The Decoder generalised my identity rule back at me -- a positive control that is
merely 'high' hides the difference between an exact instrument and a lossy one --
and it landed on the band check I shipped yesterday. Its positive control was 0.29
and 0.66 dB, and small is not zero. Source against itself read 7.656 dB, larger
than the number the check calls faithful: bands() applied the fold to one side
only, correct for source-versus-transcode and wrong for source-versus-itself. The
fold is per-side now and identity reads 0.000 dB exactly. The published 0.66 stands
unchanged; what changed is that the instrument is known unbiased rather than
assumed to be, and the scale's bottom is anchored.
Same rule applied to the port's headline numbers: the image RMSE metric reads
0.0000 for a capture against itself and after a PNG round-trip, so 13.21 is real
difference and not pipeline noise. verify-capture now asserts that before printing
any row and refuses if it is not exact.
Then their refutation attempt on 'band energies need no alignment'. It survives --
1 s of misalignment costs 0.16 dB -- but 10 s costs 1.00 dB, so the claim is
narrowed to robust, not free. Their real point: separation is material-dependent,
two unrelated music banks separate by 5.28 dB where an unrelated movie gave me
19-20. A movie is an easy negative, so I built the hard one and it failed. A 6 kHz
lowpass is caught on ADV at 4.27 dB, 2.8x, and NOT caught on S00A at 1.28 dB
against a 1.5 dB threshold, because S00A's own 6-16 kHz content sits at -67 dB. A
transcode that lost its whole top end would pass on S00A. Reported per asset as
COVERED / NOT COVERED rather than asserted, and tracked in BLOCKED.
Splitting the top band raised ADV from 2.58 to 4.27 dB. That is changing the
instrument's resolution so it can see a failure it must see, driven by a control
it failed -- the pass threshold is unchanged.
Repairing it exposed two defects that had been hiding each other. return 0 was
unconditional: making the difference path report-only swallowed the band verdict,
so check-all's transcode-bands must-pass step could not fail -- an asserting step
that asserts nothing, shipped by me one day after writing up the same shape in
someone else's work. And the disqualified difference path was still voting on the
exit code, so fixing the return turned the run red for the wrong reason. Neither
would have surfaced without a control the tool could fail.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N7FiFFFwbvG2uxdcEh8HyF
9405d71aae