gbozo/no-sdr v0.6.0

v0.6.0 — AM Stereo, Noise Reduction, ADPCM Compression

on GitHub

What's New

AM Stereo (C-QUAM) — Experimental

• Auto-detected in AM mode via two-stage verification: 25Hz Goertzel pilot detector + C-QUAM PLL lock confirmation
• When a C-QUAM station is detected, stereo decoding activates automatically — same UI flow as WFM stereo
• We need testers! ~45 US stations, a handful in Italy, Japan, Philippines, and Thailand still broadcast C-QUAM. Requires direct sampling mod or HF-capable dongle. Please report results via GitHub issues.

Noise Reduction

• Spectral NR — Wiener filter (512-pt FFT, overlap-add, minimum-statistics noise floor estimation). Has known artifacts on music/tonal signals — improvements planned.
• Noise Blanker — EMA amplitude tracking with 7-sample hang timer and smooth gain transitions. Works well for impulse noise on AM/HF.
• WFM Stereo Blend — SNR-proportional continuous blend (0–1) replaces hard stereo on/off. Weak stations fade gracefully to mono.

IMA-ADPCM Compression

• Per-client codec negotiation: none or adpcm for both FFT and IQ streams
• FFT ADPCM: ~8:1 compression (Float32 → Int16 dB×100 → 4-bit ADPCM + 10-sample warmup)
• IQ ADPCM: 4:1 compression (Int16 → 4-bit ADPCM)
• Default: ADPCM enabled for both FFT and IQ
• Live compression stats in the UI (wire bytes, ratio, savings)

Server Optimizations

• FFT rate cap — configurable fftFps per profile (default 30). All computed FFT frames averaged into pending frame, emitted at target rate. Reduces ~1172 fps → 30 fps.
• WebSocket backpressure — checks bufferedAmount before sending (256KB for FFT, 1MB for IQ). Slow clients get frames dropped with warning log.
• Audio-gated IQ — server only sends per-user IQ data after client sends audio_enabled command.

Dongle Hardware Configuration

• New config options: directSampling, biasT, digitalAgc, offsetTuning, ifGain, tunerBandwidth
• Full rtl_tcp protocol support (commands 0x01–0x0E)
• HF direct sampling dongle example in config.yaml

UI Improvements

• Classic analog S-meter (needle mode) with warm backlit face, dual scale, red needle, peak hold
• Stereo indicator and controls for both WFM and AM modes
• Waterfall resize preservation (offscreen canvas snapshot)
• Spectrum renderer 30fps throttle
• Compression stats panel with live ratio and savings display

Other

• Per-profile fftFps configuration (1–60, default 30)
• FFT size limit raised to 16384
• Dev scripts run shared/server/client in parallel with watch mode
• Stereo PLL stability: faster energy tracking, 200ms hold timer, wider BPF