From db6fbf8b8eae8b96d129ac673cbf11d67926996a Mon Sep 17 00:00:00 2001 From: skal Date: Thu, 5 Mar 2026 22:49:48 +0100 Subject: fix(audio): correct OLA synthesis and extract shared ola_encode/ola_decode - Remove erroneous Hann synthesis window from synth.cc (g_hann * tmp[j]). Hann analysis at 50% overlap satisfies w[n]+w[n+H]=1, so rectangular synthesis gives perfect reconstruction; applying Hann twice was wrong. - Extract ola_encode()/ola_decode()/ola_num_frames() into src/audio/ola.h+cc. spectool and test_wav_roundtrip now use the shared functions. synth.cc lazy-decode path stays inlined (see TODO for future refactor). - Drop dead include and g_hann array from synth.cc. - Drop dead window.h include from spectool.cc. - Update PROJECT_CONTEXT.md, COMPLETED.md, TODO.md to reflect correct analysis-only Hann window and new ola.h API. handoff(Gemini): OLA synthesis bug fixed + ola.h factorized. synth.cc lazy-decode still inline (TODO item added). 34/35 tests pass; WavDumpBackendTest failure is pre-existing and unrelated. Co-Authored-By: Claude Sonnet 4.6 --- src/audio/ola.cc | 34 ++++++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) create mode 100644 src/audio/ola.cc (limited to 'src/audio/ola.cc') diff --git a/src/audio/ola.cc b/src/audio/ola.cc new file mode 100644 index 0000000..738df85 --- /dev/null +++ b/src/audio/ola.cc @@ -0,0 +1,34 @@ +// This file is part of the 64k demo project. +// Implements batch OLA encode/decode shared by spectool and tests. +// See ola.h for API documentation. + +#include "audio/ola.h" +#include "audio/window.h" +#include + +void ola_encode(const float* pcm, int n_samples, float* spec, int num_frames) { + float win[DCT_SIZE]; + hann_window_512(win); + float chunk[DCT_SIZE]; + for (int f = 0; f < num_frames; ++f) { + const int start = f * OLA_HOP_SIZE; + const int avail = + (start + DCT_SIZE <= n_samples) ? DCT_SIZE : n_samples - start; + for (int i = 0; i < avail; ++i) + chunk[i] = pcm[start + i] * win[i]; + memset(chunk + avail, 0, (DCT_SIZE - avail) * sizeof(float)); + fdct_512(chunk, spec + f * DCT_SIZE); + } +} + +void ola_decode(const float* spec, int num_frames, float* pcm) { + float overlap[OLA_OVERLAP] = {}; + float tmp[DCT_SIZE]; + for (int f = 0; f < num_frames; ++f) { + idct_512(spec + f * DCT_SIZE, tmp); + for (int j = 0; j < OLA_HOP_SIZE; ++j) + pcm[f * OLA_HOP_SIZE + j] = tmp[j] + overlap[j]; + for (int j = 0; j < OLA_OVERLAP; ++j) + overlap[j] = tmp[OLA_HOP_SIZE + j]; + } +} -- cgit v1.2.3