fix: classify companion cores on correlation alone #2

Merged

nugget merged 1 commit from fix/companion-core-noise-floor into main

2026-08-11 10:32:54 -05:00

claude commented

2026-08-11 10:31:36 -05:00

Collaborator

Found by running the tool against the Fellowship extended cut.

A TrueHD's AC-3 companion measured r=0.996 — higher than either dub control — but was classified as a foreign dub because its level in the film's quiet passages sat +2.4 dB above the main mix, outside the ±2 dB the rule allowed.

That lift is the companion's own quantisation noise floor, not added content. The window's quiet quartile was at −57 dB, where a 448 kbit AC-3's noise floor is relatively prominent; the same track measured +0.6 dB in a louder window and classified correctly.

Correlation is unaffected and separates the cases cleanly:

	correlation
companion cores	0.996–0.998
foreign dubs	0.908–0.952

So the companion is now decided on correlation alone, with the counter-example recorded in the code per AGENTS.md.

Found by running the tool against the Fellowship extended cut. A TrueHD's AC-3 companion measured `r=0.996` — higher than either dub control — but was classified as a foreign dub because its level in the film's quiet passages sat +2.4 dB above the main mix, outside the ±2 dB the rule allowed. That lift is the companion's own quantisation noise floor, not added content. The window's quiet quartile was at −57 dB, where a 448 kbit AC-3's noise floor is relatively prominent; the same track measured +0.6 dB in a louder window and classified correctly. Correlation is unaffected and separates the cases cleanly: | | correlation | |---|---| | companion cores | 0.996–0.998 | | foreign dubs | 0.908–0.952 | So the companion is now decided on correlation alone, with the counter-example recorded in the code per `AGENTS.md`.

claude added 1 commit

2026-08-11 10:31:36 -05:00

fix: classify companion cores on correlation alone 7682fd5049

A lossy companion track shows a small positive level lift in the film's
quiet passages -- that is its own quantisation noise floor, not added
content. The previous rule required the lift to be within 2 dB, which
misfiled a TrueHD's AC-3 companion as a foreign dub in a passage whose
quiet quartile sat at -57 dB. The same track measured +0.6 dB in a
louder window.

Correlation separates the two cleanly and is not affected: companions
measured 0.996-0.998 against dubs at 0.908-0.952.