at 24-bit by default over ALSA.
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- At 48kHz/128 frames × 3 periods, round-trip latency is ~6-8ms — well within the 10ms target for real-time guitar DSP.
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@@ -4,9 +4,10 @@
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- setup (WIP): First-boot setup scripts
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"""
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from .audio import AudioConfig, AudioSystem
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from .audio import AudioConfig, AudioSystem, FOCUSRITE_PROFILES
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__all__ = [
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"AudioConfig",
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"AudioSystem",
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"FOCUSRITE_PROFILES",
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]
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+98
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@@ -53,6 +53,16 @@ I2S_CONFIGS: dict[str, tuple[str, int, str]] = {
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),
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}
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# ── USB audio interface profiles (non-I2S, e.g. Focusrite) ────────
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# Map: short key → (description, expected capture ports, expected playback ports)
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FOCUSRITE_PROFILES: dict[str, tuple[str, int, int]] = {
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"focusrite_2i2_3gen": (
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"Focusrite Scarlett 2i2 3rd gen — USB, 2-in / 2-out, 48 kHz, 24-bit",
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2,
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2,
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),
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}
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# ── JACK latency profiles ─────────────────────────────────────────
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# 48 kHz / 128 frames = 2.67 ms buffer → well under 10 ms RT
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# 48 kHz / 64 frames = 1.33 ms buffer → aggressive, may xrun on RPi 4B
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@@ -89,6 +99,8 @@ class AudioConfig:
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Attributes:
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hat_type: I2S HAT type key from I2S_CONFIGS.
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profile: Latency profile key from LATENCY_PROFILES.
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mode: I/O routing mode: "mono" (default, hw:0,0) or
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"stereo_4cm" (Focusrite 2i2 4-cable-method, 2ch I/O).
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input_device: ALSA hardware device for capture (e.g. hw:0,0).
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output_device: ALSA hardware device for playback (e.g. hw:0,0).
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jack_enabled: Whether to start the JACK server.
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@@ -98,6 +110,7 @@ class AudioConfig:
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hat_type: str = "audioinjector"
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profile: str = "standard"
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mode: str = "mono"
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input_device: str = "hw:0,0"
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output_device: str = "hw:0,0"
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jack_enabled: bool = True
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@@ -127,6 +140,21 @@ class AudioConfig:
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"""JACK ALSA device argument (output device drives JACK master)."""
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return f"d{self.output_device}"
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@property
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def capture_channels(self) -> int:
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"""Number of JACK capture channels (1 for mono, 2 for stereo_4cm)."""
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return 2 if self.mode == "stereo_4cm" else 1
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@property
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def playback_channels(self) -> int:
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"""Number of JACK playback channels (1 for mono, 2 for stereo_4cm)."""
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return 2 if self.mode == "stereo_4cm" else 1
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@property
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def focusrite_profile(self) -> Optional[tuple[str, int, int]]:
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"""Resolve Focusrite profile from hat_type, or None if not a Focusrite."""
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return FOCUSRITE_PROFILES.get(self.hat_type)
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# ═══════════════════════════════════════════════════════════════════
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# Audio system manager
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@@ -246,7 +274,8 @@ class AudioSystem:
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f"-r{profile['rate']}",
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"-dalsa",
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f"-d{self.config.output_device}",
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f"-i2", f"-o2",
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f"-i{self.config.capture_channels}",
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f"-o{self.config.playback_channels}",
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]
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logger.info("Starting JACK: %s", " ".join(cmd))
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@@ -303,6 +332,52 @@ class AudioSystem:
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time.sleep(0.5)
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return self.start_jack(timeout=timeout)
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# ──────────────────────────────────────────────────────────────
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# Channel mapping helpers
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# ──────────────────────────────────────────────────────────────
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@staticmethod
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def channel_mapping_help(mode: str = "mono") -> list[dict]:
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"""Describe the JACK port-to-pipeline channel routing.
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Args:
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mode: ``"mono"`` or ``"stereo_4cm"``.
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Returns:
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List of dicts with keys: capture_port, pipeline_input, pipeline_output,
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playback_port, description.
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Raises:
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ValueError: If *mode* is not recognised.
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"""
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if mode == "mono":
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return [{
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"capture_port": "system:capture_1",
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"pipeline_input": "fx_in:input_0",
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"pipeline_output": "fx_out:output_0",
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"playback_port": "system:playback_1",
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"description": "Guitar → FX chain → Output",
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}]
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elif mode == "stereo_4cm":
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return [
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{
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"capture_port": "system:capture_1",
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"pipeline_input": "fx_in:input_0",
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"pipeline_output": "fx_out:output_0",
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"playback_port": "system:playback_1",
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"description": "Guitar (Input 1) → Pre-amp FX chain → Amp Input (Send)",
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},
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{
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"capture_port": "system:capture_2",
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"pipeline_input": "fx_in:input_1",
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"pipeline_output": "fx_out:output_1",
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"playback_port": "system:playback_2",
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"description": "FX Send (Input 2) → Post-amp FX chain → Amp FX Return",
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},
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]
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else:
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raise ValueError(f"Unknown mode: {mode!r}")
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# ──────────────────────────────────────────────────────────────
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# JACK port connections
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# ──────────────────────────────────────────────────────────────
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@@ -310,17 +385,35 @@ class AudioSystem:
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def connect_fx_ports(self) -> None:
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"""Connect JACK ports for the FX pipeline.
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Default wiring:
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Mono (default):
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system:capture_1 → fx_in:input_0 (guitar → FX chain)
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fx_out:output_0 → system:playback_1 (FX chain → output)
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Stereo 4CM (Focusrite 2i2):
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system:capture_1 → fx_in:input_0 (guitar → pre-amp path)
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system:capture_2 → fx_in:input_1 (FX send → post-amp path)
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fx_out:output_0 → system:playback_1 (pre-amp → amp input)
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fx_out:output_1 → system:playback_2 (post-amp → FX return)
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This is a no-op if jack_connect is unavailable (not in PATH)
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or if any of the target ports don't exist yet.
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"""
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connections = [
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mono_connections = [
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("system:capture_1", "fx_in:input_0"),
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("fx_out:output_0", "system:playback_1"),
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]
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stereo_4cm_connections = [
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("system:capture_1", "fx_in:input_0"),
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("system:capture_2", "fx_in:input_1"),
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("fx_out:output_0", "system:playback_1"),
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("fx_out:output_1", "system:playback_2"),
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]
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connections = (
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stereo_4cm_connections
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if self.config.mode == "stereo_4cm"
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else mono_connections
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)
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for src, dst in connections:
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try:
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subprocess.run(
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@@ -535,7 +628,8 @@ class AudioSystem:
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exec_start = (
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f"/usr/bin/jackd -P{profile['rt_priority']} "
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f"-p{profile['period']} -n{profile['nperiods']} "
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f"-r{profile['rate']} -dalsa -d{config.output_device} -i2 -o2"
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f"-r{profile['rate']} -dalsa -d{config.output_device} "
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f"-i{config.capture_channels} -o{config.playback_channels}"
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)
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return f"""[Unit]
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Description=JACK Audio Server — Pi Multi-FX Pedal
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@@ -20,6 +20,7 @@ DEFAULT_CONFIG: dict = {
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"audio": {
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"hat_type": "audioinjector",
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"profile": "standard",
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"mode": "mono",
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"input_device": "hw:0,0",
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"output_device": "hw:0,0",
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"jack_enabled": True,
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@@ -10,6 +10,7 @@ from system.audio import (
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AudioSystem,
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LATENCY_PROFILES,
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I2S_CONFIGS,
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FOCUSRITE_PROFILES,
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CONFIG_TXT,
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JACK_SERVICE_PATH,
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LIMITS_CONF,
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@@ -187,6 +188,73 @@ def test_systemd_service_content_custom_device():
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assert "-dhw:2,0" in content
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# ── Mode / stereo_4cm tests ───────────────────────────────────────
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def test_audio_config_mode_default():
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cfg = AudioConfig()
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assert cfg.mode == "mono"
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def test_audio_config_mode_stereo_4cm():
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cfg = AudioConfig(mode="stereo_4cm")
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assert cfg.mode == "stereo_4cm"
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def test_audio_config_channel_counts_mono():
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cfg = AudioConfig(mode="mono")
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assert cfg.capture_channels == 1
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assert cfg.playback_channels == 1
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def test_audio_config_channel_counts_stereo_4cm():
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cfg = AudioConfig(mode="stereo_4cm")
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assert cfg.capture_channels == 2
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assert cfg.playback_channels == 2
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def test_audio_config_focusrite_profile_hit():
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cfg = AudioConfig(hat_type="focusrite_2i2_3gen")
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prof = cfg.focusrite_profile
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assert prof is not None
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desc, cap, play = prof
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assert "Focusrite" in desc
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assert cap == 2
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assert play == 2
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def test_audio_config_focusrite_profile_miss():
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cfg = AudioConfig()
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assert cfg.focusrite_profile is None
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def test_focusrite_profiles_entries():
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for key, (desc, cap, play) in FOCUSRITE_PROFILES.items():
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assert len(desc) > 10
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assert isinstance(cap, int) and cap > 0
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assert isinstance(play, int) and play > 0
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def test_channel_mapping_help_mono():
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mapping = AudioSystem.channel_mapping_help("mono")
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assert len(mapping) == 1
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assert mapping[0]["capture_port"] == "system:capture_1"
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assert mapping[0]["playback_port"] == "system:playback_1"
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def test_channel_mapping_help_stereo_4cm():
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mapping = AudioSystem.channel_mapping_help("stereo_4cm")
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assert len(mapping) == 2
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assert "Guitar" in mapping[0]["description"]
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assert "FX Send" in mapping[1]["description"]
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def test_channel_mapping_help_unknown():
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import pytest
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with pytest.raises(ValueError, match="Unknown mode"):
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AudioSystem.channel_mapping_help("bogus")
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# ── Module exports ────────────────────────────────────────────────
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