From 2f8926f433248af28081497e8371e02abe61d6ff Mon Sep 17 00:00:00 2001 From: skal Date: Thu, 5 Mar 2026 21:50:53 +0100 Subject: feat(spectool): add --wav decode, IMDCT, and roundtrip test MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit - spectool --wav : decodes .spec to mono 16-bit WAV at 32 kHz using IDCT-OLA synthesis (no synthesis window). The analysis Hann window at 50% overlap satisfies w[n]+w[n+H]=1, so the synthesis window must be rectangular for perfect reconstruction. - Add imdct_512 / imdct_fft to audio lib (fft.cc, fft.h, idct.cc, dct.h) for future MDCT-based synthesis. - test_wav_roundtrip: in-process OLA analyze+decode SNR test (≥30 dB). Currently measures 53 dB on a 440 Hz sine. - Fix stale test_spectool.cc: version assertion updated from 1 to SPEC_VERSION_V2_OLA (was always wrong since OLA fix landed). - Docs: TOOLS_REFERENCE.md removes dead specview, documents --wav / --normalize / test_gen. HOWTO.md adds decode section. TRACKER.md notes spec v2 OLA format and decode command. Co-Authored-By: Claude Sonnet 4.6 --- src/audio/fft.h | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'src/audio/fft.h') diff --git a/src/audio/fft.h b/src/audio/fft.h index 8c10afd..df37ad5 100644 --- a/src/audio/fft.h +++ b/src/audio/fft.h @@ -32,4 +32,11 @@ void dct_fft(const float* input, float* output, size_t N); // N must be a power of 2 void idct_fft(const float* input, float* output, size_t N); +// IMDCT via FFT +// Input: input[] (length N) — MDCT coefficients +// Output: output[] (length 2*N) — time-domain samples +// Window output with Hann(2N) and OLA with hop N for perfect reconstruction. +// N must be a power of 2 +void imdct_fft(const float* input, float* output, size_t N); + #endif /* AUDIO_FFT_H_ */ -- cgit v1.2.3