Add DSD (Digital Speech Decoder) support with mbelib WASM

[jLynx]

Description

This PR implements a full Digital Speech Decoder (DSD) stack to enable listening to digital voice protocols directly in the browser. It introduces a new dsd mode that supports FM-demodulated digital protocols, including DMR, P25 Phase 1, D-STAR, and NXDN.

To handle voice synthesis, the PR includes a WebAssembly (WASM) port of mbelib, allowing the decoding of AMBE and IMBE voice frames within the browser's performance constraints.

Core Changes

1. DSD DSP Pipeline

• Frame Sync: Implemented a robust sync detection engine using collapsed polarity matching for 24-dibit (DMR/P25/D-STAR) and 18-dibit (NXDN) sync words.
• Clock Recovery: Added a Mueller-Muller timing error detector to extract symbols from the 48 kHz IF stream.
• Adaptive Slicing: Implemented a 4-FSK slicer with exponential moving average (EMA) tracking of signal levels to handle variable signal strengths.
• Error Correction: Added ECC modules for Golay(24,12), Hamming(10,6,3), and Reed-Solomon GF(2^6) to improve decoding robustness.

2. mbelib WASM Integration

• Created a C wrapper for mbelib and an Emscripten-based build script (build.sh).
• Implemented a lazy-loading system in the Worker thread to initialize the WASM module only when needed.
• Added persistent heap buffers for zero-allocation decoding calls between JavaScript and WASM.

3. Protocol Support

• DMR: Support for Tier II voice superframes, including color code detection and TDMA slot-based muting.
• P25: Parsing of Network Access Codes (NAC) and Data Unit IDs (DUID), with support for LDU1/LDU2 voice units.
• NXDN & D-STAR: Basic voice deinterleaving and AMBE decoding.

4. UI & State Management

• Added a new dsd mode selector to the VFO panel.
• Implemented a real-time DSD status display (styled after SDR++ Brown) showing mode, sync status, talkgroups (TG), source IDs (SRC), and MBE error bars.

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How to Build mbelib (Prerequisite)

Since the mbelib.js and .wasm files are served from public/lib/, you must compile them once if they are missing:

cd mbelib-wasm
bash build.sh

Technical Notes

• Audio Sampling: The decoder emits 8 kHz audio frames, which are resampled to 48 kHz using a RationalResampler in the DSP worker to maintain compatibility with the existing audio pipeline.
• Performance: The DSP chain is highly optimized; most logic operates on dibit strings or integer arrays to minimize garbage collection overhead in the worker.

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	browsdr	feb08e4	Commit Preview URL Branch Preview URL	Apr 08 2026, 10:59 PM

[jLynx]

This is still a WIP and doesn't quite work correctly yet