re: the boot intro's audio output -- five live channels, not a stereo mix

Groundwork for the port's ask #4; it does not settle #4.

Captured the game's own output over the boot intro following the ALSA file-tee
recipe exactly -- paced pulse slave, --gpu=null, both mutes off. 148.02 s, 6ch
float32 48 kHz, 0.15-0.16 % silence against the 0.31 % the recipe page records
for its own clean run.

Provenance is the XMA probe rather than a screenshot, which is the right evidence
for an audio question: ADV's three contexts appear byte-exact (1294336 /
1118208 / 1171456), then the documented BGM_102 pair.

Five of the six channels carry distinct content; BR is 82 % silent and 11-15 dB
down. No channel is a copy of another -- the largest pairwise correlation is 0.70
between FL and FR.

That rules out a stereo mix, so 'ship one stream' cannot be right and the port's
held-wrong value stays wrong. It does NOT establish that summing is right, and
the 6-channel count is Xenia's hardcoded kFrameChannelsDefault -- what is
evidence is that five of them differ, which a stereo guest cannot produce.

NOT settled and named as such: the stream-to-channel mapping. The
cross-correlation of each captured channel against each decoded ADV stream has
not been run. One boot, one movie, and --gpu=null means no video cross-check.

Raw is 170 MB and is not committed; sent over share to the port.

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

docs/re/structures/intro-audio-output-census.md

@@ -0,0 +1,93 @@
+# What the game actually emits over the boot intro — five live channels, not a stereo mix
+
+**Classification: measured.** Xenia Canary, 2026-08-30, one boot, no input.
+Groundwork for the port's ask #4 — **it does not settle #4**, and the part it does
+not settle is named at the bottom.
+
+## Why this capture exists
+
+The port ships one of `ADV`'s three concurrent voice streams and its
+`authored/audio.json` records that as **known wrong, held deliberately**
+([`voice-three-streams-are-concurrent.md`](voice-three-streams-are-concurrent.md)).
+Neither "take one" nor "sum them" is established. The only thing that can settle it
+is what the game emits, so: record it.
+
+## The capture
+
+Recipe followed exactly from
+[`audio-capture-alsa-file-tee.md`](../audio-capture-alsa-file-tee.md) — ALSA `file`
+tee in front of a **paced** pulse slave, `--gpu=null`, both mutes off:
+
+```
+run-canary --apu=alsa --mute=false --gpu=null --xma_param_probe=true
+```
+
+**148.02 s, 6 channels, float32, 48 kHz.**
+
+✅ **Provenance is the XMA probe, not a screenshot** — which is the right evidence
+for an audio question, because it witnesses the thing being recorded. The log
+carries `ADV`'s three contexts **byte-exact** against the disc:
+
+| ctx | packets | `byte_size` |
+|---|---|---|
+| 0 | 632 | 1 294 336 |
+| 1 | 546 | 1 118 208 |
+| 2 | 572 | 1 171 456 |
+
+then two more — 1 150 976 / 1 269 760 — which are the documented `BGM_102` pair.
+So the movie's voice decoded exactly as in the runs this corpus already records.
+
+✅ **Capture quality: 0.15–0.16 % silence** on the five live channels, against the
+**0.31 %** the recipe page records for its own clean run. Cleaner than the reference.
+
+## What is in the six channels
+
+⚠️ ALSA's channel order, not WAV's: captured *i* holds source `[0,1,4,5,2,3]`, so
+the labels below are `FL FR BL BR FC LFE`. Deterministic and invertible.
+
+| ch | | peak dBFS | rms dBFS | % silent |
+|---|---|---|---|---|
+| 0 | FL | −3.65 | −22.26 | 0.16 |
+| 1 | FR | −2.22 | −20.89 | 0.15 |
+| 2 | BL | −4.41 | −24.77 | 0.15 |
+| **3** | **BR** | **−11.65** | **−36.06** | **82.18** |
+| 4 | FC | −4.57 | −24.81 | 0.16 |
+| 5 | LFE | −4.66 | −24.38 | 0.16 |
+
+**Five channels carry real, distinct content; one (BR) is 82 % silent and 11–15 dB
+down.** No channel is a copy of another — the largest pairwise correlation is 0.70
+(FL/FR, which is what a stereo pair looks like), then 0.52 and 0.56.
+
+### 🔴 What this already rules out
+
+* **Not a stereo mix.** Five independent channels are being emitted.
+* **So "ship one stream" cannot be right**, which the corpus already suspected but
+  had not observed from the output side. The port's held-wrong value stays wrong.
+
+⚠️ **It does not follow that summing is right.** This says the *output* is
+multichannel; it says nothing yet about which disc stream lands where.
+
+⚠️ **And do not read the 6 channels as proof the game is 5.1.** `CONTAINER-NOTES`
+records that `AudioDriver::kFrameChannelsDefault = 6` is a hardcoded Xenia
+constant — the *format* is Xenia's, only the *content* is the guest's. What is
+evidence here is that five of those six differ from each other, which a stereo
+guest cannot produce.
+
+## 🟡 What is NOT settled — the stream → channel mapping
+
+The decisive step is a cross-correlation of each captured channel against each of
+`ADV`'s three decoded streams. **That has not been run.** Until it is:
+
+* which stream feeds which channel pair is unknown;
+* whether `FC` carries the dialogue is **consistent with** the corpus's
+  [centre-channel finding](../structures/voice-centre-channel.md) but not
+  re-established here;
+* why `BR` is near-silent is unknown — a genuinely unused channel, a stream that
+  ends early, or a decode that failed are all open.
+
+⚠️ **One boot, one movie.** And `--gpu=null` means no video, so nothing here is
+cross-checked against what was on screen.
+
+The raw capture is 170 MB and is **not committed**; it went over `share` to the
+port as `1788077587-9f2e30af1c98-capture.raw`. Per-channel numbers:
+[`../data/intro-audio-channel-census.txt`](../data/intro-audio-channel-census.txt).