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
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sylph-decoder
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docs/re/data/intro-audio-channel-census.txt
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docs/re/data/intro-audio-channel-census.txt
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# The game's own audio output over the boot intro (Q9/#4 groundwork).
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#
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# 2026-08-30. Recipe: docs/re/audio-capture-alsa-file-tee.md, exactly.
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# ARGV: run-canary --apu=alsa --mute=false --gpu=null --xma_param_probe=true
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# ALSA file tee in front of a paced pulse slave; 6ch float32 @ 48 kHz.
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# Raw is 170 MB and is NOT committed -- sent via share.
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#
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# PROVENANCE (better than a screenshot for an audio question): the XMA probe
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# logged ADV's three contexts byte-exact against the disc --
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# ctx0 packets=632 byte_size=1294336
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# ctx1 packets=546 byte_size=1118208
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# ctx2 packets=572 byte_size=1171456
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# then two more (1150976 / 1269760) = the documented BGM_102 pair.
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#
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# CAPTURE QUALITY: 0.15-0.16 % silence on five channels, against the
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# 0.31 % the recipe page records for its clean --gpu=null run.
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#
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# ALSA CHANNEL ORDER: captured i holds source [0,1,4,5,2,3], i.e. the
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# labels below are FL FR BL BR FC LFE. Deterministic, not data loss.
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#
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frames 7105024 = 148.02 s, 6ch float32 @ 48 kHz
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ch name peak dBFS rms dBFS %silent
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0 FL -3.65 -22.26 0.16
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1 FR -2.22 -20.89 0.15
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2 BL -4.41 -24.77 0.15
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3 BR -11.65 -36.06 82.18
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4 FC -4.57 -24.81 0.16
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5 LFE -4.66 -24.38 0.16
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pairwise |r| > 0.5:
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ch0(FL) vs ch1(FR): r=+0.6996
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ch0(FL) vs ch4(FC): r=+0.5202
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ch1(FR) vs ch5(LFE): r=+0.5639
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docs/re/structures/intro-audio-output-census.md
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docs/re/structures/intro-audio-output-census.md
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# What the game actually emits over the boot intro — five live channels, not a stereo mix
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**Classification: measured.** Xenia Canary, 2026-08-30, one boot, no input.
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Groundwork for the port's ask #4 — **it does not settle #4**, and the part it does
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not settle is named at the bottom.
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## Why this capture exists
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The port ships one of `ADV`'s three concurrent voice streams and its
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`authored/audio.json` records that as **known wrong, held deliberately**
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([`voice-three-streams-are-concurrent.md`](voice-three-streams-are-concurrent.md)).
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Neither "take one" nor "sum them" is established. The only thing that can settle it
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is what the game emits, so: record it.
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## The capture
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Recipe followed exactly from
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[`audio-capture-alsa-file-tee.md`](../audio-capture-alsa-file-tee.md) — ALSA `file`
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tee in front of a **paced** pulse slave, `--gpu=null`, both mutes off:
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```
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run-canary --apu=alsa --mute=false --gpu=null --xma_param_probe=true
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```
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**148.02 s, 6 channels, float32, 48 kHz.**
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✅ **Provenance is the XMA probe, not a screenshot** — which is the right evidence
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for an audio question, because it witnesses the thing being recorded. The log
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carries `ADV`'s three contexts **byte-exact** against the disc:
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| ctx | packets | `byte_size` |
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|---|---|---|
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| 0 | 632 | 1 294 336 |
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| 1 | 546 | 1 118 208 |
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| 2 | 572 | 1 171 456 |
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then two more — 1 150 976 / 1 269 760 — which are the documented `BGM_102` pair.
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So the movie's voice decoded exactly as in the runs this corpus already records.
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✅ **Capture quality: 0.15–0.16 % silence** on the five live channels, against the
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**0.31 %** the recipe page records for its own clean run. Cleaner than the reference.
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## What is in the six channels
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⚠️ ALSA's channel order, not WAV's: captured *i* holds source `[0,1,4,5,2,3]`, so
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the labels below are `FL FR BL BR FC LFE`. Deterministic and invertible.
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| ch | | peak dBFS | rms dBFS | % silent |
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|---|---|---|---|---|
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| 0 | FL | −3.65 | −22.26 | 0.16 |
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| 1 | FR | −2.22 | −20.89 | 0.15 |
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| 2 | BL | −4.41 | −24.77 | 0.15 |
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| **3** | **BR** | **−11.65** | **−36.06** | **82.18** |
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| 4 | FC | −4.57 | −24.81 | 0.16 |
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| 5 | LFE | −4.66 | −24.38 | 0.16 |
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**Five channels carry real, distinct content; one (BR) is 82 % silent and 11–15 dB
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down.** No channel is a copy of another — the largest pairwise correlation is 0.70
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(FL/FR, which is what a stereo pair looks like), then 0.52 and 0.56.
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### 🔴 What this already rules out
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* **Not a stereo mix.** Five independent channels are being emitted.
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* **So "ship one stream" cannot be right**, which the corpus already suspected but
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had not observed from the output side. The port's held-wrong value stays wrong.
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⚠️ **It does not follow that summing is right.** This says the *output* is
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multichannel; it says nothing yet about which disc stream lands where.
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⚠️ **And do not read the 6 channels as proof the game is 5.1.** `CONTAINER-NOTES`
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records that `AudioDriver::kFrameChannelsDefault = 6` is a hardcoded Xenia
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constant — the *format* is Xenia's, only the *content* is the guest's. What is
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evidence here is that five of those six differ from each other, which a stereo
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guest cannot produce.
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## 🟡 What is NOT settled — the stream → channel mapping
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The decisive step is a cross-correlation of each captured channel against each of
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`ADV`'s three decoded streams. **That has not been run.** Until it is:
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* which stream feeds which channel pair is unknown;
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* whether `FC` carries the dialogue is **consistent with** the corpus's
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[centre-channel finding](../structures/voice-centre-channel.md) but not
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re-established here;
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* why `BR` is near-silent is unknown — a genuinely unused channel, a stream that
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ends early, or a decode that failed are all open.
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⚠️ **One boot, one movie.** And `--gpu=null` means no video, so nothing here is
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cross-checked against what was on screen.
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The raw capture is 170 MB and is **not committed**; it went over `share` to the
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port as `1788077587-9f2e30af1c98-capture.raw`. Per-channel numbers:
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[`../data/intro-audio-channel-census.txt`](../data/intro-audio-channel-census.txt).
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