# ✅ 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 assignment is now determined** — see the section below. It was open when
this page was first written.
⚠️ `--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.


## ✅ Which stream is which (2026-08-30, later)

The three chunks were dumped from the resolved voice region
(`examples/adv_voice_dump.rs`) and decoded:
[`../data/adv-stream-assignment.txt`](../data/adv-stream-assignment.txt).

| chunk | `byte_size` | probe ctx | L rms | R rms | R silent |
|---|---|---|---|---|---|
| 0 | 806 912 | **ctx0, clipped tail** (full 1 294 336) | −24.79 | −24.81 | 53.1 % |
| 1 | 1 118 208 | ctx1 | −20.33 | **−inf** | **100 %** |
| 2 | 1 171 456 | ctx2 | −30.67 | −30.68 | 53.6 % |

### 🔴 Two instruments failed first, and both look convincing

* **Envelope correlation cannot discriminate *here*.** A per-pair lag search returns
  **0.86–0.95 for every chunk against every channel**, because all six residual
  channels share the dialogue's activity timing. A number that high reads as a
  result; it is the instrument having no resolving power **in this regime**.
  ⚠️ **Corrected 2026-08-30 — do not generalise this.** The port agent controlled
  the same estimator on a single dialogue track and got **r = 1.0000 at zero offset
  and −0.08…+0.08 everywhere else**: it localises sharply. The saturation here is
  specific to **concurrent streams sharing timing at zero lag**, which a lag search
  over one track never encounters. This page said it flatly for a day after that
  correction was known, which is the failure `METHOD.md` calls *a correction that
  does not reach the artifact*.
* **Sample-level correlation returns ≈ 0.** The chunks do not start with the movie
  and the XMA decode's framing offset is unknown.

### ✅ Level settles it, under the same 0.600 gain

| chunk | level | × 0.600 | nearest residuals (error, dB) |
|---|---|---|---|
| 0L | −24.79 | −29.23 | **FL 0.05** · FR 0.06 · FC 3.96 |
| 1L | −20.33 | −24.77 | **FC 0.50** · FL 4.51 |
| 2L | −30.67 | −35.11 | **BL 0.35** · BR 0.38 · FR 5.82 |

Each stream lands within **0.5 dB** of exactly one residual pair and misses the
others by ~4–6 dB. **The same 0.600 that scales the movie bed also scales the
voice** — which is itself worth having: it is one mixer gain, not two.

✅ **Ratio test, immune to chunk 0 being clipped:** chunk0 − chunk2 = **+5.88 dB**
against FL − BL = **+6.18 dB**, agreeing to **0.30 dB**; swapped, the ratio would be
wrong by **11.76 dB**.

✅ **Structural confirmation.** Chunk 1 is the *only* chunk with a digitally silent
channel, and LFE is the *only* output channel with an empty residual (−115.73 dBFS).
One to one. And the internal L/R correlations track: chunk 0 **+0.932** against the
FL/FR residual's **+0.918**, chunk 2 **+0.962** against BL/BR's **+0.929**.

| stream | → |
|---|---|
| ctx0 · 1 294 336 | **FL, FR** |
| ctx1 · 1 118 208 | **FC** (LFE silent) |
| ctx2 · 1 171 456 | **BL, BR** |

🔴 **And the identifier this is indexed by does not resolve against the disc.** The
port refused to apply this assignment because the three contexts sum to 3 584 000 B
against a resolved region of 3 114 352. It was right to: the **region start is
wrong**, by 238 packets for `ADV` and on 8 of 10 multichannel regions disc-wide —
[`voice-region-starts-late.md`](voice-region-starts-late.md). The assignment above
still stands (the ratio test was chosen to be immune to the clipping), but chunk 0's
absolute level was measured over 62 % of its stream.

⚠️ **Reach.** Levels, not waveforms — this is an argument from three numbers
agreeing to 0.5 dB and a 1:1 structural match, not from a matched waveform. One
movie, one boot. And chunk 0 is a clipped tail, which is why the ratio test is
quoted alongside the absolute match.