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- spectool --wav <input.spec> <output.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 <noreply@anthropic.com>
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Add v2 spectrogram format (SPEC_VERSION_V2_OLA) using overlap-add IDCT
with 50% overlap (hop=256, OLA_OVERLAP=256) and Hann windowing.
- dct.h: OLA_HOP_SIZE=256, OLA_OVERLAP=256
- synth.h: SPEC_VERSION_V1/V2_OLA constants; version field on Spectrogram
- window.h/cc: hann_window_512() alongside existing hamming_window_512()
- synth.cc: g_hann[] precomputed at init; OLA path in synth_render when
ola_mode=true (IDCT -> Hann -> add overlap tail -> save new tail ->
output OLA_HOP_SIZE samples); v1 path unchanged for backward compat
- tracker.cc: MP3 encoder now uses sliding 512-sample Hann window with
OLA_HOP_SIZE advance per frame; sets version=SPEC_VERSION_V2_OLA;
.spec files propagate header->version; generated notes stay v1
Existing .spec files must be regenerated to benefit from click-free OLA.
handoff(Claude): OLA done. .spec files need regen via MP3 tool to activate v2.
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This commit applies a new project-wide rule that every source file must begin with a concise 3-line comment header describing its purpose.
- Updated CONTRIBUTING.md with the new rule.
- Applied headers to all .cc and .h files in src/ and tools/.
- Fixed various minor compilation errors and missing includes discovered during the header update process.
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Adds a multi-voice, real-time audio synthesis engine that generates sound from spectrogram data using an Inverse Discrete Cosine Transform (IDCT).
Key features:
- A thread-safe, double-buffered system for dynamically updating spectrograms in real-time without interrupting audio playback.
- Core DSP components: FDCT, IDCT, and Hamming window functions.
- A simple sequencer in the main loop to demonstrate scripted audio events and dynamic updates.
- Unit tests for the new synth engine and Hamming window, integrated with CTest.
- A file documenting the build process, features, and how to run tests.
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