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

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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
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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](intro-audio-output-census.md) against that track and
solving `capture = g × movie + residual`
([`../data/intro-audio-decomposition.txt`](../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`](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`](intro-audio-output-census.md) labelled its channels
using the permutation `[0,1,4,5,2,3]` that
[`audio-capture-alsa-file-tee.md`](../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.