Technical Constraints
The analysis runs in Python, and publication could not depend on its readers: a slow, stalled, or crashed consumer must never be able to hold up the capture loop.
Engineering Case Study
Aether
Linux audio-analysis daemon that publishes live frequency-band state through a sequence-versioned shared-memory region for independent local consumers.
Problem
Desktop audio tooling is usually built as isolated effects or visualizers. Aether treats live audio analysis as shared system state so multiple processes can react to the same stream without each opening their own capture path.
Constraints
Environment
Aether targets a single Linux workstation: PipeWire for capture, a RAM-backed file in /dev/shm for publication, optional systemd user services, and OpenRGB for lighting.
Tradeoffs
Aether publishes only the latest snapshot. Readers never block the writer, but there is no queue, no backpressure, and no delivery guarantee: a reader that polls more slowly than the daemon publishes misses frames.
Architecture
- The daemon reads 16-bit mono audio from PipeWire's pw-record at 48 kHz in 2,048-sample chunks. That configuration sets a nominal cadence of about 23 chunks per second; it is not a measured update rate.
- Each chunk is Hann-windowed and passed through an FFT to produce seven normalized frequency bands between 20 Hz and 8 kHz, plus a total-energy value. Chunks below a configured energy threshold are not published.
- Published frames go into a 4 KB memory-mapped file: a fixed 20-byte binary header (magic, protocol version, 64-bit sequence number, payload length) followed by a JSON payload.
- Consumers attach independently and read that region directly: the terminal visualizer, the OpenRGB lighting controller, and a small client library used by a command-line query tool and the status-bar, Hue, OBS, Discord, and notification integrations.
- The repository includes systemd user units that start the daemon after PipeWire, start the Hue, OBS, Discord, and notification services after it, and restart them on failure.
Key Technical Decisions
Latest-value snapshot, not a message stream
Consumers need current acoustic state, not history. One overwritable snapshot means a slow or stalled reader can never back up the daemon. The cost is lossy delivery: frames a reader is too slow to see are gone, with no acknowledgement or replay.
Seqlock instead of a lock
The writer marks a frame in progress with an odd sequence number and commits it with the next even one; readers compare the sequence before and after reading. Readers never block the writer. In exchange, readers discard frames that changed mid-read, and the protocol assumes a single writer, which the code does not enforce.
Fixed header, JSON payload
Only the header is a binary layout; the band data is JSON. A reader needs just the header format and a JSON parser, at the cost of serializing every frame on write and parsing it on read. The exchange is not zero-copy.
systemd user services for orchestration
Audio infrastructure should start with the session, restart on failure, and stay decoupled from the terminal used to launch it.
Tested Behavior
Readers reject unusable frames
A reader accepts a frame only if its sequence number is nonzero, even, unchanged across the read, and different from the last frame it consumed. Eight deterministic tests cover each rejection case, a round trip, and in-order delivery; all eight passed in CI at the pinned commit.
The visualizer goes quiet when frames stop
If no audio frame arrives for 0.1 seconds, the terminal visualizer releases its target amplitude and eases into its quiet state. Two engine tests cover the expiry and its reset; both passed in the same CI run.
Result and Limitations
- Result: at commit 71e0201, the seqlock protocol tests and the visualizer's quiet-state tests pass in CI. That establishes the reader rules described above. It is not a performance measurement, and no latency or throughput figure is claimed.
- Test scope: the protocol tests are single-process and deterministic, and the torn-read case is simulated with a substitute memory map. Concurrent multi-process stress is untested, and the tests do not establish correctness on weaker memory-ordering architectures.
- Limitation: freshness is not part of the contract. A reader cannot tell a stopped daemon from audio below the publishing threshold. The visualizer expires stale input, but the client library returns its last values indefinitely, so integrations built on it can hold stale state.
- Limitation: attachment is not uniform. The OpenRGB controller retries until the shared-memory file exists; the client-based integration services exit and rely on systemd to restart them; the terminal visualizer does not reattach if it starts before the daemon has created the file.
Evidence
Repository provenance / Public
Repository provenance
Public source history for the Linux audio daemon remains on the legacy repository account where the project was developed.
Note: Canonical contact identity remains github.com/kareemsasa; this repository has not migrated.
View artifactEvaluation record / Public
Seqlock protocol tests
Eight deterministic tests of the reader rules: committed, uninitialized, in-progress, already-seen, and changed-mid-read frames, plus round-trip and in-order delivery.
Note: Pinned to commit 71e0201. Single-process tests, not a concurrency stress test or a performance benchmark.
View artifactEvaluation record / Public
CI run for the pinned commit
GitHub Actions run on commit 71e0201 (August 27, 2026). The seqlock, engine, and full pytest steps passed.
View artifactRepository provenance / Public
Shared-memory implementation
The writer and reader that implement the header layout and sequence rules described above.
Note: Pinned to commit 71e0201.
View artifactRepository provenance / Public
systemd integration
The user unit and installer for running the daemon as a systemd user service.
Note: Integration source, not a record of a running deployment.
View artifact