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sylph-decoder 232ae0fa9c re: ask #4 answered -- the intro is a 5.1 WMAPro bed at 0.600 plus three streams

ADV.wmv carries ONE audio stream and it is wmapro 5.1, not XMA. Any framing of
the intro's audio as only 'which of three voice streams to ship' was missing the
bed.

Aligned the 148 s capture against that track (envelope r 0.769 against a median
of -0.001, refined to +224 samples, r 0.900) and solved
capture = g x movie + residual per channel.

The gain is 0.600 on every channel -- a uniform -4.44 dB, a mixer setting rather
than a fit artefact. LFE reproduces to -115.73 dBFS, 72 dB down, which is what
rules out codec difference as the explanation for the other residuals. FC is the
exception: the movie explains NOTHING of it (-0.09 dB), and the movie's own FC is
91.6 % silent.

The residual is three signals, not one: a front pair (r 0.918), a rear pair
(r 0.929), and a centre whose partner LFE is empty. The FC residual spans 34 dB
across 100 ms frames -- bursty, not steady noise.

That CONFIRMS the corpus's 5.1 reading, which voice-three-streams-are-concurrent
recorded as not established, and it confirms the specific detail it offered: that
the mono-in-stereo stream is 'a centre paired with a silent LFE'. Measured from
the output with no access to the stream contents.

Also corrects my own census page: it labelled channels with the ALSA permutation
[0,1,4,5,2,3] from the recipe page, which does NOT apply to this capture. The
6x6 matrix was computed assuming no order, every row's max falls on a distinct
movie channel, and the answer is the identity -- so the census's 'BR is 82 %
silent' was really LFE, reconciling with the movie's own 80.64 % silent LFE.

Reach: one boot, one movie; which XMA context is front/centre/rear is not
determined, only that the residual occupies those positions; and whether 0.600 is
a fixed constant or a volume setting is unknown.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wuu56cE8vJGTBtn1ppsk8v

2026-08-30 08:19:03 +00:00

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✅ The boot intro's audio: the movie's own 5.1 bed at 0.600, plus three streams in 5.1

Classification: measured. Xenia Canary, 2026-08-30, one boot, no input. This settles the port's ask #4 and confirms the corpus's leading hypothesis from the output side, where it had been recorded as "not established".

🔴 First: `ADV.wmv` is not three XMA streams. It is one WMA Pro 5.1 track.

ffprobe /disc/dat/movie/ADV.wmv
  Stream #0:0(jpn): Audio: wmapro, 48000 Hz, 5.1, fltp, 384 kb/s
  Stream #0:1(jpn): Video: wmv3, 1280x720, 30 fps

One audio stream, 5.1, decoded by Xenia's WMA path — not the XMA path the three probe contexts come from. Any framing of the intro's audio as only "which of three voice streams to ship" was missing the bed entirely.

The decomposition

Aligning the 148 s capture against that track and solving capture = g × movie + residual (../data/intro-audio-decomposition.txt):

ch	gain	r	capture rms	residual rms	residual/capture
FL	0.600	+0.905	−21.86	−29.28	−7.43 dB
FR	0.600	+0.935	−20.28	−29.29	−9.02 dB
FC	0.597	+0.146	−25.18	−25.27	−0.09 dB
LFE	0.600	+1.000	−43.66	−115.73	−72.06 dB
BL	0.600	+0.956	−24.89	−35.46	−10.58 dB
BR	0.600	+0.964	−24.02	−35.49	−11.47 dB

The gain is 0.600 on every channel — a uniform −4.44 dB, which is a mixer setting, not a fit artefact. LFE is reproduced to −115.73 dBFS, 72 dB below the signal: at that residual the two decoders agree essentially exactly, which is what rules out "the leftovers are just codec differences".

🔴 And FC is the exception that carries the answer. The movie explains nothing of the capture's centre channel — the residual is the whole signal (−0.09 dB). The movie's own FC is 91.6 % silent; the capture's is not.

The residual is three signals, not one

	FL	FR	FC	LFE	BL	BR
FL	1.000	0.918	0.017	0.001	0.009	0.004
FR	0.918	1.000	0.034	0.001	0.015	0.014
FC	0.017	0.034	1.000	0.000	0.385	0.378
LFE	0.001	0.001	0.000	1.000	0.000	−0.000
BL	0.009	0.015	0.385	0.000	1.000	0.929
BR	0.004	0.014	0.378	−0.000	0.929	1.000

Three coherent groups: a front pair (0.918), a rear pair (0.929), and a centre whose partner LFE is empty. The FC residual's 100 ms frame levels span 34 dB (median −53.9, p90 −19.9) — bursty, not steady noise.

✅ This confirms the 5.1 hypothesis, and predicts the silent channel correctly

voice-three-streams-are-concurrent.md recorded "three concurrent stereo streams is six channels" as the obvious reading and marked it not established, with a specific piece of supporting detail: that ADV stream 2 is mono-in-stereo, "a centre paired with a silent LFE looks exactly like that".

That is exactly what the residual shows — a live centre whose paired channel is empty to −115 dB. Measured from the output, with no access to the stream contents:

XMA stream	lands in
one	FL, FR
one	FC, LFE silent
one	BL, BR

So both things are true and the port needs both: the movie's own 5.1 WMA Pro track and the three streams mixed over it in 5.1.

🔴 Correction to the census page, and to the recipe page's channel order

intro-audio-output-census.md labelled its channels using the permutation [0,1,4,5,2,3] that audio-capture-alsa-file-tee.md records for ALSA. That permutation does not apply to this capture. The 6×6 correlation matrix was computed without assuming any order, every row's maximum falls on a distinct movie channel, and the result is the identity.

So the census's "BR is 82 % silent" was really LFE — which also reconciles it with the movie, whose LFE is 80.64 % silent. ⚠️ The recipe page's permutation was measured on a different chain and is not wrong there; what is wrong is assuming it travels. Measure the channel order per capture; a 6×6 matrix that comes out a clean permutation is its own control.

Reach

⚠️ One boot, one movie. ADV only. ⚠️ The stream→channel assignment is by position, not by content. Which of the three XMA contexts is the front, centre or rear stream is not determined here — that needs the streams decoded and correlated individually, which was not done. ⚠️ --gpu=null, so no video cross-check. ✅ The 0.600 gain is measured on this run; whether it is a fixed mix constant or a volume setting is not established.

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