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.h | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) create mode 100644 src/audio/ola.h (limited to 'src/audio/ola.h') diff --git a/src/audio/ola.h b/src/audio/ola.h new file mode 100644 index 0000000..3dbc368 --- /dev/null +++ b/src/audio/ola.h @@ -0,0 +1,21 @@ +// This file is part of the 64k demo project. +// Shared OLA encode/decode helpers (Hann analysis, rectangular synthesis). +// Used by spectool, tests, and any batch PCM<->spec conversion. + +#pragma once +#include "audio/dct.h" + +// Returns number of OLA frames for n_samples PCM input. +static inline int ola_num_frames(int n_samples) { + return (n_samples > DCT_SIZE) ? (n_samples - DCT_SIZE) / OLA_HOP_SIZE + 1 + : 1; +} + +// Hann-windowed FDCT with 50% overlap (analysis). +// spec must hold ola_num_frames(n_samples) * DCT_SIZE floats. +void ola_encode(const float* pcm, int n_samples, float* spec, int num_frames); + +// IDCT-OLA with rectangular synthesis window (no synthesis window). +// Hann at 50% overlap satisfies w[n]+w[n+H]=1 → perfect reconstruction. +// pcm must hold num_frames * OLA_HOP_SIZE floats. +void ola_decode(const float* spec, int num_frames, float* pcm); -- cgit v1.2.3