re: a music bank is two stems that play together -- not intro+loop, and

not something to concatenate

Q10, and it starts by withdrawing the question's own premise. BGM_001 is
not three sub-waves of 10 KB / 4.47 MB / 4.67 MB: the 10 KB is the bank
header. A bank is exactly TWO waves, and across all 32 BGM banks on the
disc the two always have the SAME duration -- equal to 0.01 s over
lengths from 37 s to 277 s. That alone kills intro+loop and kills two
halves of one piece, both of which require unequal lengths.

Four banks appear to break the rule and do not: BGM_106-109 are the known
leading-region straddle, and the giveaway is that the entry named
BGM_107.slb contains BANK id=1108. The seek packet counts pin each join
exactly, so they realign to the same two-equal-waves shape rather than
being dropped as noise. That trap goes in METHOD.

Then the roles, by decoding both waves to PCM. They are
sample-synchronous: transient-envelope correlation searched over +/-5 s
peaks at lag +0.00 s, and both waves stop at the same millisecond,
167.663 s. Two stems of one performance, meant to sound at once. Wave 1
is quieter, has almost no bass and is far more L/R-decorrelated, which
reads as a surround-rear pair or a second intensity layer -- I cannot
separate those two from the file, and say so: ChannelMask is 0x0002 on
both, and this game's channel metadata is already documented as
meaningless.

Two things the port needs that are NOT on the disc, both marked as
authored: the track is not a seamless loop (BGM_001 fades out and is
followed by 6.15 s of silence, no loop-point field found), and nothing
names which bank the menu plays -- all 32 BGM cues are numeric.

docs/re/REFUTED.md

@@ -119,6 +119,20 @@ neighbourhood, not just the line.
 * "a set-difference over file names can see reuse" → it cannot; **join per
   USER**. Per-pak copies are ×6.
 
+
+## Audio
+
+* "`BGM_001.slb` is three sub-waves (10 KB + 4.47 MB + 4.67 MB)" → the 10 KB is
+  the **bank header**; a bank is **two** waves.
+* "a music bank's two waves might be intro + loop, two variations, or two halves"
+  → they are **two stems of one performance, played together** — equal duration
+  in 32/32 banks, and sample-synchronous.
+  [`structures/bgm-two-stems.md`](structures/bgm-two-stems.md)
+* "`BGM_106`–`BGM_109` break the two-wave rule" → they are the leading-region
+  straddle; realigned across entry boundaries they obey it.
+* "the cue table names which BGM belongs to which screen" → all 32 BGM cues are
+  numeric (`BGM_001`…`BGM_109`).
+
 ## Units, weapons, effects and assets
 
 * "`Generic` (394) is the unit datasheet" → refuted.