TrueHz synthetic AAC round-trip recipe — 19 September 2026

Requires macOS, Python 3.12 or newer, and Apple's built-in afconvert. No private repository
or Decaud source checkout is needed. These are synthetic-fixture generator
sources, not the player or classifier source.

From this extracted directory:
  python3 -m venv .venv
  .venv/bin/python -m pip install -r requirements.txt
  .venv/bin/python -c 'import generate; generate.generate_lossy_fixture("output")'
  .venv/bin/python test_generate.py

Import output/Vesper Kite/Slow Light (AAC round-trip fixture)/01 Slow Light
(AAC round-trip).flac into Decaud on a Mac. Run its TrueHz analysis and inspect
the report. Retain the adjacent encoding-manifest.json with your result.

The 30-second source combines seeded synthesized music (gain 0.7) and Gaussian
broadband noise (gain 0.12), clipped to [-1, 1], as stereo 16-bit/44.1 kHz PCM.
It then passes through AAC 64 kbps CBR at 44.1 kHz, PCM decode, and FLAC encode.
The fixture function always regenerates this output. It does not run the full
fictional music catalog. Intermediate WAV/AAC files are temporary; their hashes
and exact conversion commands are recorded in the manifest.

Reference check: macOS 27.0; Python 3.14; numpy 2.5.3, Pillow 12.3.0,
mutagen 1.48.1; development core a90c8c680f2243eb31bfbed32300ed0c59176f04.
The existing core probe returned Transcoded (FAKE@96), cutoff 12,438 Hz.
96 kbps is a spectral estimate, not the actual encoder setting (64 kbps).
This is a core-probe observation, not a verified 1.5.1 UI result.

reference-encoding-manifest.json records the checked file's hashes. Codec,
macOS and font changes can alter bytes; compare your own manifest and verdict.
The initial music-only AAC round trip (encoder-selected sample rate) passed as
Genuine. The final broadband
probe is a worked illustration, not a representative accuracy benchmark.
No verdict is embedded or forced by the generator.

The integration test verifies actual codecs, source reconstruction, final-file
hashes, regeneration, and that AAC changes the PCM while FLAC preserves decoded
PCM exactly. The commercial app is needed to check the TrueHz verdict.
