# Raspberry Pi PipeWire Audio Hub

Turn a headless **Raspberry Pi 4** + **Universal Audio Volt 4** USB interface into a
multi-source audio hub built around an analog mixer:

- a **phone** plays in over **Bluetooth** (A2DP),
- one or more **desktops** play in over the **wired LAN** (PipeWire/PulseAudio network),
- the mixer's **main output** is captured back and **re-published on the network** so
  **OBS** machines can record it.

```
Phone (Bluetooth) ───────────────────────▶ Volt OUT 1/2 ─┐
Desktop (default sink) ──────────────────▶ Volt OUT 1/2 ─┤
                                                          ├─▶ MIXER ─▶ main out
Desktop ("Desktop (Volt 3/4)" sink) ─────▶ Volt OUT 3/4 ─┘            │
                                                                      │
        OBS machines ◀── network ◀── Volt IN 3/4 ◀────────────────────┘
```

The Pi does **no software mixing** — it just feeds the Volt's outputs and captures
its inputs. All levels/EQ/mute live on the physical mixer.

## What's in this repo

| Path | What it is |
|---|---|
| **`RUNBOOK.md`** | Build from a blank SD card, step by step (the install guide). |
| **`MAINTENANCE.md`** | How a built hub is wired together + day-to-day upkeep (operate it). |
| **`config/`** | The actual PipeWire/WirePlumber drop-in files, as deploy-ready templates. |
| **`systemd/`** | `bt-agent.service` — headless auto-accept Bluetooth pairing. |
| **`firmware/`** | The `/boot/firmware/config.txt` lines to set (disable HDMI/onboard audio + Wi-Fi). |
| **`instances/`** | Per-deployment real values (host, IP, Volt serial, phones). E.g. `instances/adac.md`. |

The docs use placeholders — `<pi-host>`, `<pi-ip>`, `<lan-cidr>`, `<VOLT_SOURCE>`,
`<VOLT_SINK>` — filled in per box from the matching `instances/` file.

## Deploying to a Pi

`RUNBOOK.md` is the authoritative walkthrough. In short, once the OS + packages are
in place (RUNBOOK §1–§2):

1. Copy `config/` into `~/.config/` for the `user` account (PipeWire runs per-user).
2. In `30-mixer-return.conf` / `40-desktop-34.conf` replace `<VOLT_SOURCE>` /
   `<VOLT_SINK>` with this unit's real node names (the commands are in each file's
   header comment), and put your subnet in `20-network.conf` (`<LAN_CIDR>`).
3. Install `systemd/bt-agent.service` to `/etc/systemd/system/` and
   `enable --now` it.
4. Apply the `firmware/config.txt.snippet` edits and reboot.
5. `MAINTENANCE.md` §7 has the health checks to confirm it all came up.

> The deployed Pi also carries two on-box READMEs (a `/root` redirect to "log in as
> `user`", and a copy of `MAINTENANCE.md` at `/home/user/README.md`). The redirect's
> text is `root-README.md` in this repo.