LTBR·FM Receiver

A rock-solid, cross-platform desktop radio player for the London Tower Block Radio Icecast stream — with a functional 10-band graphic equaliser and a live LED spectrum analyser, wrapped in a brushed-metal "rack unit" interface.

🔊 Listen right now, no install needed: the station's web player lives at www.ltbr.fm/player — this app is its desktop counterpart, downloadable from the same page.

What it is

• Native Rust audio engine. The stream is decoded (MP3), equalised and mixed entirely in Rust — no reliance on the system webview's codecs, so it behaves identically on Linux, Windows and macOS.
• Functional graphic EQ. Ten bands (31 Hz – 16 kHz) plus a preamp, with Flat / Pirate / Bass / Voice presets. Every band actually shapes the audio.
• Artifact-free controls. All gains (EQ, preamp, volume, mute) are smoothed on the audio thread, so dragging any slider — even fast, even to the extremes — produces no clicks, pops or zipper noise.
• Live spectrum + two-line dot-matrix display driven by the real post-EQ signal. The top line carries the station and the current track; the bottom line cycles through the next track with a live countdown, the programme and the DJ on air — all decoded from the station's in-band ICY metadata.
• Stays on the live edge. Metadata is released in step with the audio, so the display never runs ahead of what you hear — and the same timing anchor measures how far behind the live edge you are. Drift beyond 15s is trimmed back to the ~8s target, falling back to a silent reconnect if trimming will not hold.
• Resilient. Automatic reconnection with backoff; a dropped network never crashes the app.
• Three faces. Right-click → Face switches between the default rack unit, a Vintage 80s UK receiver — a backlit tuning dial with a real analogue feel, turn the knob through inter-station static until LTBR·FM locks in, plus twin VU meters and rotary volume — and Mini, a compact strip about a quarter of the footprint that keeps playing while the chrome tucks away. The choice is remembered.

Default stream: https://stream.ltbr.fm/live (any Icecast/SHOUTcast MP3 URL works — type one in the Stream box and press Tune).

Architecture

Rust engine (background threads)
  reqwest ─▶ ICY metadata demux ─▶ symphonia (MP3 decode)
    ─▶ 10 biquad bands + preamp + volume   (all per-sample smoothed)
    ─▶ rubato resample → cpal output       (WASAPI / CoreAudio / ALSA)
       └▶ rustfft ─▶ 20 log bars ─▶ UI event
  state machine: standby │ tuning │ live │ error  ─▶ UI event
  ICY StreamTitle + StreamUrl ─▶ decode ─▶ held until the audio it
    describes reaches the speakers ─▶ "nowplaying" / "metadata" UI events
       └▶ lag vs. the live edge ─▶ trim or resync ─▶ "sync" UI event

Frontend (Tauri webview, vanilla TS)
  Renders the interface + canvases; sends control intents over IPC.

Source map:

Area	File
UI wiring / IPC	src/main.ts
Canvas scroller + spectrum	src/visuals.ts
EQ / preamp / volume DSP	src-tauri/src/dsp.rs
Spectrum FFT	src-tauri/src/spectrum.rs
Network + ICY demux, byte cursors	src-tauri/src/stream.rs
ICY metadata codec (decode)	src-tauri/src/icy.rs
Live-edge drift control	src-tauri/src/sync.rs
cpal output	src-tauri/src/output.rs
Session orchestration	src-tauri/src/engine.rs
Tauri commands	src-tauri/src/lib.rs

Controls

Action	Control
Play / pause	Play button, or Space
Stop	Stop button
Mute	Mute button, or M
Volume	Horizontal fader (drag, arrows, double-click to reset)
EQ band / preamp	Vertical faders (drag, arrows, double-click to 0 dB)
Presets	Flat / Pirate / Bass / Voice chips
Change station	Type a URL → Tune (or Enter)

Development

Prerequisites: Rust, Node 18+, and the Tauri system dependencies for your OS (Linux/macOS/Windows guide). On Debian/Ubuntu:

sudo apt-get install libwebkit2gtk-4.1-dev librsvg2-dev patchelf libasound2-dev

Then:

npm install
npm run tauri dev      # run in development
npm run tauri build    # produce a local installer bundle

Releases

Pushing a version tag builds installers for all three platforms via GitHub Actions (.github/workflows/release.yml) and attaches them to a draft Release:

git tag v0.1.0
git push origin v0.1.0

Produced artifacts: .dmg (macOS, Intel + Apple Silicon), .msi and NSIS .exe (Windows), and .AppImage / .deb / .rpm (Linux).

Automatic updates

The Receiver updates itself. Shortly after every start it checks the signed update manifest at https://www.ltbr.fm/api/player/updater (a cached proxy of the latest.json that the release workflow attaches to each GitHub release) and, when a newer version exists, downloads it, verifies the minisign signature against the public key embedded in tauri.conf.json, installs it in place, and restarts — showing a progress overlay while it happens. No clicks required; a failed check or download is silent and the current version keeps playing (re-checked every 4 hours).

This works everywhere the installation can replace itself: macOS .app, the Windows installers, and Linux AppImage. On .deb/.rpm installs the package manager owns the files, so those keep the passive behavior: the front-panel indicator lights up when a new version exists and clicking it opens the download page.

Release requirements: the TAURI_SIGNING_PRIVATE_KEY and TAURI_SIGNING_PRIVATE_KEY_PASSWORD repository secrets must hold the minisign key matching the plugins.updater.pubkey in tauri.conf.json — the private key lives outside the repository and must never be committed. Losing it means shipped apps can no longer verify (and therefore install) any future update.

Code signing

Binaries are unsigned by default, which triggers OS warnings on first launch of each version:

• macOS (Sequoia and later) reports unsigned downloads as "damaged and can't be opened" — nothing is damaged; it's Gatekeeper's verdict for unsigned internet downloads, and the old right-click → Open workaround no longer applies. After dragging the app to Applications, clear the quarantine flag once per update:

  xattr -cr "/Applications/LTBR FM Receiver.app"

• Windows: SmartScreen → "More info" → "Run anyway".

To remove the warnings permanently, sign & notarize: add the documented secrets (APPLE_* for macOS — requires an Apple Developer account — and a Windows Authenticode certificate) referenced in the release workflow; no workflow changes are required.

License

MIT — see LICENSE.