re: a bank's wave 1 is not a filtered copy of wave 0 -- and my own discriminator cannot finish the job

Coherence on BGM_103, the menu's bank, with controls run first: a real linear
filter of wave 0 reads 0.93-0.94 in every band, a different bank reads 0.001, and
wave 0 misaligned by 1 s reads 0.004-0.057. The measurement reads 0.027 at 1-4 kHz,
so the 'wave 1 is wave 0 filtered' model is refuted.

The frequency structure is inverted relative to any mic-pair or reverb model:
coherence rises with frequency (0.169 -> 0.827) while energy falls (71 % -> 0.2 %),
and a rear pair decorrelates fastest at HF. In the midrange the two waves are 13x
further apart than the two channels of one wave.

But the L-R control is what limits the tool and it is recorded as such: within one
wave, genuinely one performance in two channels, coherence is only 0.221-0.497. So
'same performance' does not imply high coherence here, my positive control was the
wrong model of the rear-pair reading, and the 🟡 is NOT settled. The tool tests for
linear filtering and neither surviving reading requires it.

Also corrects MISSION's Q10 row, which still carried the refuted three-sub-wave
premise and had directed work at a dead question for days. Its gate is in fact met.

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

docs/port/MISSION.md

@@ -74,7 +74,7 @@ alongside it.
 | **Q7** | **Transitions.** What happens visually between screens — the `pteff00.prm` quads, a fade, a cut — and its timing | Described and timed against a capture |
 | **Q8** | **Menu audio.** Which BGM per screen; which cue on move / confirm / back / error. The cue table is complete; the event binding is not | Cue names bound to events, with how you established each |
 | **Q9** | **Video binding.** Which movie is the boot intro vs the new-game intro; whether playback is skippable and what ends it | Named movies plus the playback rules |
-| **Q10** | **What are a music bank's sub-waves?** `BGM_001.slb` is three sub-waves — 10 KB, 4.47 MB, 4.67 MB — and we currently **concatenate them blindly** into one 347 s track. Two near-equal halves could be intro + loop, or two variations, or two halves of one piece. A menu that loops its music needs to know which | The role of each sub-wave, established for at least the menu BGM. "Concatenate" is a decision, not a default — right now it is a default nobody chose |
+| **Q10** | ~~**What are a music bank's sub-waves?**~~ ✅ **ANSWERED — see below.** Every factual premise in the original row is refuted: a bank is **two** waves, not three (the 10 KB was the bank *header*, emitted by our own reader), and the three candidate roles it listed — intro + loop, two variations, two halves — are all dead. | ✅ **Gate met.** Role established on the menu's own bank: [`bgm-two-stems.md`](../re/structures/bgm-two-stems.md). 🟡 One sub-question survives — *which kind* of second stem — and it is 🟡 by measurement, not by neglect |
 | **S1** | ~~**Ready Room probe.**~~ **DONE 2026-08-28 — [no-go](../re/ready-room-probe.md).** It is 2D and enumerates fine, but the pak is briefing/tactical-map content, not the Ready Room menu | ✅ go/no-go written |
 
 ## ✅ Emulator-side questions are NOT blocked — corrected 2026-08-30
@@ -290,6 +290,37 @@ What needs a decision is which way the divergence gets closed:
 
 Recorded rather than chosen, per "do not improvise around a blocker".
 
+## ✅ Q10 is answered — corrected 2026-08-30
+
+The Q10 row above was written on a premise that has since been **refuted in every
+part**, and it survived as a live question for days after the refutation landed.
+Recording the correction here rather than silently editing the row:
+
+* ❌ *"`BGM_001.slb` is three sub-waves (10 KB, 4.47 MB, 4.67 MB)"* — the 10 KB is
+  the **bank header**. Our reader emitted it, from a modulus valid only for a
+  header shorter than one XMA packet. A bank is **two** waves, **28/28** disc-wide.
+* ❌ *"we currently concatenate them blindly"* — and concatenating is **wrong**,
+  now measured: the two waves are **sample-synchronous** and the running game
+  decodes **both at once** (the XMA probe at the main menu saw two stereo streams
+  whose byte sizes are `BGM_103`'s two declared waves, exactly).
+* ❌ *"could be intro + loop, or two variations, or two halves of one piece"* — all
+  three predict unequal durations; **32 banks give equal ones**.
+* ✅ **The gate — "the role of each sub-wave, established for at least the menu
+  BGM" — is met**, and on the menu's own bank: `BGM_103`, named from the
+  executable, confirmed against the disc and against the running game.
+
+🟡 **What is still open is narrower than the row**: *which kind* of second stem —
+the rear pair of a 4-channel mix, or a second intensity layer. Both predict
+simultaneity, so runtime observation cannot separate them, and a coherence
+discriminator run 2026-08-30 **refuted the "filtered copy" model but could not
+separate the two** — its own control showed that in this material even L vs R of
+one performance reads only 0.22–0.50, so the test's premise does not hold.
+[`../re/data/bgm-stem-coherence.txt`](../re/data/bgm-stem-coherence.txt)
+
+⚠️ **This distinction does not block the port.** Both readings give the same
+instruction: play both waves, aligned at sample 0, together. It changes only how
+they would be *mixed* if the port ever does surround.
+
 ## Known unknowns — say so, do not fill them in
 
 Some of these may turn out to be undecodable. That is a valid, useful answer, and

docs/re/REFUTED.md

@@ -761,3 +761,31 @@ sweep phases — and the 350×396 logo ROI is **byte-identical across all of the
 (0 / 138 600 px differing, max |d| 0), reproduced in two independent sessions**,
 while 5–8 % of the whole frame moves as a contrast control. The sweep ink does
 not land on the logos. The ±1–2 residual is not sweep.
+
+### Music-bank stems (2026-08-30)
+
+* ~~"wave 1 is wave 0 put through a filter"~~ — ❌ **refuted** on `BGM_103` by
+  magnitude-squared coherence. A real linear filter of wave 0 reads **0.93–0.94**
+  in every band (positive control); the measurement reads **0.027** at 1–4 kHz.
+  No linear filter does that in a band where both waves carry energy.
+  [data](data/bgm-stem-coherence.txt)
+* ~~"the rear-pair reading can be tested by coherence"~~ — ❌ **refuted, and it was
+  my own test's premise.** The control that matters — L vs R *within* one wave,
+  genuinely one performance in two channels — reads only **0.221–0.497**, so in
+  this material "same performance" does not imply high coherence. A 4-channel
+  mix's rear pair is not a linear filter of its front pair, so the discriminator
+  never had the power to separate the two readings. The 🟡 stands.
+
+### Refutation attempt on the corpus's "two stems of ONE PERFORMANCE" — 🟡 SURVIVED, WEAKENED (2026-08-30)
+
+**Target:** `structures/bgm-two-stems.md` (the `BGM_103` section is another
+agent's), which reads the two waves as two stems *of one performance*.
+
+**My attempt:** if they are one performance, they should share signal structure;
+coherence should be well above the independent floor across the bands carrying
+the music.
+
+**Result: the claim survives, but one of its supporting readings is dead and the
+bands carrying 96 % of the energy read 0.169 and 0.184** — far above the 0.001
+independent floor, so *not* independent, and far below a filtered copy. "One
+performance" stands; "rear pair, i.e. a filtered view of the same mix" does not.

docs/re/data/bgm-stem-coherence.txt

@@ -0,0 +1,71 @@
+# Is a music bank's wave 1 the SAME instruments filtered, or DIFFERENT parts?
+# BGM_103 (the menu's music) -- 2026-08-30
+#
+# structures/bgm-two-stems.md leaves two readings alive for wave 1: the rear
+# pair of a 4-channel mix, or a second intensity layer -- and correctly notes
+# that runtime simultaneity cannot separate them, because both predict it.
+# This is a static attempt at a discriminator.
+#
+# METHOD: magnitude-squared coherence, Welch, NFFT 8192 @ 48 kHz, 60 s window
+# (702 segments, so the bias floor is ~1/702 = 0.0014). Coherence is ~1 wherever
+# one signal is a LINEAR FILTER of the other and ~0 for independent signals.
+# tools/re-capture/bgm_stem_coherence.py
+#
+# WAVES: slb_extract_wave.py BGM_103.slb 14336 1893 2 48000   (wave 0)
+#        slb_extract_wave.py BGM_103.slb 3903488 1919 2 48000 (wave 1)
+#        then ffmpeg -i x.riff x.wav. Both decode to 87.744 s, 4 211 729 frames.
+# CONTROL BANK: BGM_104.slb 14336 1305 (a different piece, same codec).
+#
+CONTROLS
+  POS w0 vs linear-filter(w0)        0-0.2k 0.929  0.2-1k 0.938  1-4k 0.936  4-12k 0.938  12-16k 0.938  16-24k 0.937
+  NEG w0 vs a different bank         0-0.2k 0.001  0.2-1k 0.001  1-4k 0.001  4-12k 0.001  12-16k 0.001  16-24k 0.002
+  NEG w0 vs w0 shifted 1 s           0-0.2k 0.057  0.2-1k 0.048  1-4k 0.007  4-12k 0.019  12-16k 0.015  16-24k 0.004
+  REF w0 L vs R (one perf.)          0-0.2k 0.321  0.2-1k 0.221  1-4k 0.363  4-12k 0.445  12-16k 0.497  16-24k 0.450
+  REF w1 L vs R (one perf.)          0-0.2k 0.078  0.2-1k 0.051  1-4k 0.089  4-12k 0.411  12-16k 0.453  16-24k 0.455
+
+MEASUREMENT
+  w0 vs w1                           0-0.2k 0.169  0.2-1k 0.184  1-4k 0.027  4-12k 0.635  12-16k 0.768  16-24k 0.827
+
+ENERGY SHARE
+  w0                                 0-0.2k  71.4%  0.2-1k  24.8%  1-4k   2.4%  4-12k   1.0%  12-16k   0.1%  16-24k   0.2%
+  w1                                 0-0.2k  53.8%  0.2-1k  40.9%  1-4k   2.3%  4-12k   2.1%  12-16k   0.3%  16-24k   0.6%
+
+# ------------------------------------------------------------------------------
+# READING IT
+#
+# ✅ THE INSTRUMENT IS CALIBRATED. A real linear filter of w0 reads 0.93-0.94 in
+# every band; a different bank reads 0.001-0.002; w0 against itself misaligned by
+# 1 s reads 0.004-0.057. So the estimator detects filtering and is not fooled by
+# two pieces of music in the same codec.
+#
+# ❌ REFUTED: "wave 1 is wave 0 put through a filter." The positive control says
+# a filter reads 0.936 at 1-4 kHz. The measurement reads 0.027 there. No linear
+# filter produces that in a band where both waves carry energy.
+#
+# 📌 THE FREQUENCY STRUCTURE IS INVERTED relative to any mic-pair or reverb
+# model. Coherence RISES with frequency -- 0.169, 0.184, 0.027, 0.635, 0.768,
+# 0.827 -- while energy FALLS -- 71.4 %, 24.8 %, 2.4 %, 1.0 %, 0.1 %, 0.2 %.
+# A rear pair or a reverb return decorrelates FASTEST at high frequency, which
+# is the opposite. What is coherent lives in bands holding ~1.3 % of the energy;
+# the bands holding 96 % of it read 0.169 and 0.184.
+#
+# 📌 AND IN THE MUSICAL MIDRANGE THE TWO WAVES ARE FURTHER APART THAN THE TWO
+# CHANNELS OF ONE WAVE: 1-4 kHz gives 0.027 between waves against 0.363 for w0's
+# own L vs R -- a factor of 13. Two channels of one performance agree far more
+# than the two waves do.
+#
+# 🔴 BUT THE L-R CONTROL IS ALSO WHAT LIMITS THIS TOOL, AND IT KILLS THE CLEAN
+# ANSWER. L vs R within a single wave is genuinely "one performance, two
+# channels", and it reads only 0.221-0.497 -- nowhere near the 0.94 a filter
+# gives. So in THIS material "same performance" does not imply high coherence,
+# which means my positive control was the wrong model of the rear-pair reading:
+# a real 4-channel mix's rear pair is not a linear filter of its front pair.
+#
+# => The filter model is dead. The two named readings are NOT separated. This
+#    tool cannot separate them, and the reason is stated rather than discovered
+#    later: it tests for linear filtering, and neither reading requires it.
+#
+# ⚠️ REACH: one bank (BGM_103), one 60 s window, mono-summed for the coherence
+# rows. Not run over the other 31 banks. The 16-24 kHz reading of 0.827 sits in
+# 0.2-0.6 % of the energy and is unexplained -- it is NOT generic codec
+# behaviour, since the different-bank control reads 0.002 in the same band.

docs/re/structures/bgm-two-stems.md

@@ -92,6 +92,47 @@ twice, the second time as a bass-less secondary stem.
   decorrelated between L and R, and with the bass managed away to the front pair.
 * **A second intensity layer** to be mixed in or crossfaded.
 
+### ❌ One of the two is now narrowed: wave 1 is NOT a filtered copy of wave 0
+
+**measured 2026-08-30** — [`../data/bgm-stem-coherence.txt`](../data/bgm-stem-coherence.txt),
+`tools/re-capture/bgm_stem_coherence.py`, on **`BGM_103`**, the menu's bank.
+
+Magnitude-squared coherence is ~1 wherever one signal is a **linear filter** of
+the other. Controlled first: a real filter of wave 0 reads **0.93–0.94** in every
+band, a different bank reads **0.001**, and wave 0 against itself misaligned by
+1 s reads **0.004–0.057**.
+
+| band | w0 vs w1 | w0's own L vs R | energy in w0 |
+|---|---|---|---|
+| 0–200 Hz | 0.169 | 0.321 | 71.4 % |
+| 200 Hz–1 kHz | 0.184 | 0.221 | 24.8 % |
+| **1–4 kHz** | **0.027** | **0.363** | 2.4 % |
+| 4–12 kHz | 0.635 | 0.445 | 1.0 % |
+| 16–24 kHz | 0.827 | 0.450 | 0.2 % |
+
+❌ **"Wave 1 is wave 0 filtered" is dead.** A filter reads 0.936 at 1–4 kHz; the
+measurement reads **0.027**.
+
+📌 **The frequency structure is inverted** relative to any mic-pair or reverb
+model: coherence *rises* with frequency while energy *falls*. A rear pair or a
+reverb return decorrelates fastest at HF. Whatever is coherent lives in bands
+holding ~1.3 % of the energy; the bands holding 96 % of it read 0.169 and 0.184.
+
+📌 **In the midrange the two waves are 13× further apart than the two channels of
+one wave** — 0.027 against 0.363.
+
+🔴 **But the same control kills the clean answer, so this does NOT settle the
+🟡.** L vs R *within* one wave is genuinely one performance in two channels, and
+it reads only **0.221–0.497** — nowhere near 0.94. So in this material "same
+performance" does not imply high coherence, and my positive control was the wrong
+model of the rear-pair reading: a real 4-channel mix's rear pair is not a linear
+filter of its front pair. **The tool tests for linear filtering, and neither
+surviving reading requires it.** Stated here rather than discovered later.
+
+⚠️ Reach: one bank, one 60 s window, mono-summed. The 16–24 kHz reading of 0.827
+is unexplained and is *not* generic codec behaviour — the different-bank control
+reads 0.002 in that same band.
+
 **Not settled, and the obvious field does not settle it.** `ChannelMask` is
 `0x0002` on *both* waves, and [`sound-slb.md`](sound-slb.md) already records that
 this game writes meaningless channel metadata (movie voices declare 2 channels

tools/re-capture/bgm_stem_coherence.py

@@ -0,0 +1,71 @@
+#!/usr/bin/env python3
+"""Are a music bank's two waves the SAME instruments filtered, or DIFFERENT parts?
+
+`structures/bgm-two-stems.md` leaves two readings alive for wave 1 -- the rear
+pair of a 4-channel mix, or a second intensity layer -- and notes that runtime
+simultaneity cannot separate them, since both predict it.
+
+This tries a static discriminator.  Magnitude-squared coherence is ~1 wherever
+one signal is a LINEAR FILTER of the other, and ~0 for independent signals, so
+a rear pair modelled as "front pair, filtered" should read high and a different
+arrangement layer should read low.
+
+⚠️ READ THE CONTROLS BEFORE THE MEASUREMENT.  The L-vs-R control below is the
+one that matters and it is the one that limits this tool: see the docs page.
+
+    bgm_stem_coherence.py <w0.wav> <w1.wav> <control.wav>
+
+Waves come from slb_extract_wave.py + ffmpeg; see the docs page for the exact
+offsets and packet counts.
+"""
+import sys, wave, numpy as np
+
+NFFT, HOP, FS = 8192, 4096, 48000
+BANDS = [(0,200),(200,1000),(1000,4000),(4000,12000),(12000,16000),(16000,24000)]
+
+def load(p, nmax, stereo=False):
+    w = wave.open(p); n = min(nmax, w.getnframes())
+    a = np.frombuffer(w.readframes(n), dtype="<i2").astype(np.float64)
+    a = a.reshape(-1, w.getnchannels())
+    return (a[:,0], a[:,1]) if stereo else a.mean(axis=1)
+
+def _acc(x, y):
+    win = np.hanning(NFFT); Sxx = Syy = Sxy = 0.0; k = 0
+    for i in range(0, min(len(x), len(y)) - NFFT, HOP):
+        X = np.fft.rfft(x[i:i+NFFT]*win); Y = np.fft.rfft(y[i:i+NFFT]*win)
+        Sxx = Sxx + abs(X)**2; Syy = Syy + abs(Y)**2; Sxy = Sxy + X*np.conj(Y); k += 1
+    return np.abs(Sxy)**2/(Sxx*Syy+1e-30), Sxx, Syy, k
+
+def coh(x, y): return _acc(x, y)[0]
+def spec(x):   return _acc(x, x)[1]
+
+def row(name, C, f):
+    print(f"  {name:34} " + "  ".join(
+        f"{lo/1000:g}-{hi/1000:g}k {C[(f>=lo)&(f<hi)].mean():.3f}" for lo,hi in BANDS))
+
+if __name__ == "__main__":
+    p0, p1, pc = sys.argv[1], sys.argv[2], sys.argv[3]
+    D = 60*FS; f = np.fft.rfftfreq(NFFT, 1/FS)
+    w0 = load(p0, D); w1 = load(p1, D); ctl = load(pc, D)
+    L0,R0 = load(p0, D, True); L1,R1 = load(p1, D, True)
+
+    # POSITIVE control: an actual linear filter of w0 (one-pole LP + 12 ms delay)
+    a = 0.06; lp = np.empty_like(w0); acc = 0.0
+    for i, v in enumerate(w0):
+        acc += a*(v-acc); lp[i] = acc
+    d = int(0.012*FS); pos = np.concatenate([np.zeros(d), lp[:-d]])
+    sh = np.concatenate([np.zeros(FS), w0[:-FS]])
+
+    print("CONTROLS")
+    row("POS w0 vs linear-filter(w0)", coh(w0,pos), f)
+    row("NEG w0 vs a different bank",  coh(w0,ctl), f)
+    row("NEG w0 vs w0 shifted 1 s",    coh(w0,sh),  f)
+    row("REF w0 L vs R (one perf.)",   coh(L0,R0),  f)
+    row("REF w1 L vs R (one perf.)",   coh(L1,R1),  f)
+    print("\nMEASUREMENT")
+    row("w0 vs w1",                    coh(w0,w1),  f)
+    print("\nENERGY SHARE")
+    for nm,(L,R) in (("w0",(L0,R0)),("w1",(L1,R1))):
+        S = spec(L)+spec(R); t = S.sum()
+        print(f"  {nm:34} " + "  ".join(
+            f"{lo/1000:g}-{hi/1000:g}k {100*S[(f>=lo)&(f<hi)].sum()/t:5.1f}%" for lo,hi in BANDS))