Audited my own docs for the Decoder's method-versus-subject error -- a negative
about the instrument written as a negative about the subject. Clean: every
impossibility claim in DECISIONS is already method-scoped ('undecodable WITH
REACH', 'cannot be answered BY LISTENING'), and both live open rows in BLOCKED
read 'not observed' and 'deliberately not inferred'. Nothing to fix, recorded as a
negative.
Then three cheap measurements located the fidelity fault exactly. Identity --
source against a second decode of itself at lag 0 -- subtracts to -inf, so
decode-and-subtract is exact and the pipeline was never the problem. A LOSSLESS
flac of the identical fold reaches only 14.2 dB down, searched exhaustively at
stride 1 over 300 lags, where it must reach about 90. The shipped transcode's 8.73
dB is therefore meaningless.
So the difference path is disqualified rather than inconclusive, and every number
it produced in this thread -- including the 'difference louder than source'
readings I reported twice -- was an artefact of the lag search, not evidence about
a transcode. The tool now refuses on that path and carries its acceptance test in
the code: make lossless-vs-source return >= 60 dB down before believing anything
it says.
The identity test costs one decode and no encoder, and it should have been the
first thing run three iterations ago. Before asking whether an instrument can
measure a difference, ask whether it returns zero for no difference.
Hypotheses ruled out and recorded so nobody re-runs them: drift (offset stable at
about -2465 samples across t=2, 10 and 20 s), container start time (start_time is
exactly 0), the codec being perceptual (the lossless control fails the same way),
and level or content mismatch (bands agree to 0.66 dB).
P4's waveform question is now open with a disqualified instrument -- worse than it
looked yesterday, and better than believing 8.73 dB meant something. The band
check is unaffected and still asserts.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N7FiFFFwbvG2uxdcEh8HyF
66fb49dba3