Module downsample 

FT8-tuned wrapper around the generic downsampler in crate::core::dsp::downsample.

Keeps the pre-existing crate::ft8::downsample::{downsample, downsample_simple, build_fft_cache} signatures so existing callers (decode.rs, WASM glue, benchmarks) continue working without change. The heavy lifting lives in mfsk-core so FT4 and future LDPC-family modes reuse it.

Constants

FT8_CFG

FT8 downsample configuration: 12 kHz → 200 Hz, 8 tones spaced 6.25 Hz apart.

Functions

build_fft_cache

Compute only the forward FFT cache (192 000-point) — expensive, shared across all subsequent downsample calls for the same audio block.

downsample

Downconvert and decimate audio to a complex baseband at 200 Hz centred on f0. Matches the pre-refactor signature: returns the result plus the forward-FFT cache so candidate loops can avoid recomputing it.

downsample_simple

No-cache convenience: returns only the 3200-sample baseband.