Add experimental single-sideband and vestigial-sideband stereo encoding
modes alongside the standard DSB-SC stereo subcarrier path.
- add encoder mode selection (DSB, SSB, VSB)
- add Hilbert-transform based quadrature path for SSB generation
- add vestigial split with low-band DSB and high-band SSB handling
- wire the mode through config, control, engine, generator, and fmrtx
- add test coverage for the SSB path
The default mode remains the standard DSB stereo encoder.
Improve reliability in two critical paths:
- make config saves atomic by writing to a temp file in the target directory, syncing it, and renaming it into place so crashes cannot leave a half-written JSON config behind
- serialize runtime state transitions with a dedicated mutex so concurrent state updates from run() and writerLoop() cannot double-record transitions or increment counters twice
Also remove an unreachable nil-check after cloneFrame() to keep the engine loop honest and easier to reason about.
Wire tone frequency, tone amplitude, and audio gain through the live control path so the UI's live-update behavior matches the engine.
This changes the generator live params to carry tone and gain values, propagates them through Engine.UpdateConfig and txBridge.UpdateConfig, and extends the control-plane patch types accordingly.
It also refines the control API behavior:
- avoid holding the server config mutex across tx.UpdateConfig()
- report live=true only when a request contains at least one genuinely live-applicable field
Together these fixes align the UI semantics with the actual runtime behavior and remove a lock hazard in the config update path.
Rework the DSP chain to a clip-filter-clip architecture with cascaded 14 kHz low-pass stages, double 19/57 kHz protection notches, fixed pilot/RDS injection semantics, and explicit MPX gain calibration support. Update config defaults and tests to match the new broadcast-style modulation budgeting and protected composite path.
Add a lock-free stdin PCM ingest path, streaming resampler, stereo-linked limiting and pre-MPX audio filtering, plus the engine/control wiring needed to drive live audio into TX mode. Also document the ingest API and include a helper batch script for piping ffmpeg audio into fmrtx.
All major TX parameters are now hot-swappable during transmission:
- DSP params (drive, stereo, pilot, RDS levels, limiter) via
atomic.Pointer[LiveParams], loaded once per chunk (~50ms)
- RDS text (PS, RT) via atomic.Value in encoder, applied at
RDS group boundaries (~88ms)
- TX frequency via driver.Tune(), applied between chunks
Zero locks in DSP path. HTTP handler writes atomics, run loop
reads them. Validation happens before store.
New: SoapyDriver.Tune() for live frequency changes.
New: LiveConfigUpdate/LivePatch types for type-safe patching.
New: 4 engine tests for live DSP/freq/RDS updates + validation.
Keep frame sequence numbers monotonic, lock the RDS carrier to the exact pilot phase used by the stereo encoder, and apply the accompanying DSP/control cleanups needed for stable live transmission behaviour.
Keep DSP state persistent across generated frames, move the RDS encoder to arbitrary sample-rate operation, and tune the Pluto profile to the working 2.28 MHz path with the levels that finally decode reliably.
Introduce CLI TX mode, hardware driver selection, IQ resampling to device rate, and platform-specific PlutoSDR/SoapySDR integrations. Update engine pacing for blocking hardware writes and refresh docs/release notes for the hardware-ready v0.6.0-pre milestone.
Jan
