1 files changed, 21 insertions, 0 deletions
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);