ETH-68: Ethernet Audio Interface for Linux

The ETH-68 is an Ethernet‑based audio interface that runs custom bare‑metal firmware on an STM32H7 microcontroller, presenting itself to a host computer as a netJACK1 master endpoint. Users initiate audio exchange by launching a JACK server with the netone backend (e.g., `jackd -d netone`), after which the first incoming capture packet causes JACK to create I/O ports that correspond to the physical inputs and outputs of the ETH‑68. The device can also be accessed directly from a PipeWire session using the `pw-eth68` client, which mimics the netone‑based JACK behavior, allowing PipeWire‑aware applications to connect to the same ports.

A key performance metric of the ETH‑68 is its exceptionally low round‑trip audio latency. Measured with a loopback cable and the `jack_delay` utility, the interface achieves 3.620 ms of latency at 48 kHz with a 64‑sample buffer, well within the 5–20 ms perception threshold for most listening contexts. At 96 kHz the latency improves further, surpassing a comparable RME card by 0.33 ms. The system also provides a 3.3 V “LATMON” digital signal on a rear‑panel BNC connector, enabling precise measurement of processing latency and jitter; typical cycles show about 625 µs of processing time, leaving a comfortable margin before the 1.333 ms deadline for 64‑sample buffers at 48 kHz, even under moderate DSP load in a Bitwig project.

Multiple ETH‑68 units can be synchronized to expand channel count, though this requires an intermediate proxy application (`eth68proxy`) when using JACK because netJACK does not natively merge or split data from several masters. The proxy merges capture packets from each unit into a single netJACK‑compatible packet and splits playback packets back to the individual devices, preserving the single‑unit latency while adding only a negligible processing overhead. When operating through PipeWire, `pw-eth68` handles multi‑unit stream management, eliminating the need for the proxy. Network configuration defaults to sending capture packets to 12.12.12.10:3000, but settings can be altered with the `eth68ctl.py` script, facilitating flexible deployment in various audio production environments.

⚡ Effects Interpreter