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Record an unresolved discrepancy in the SBlk record size

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Range measured: level 0 SBlk, 24..19508, 19484 bytes.

The 0x7f/0x47f marker words sit at 12-byte spacing on 144 of roughly 180
occurrences, with 24-byte and larger gaps accounting for the rest. So there is
a 12-byte structure.

That contradicts the autocorrelation. If records were 12 bytes, stride 12
should peak, and it does not:

  stride 12   +0.237
  stride 20   +0.175
  stride 24   +0.237
  stride 40   +0.454
  stride 48   +0.239

40 is not a multiple of 12, so the measurements disagree rather than one
explaining the other. Recorded as open rather than resolved in favour of
either: the marker spacing says 12, the period says 40, and 40 being twice as
strong is the more surprising of the two.

Worth resolving before attempting a record layout, because a layout built on
the wrong one will parse plausibly and be wrong.
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2026-10-11 04:06:31 +02:00
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@@ -565,3 +565,34 @@ one. Neither applies here, and the tiling identity cannot be inflated at all.
This is the strongest form of evidence produced in this project: a structural
invariant confirmed by two methods that do not share a failure mode.
## Sound bank SBlk: a 12-byte marker that does not explain the 40-byte period
**Range measured:** level 0 `SBlk`, 24..19508 (19,484 bytes).
**Method:** positions of the `0x7f`/`0x47f` marker words, and their spacing.
**Result:** those markers sit at **12-byte spacing on 144 of roughly 180
occurrences**, with 24-byte and larger gaps accounting for the rest. So there
is a 12-byte structure in the data.
**But that contradicts the autocorrelation.** If records were 12 bytes, stride
12 should be the peak. It is not:
| stride | excess over shuffled |
|---|---|
| 12 | +0.237 |
| 20 | +0.175 |
| 24 | +0.237 |
| **40** | **+0.454** |
| 48 | +0.239 |
40 is not a multiple of 12, so the two measurements disagree rather than one
explaining the other. Recorded as an open discrepancy rather than resolved in
favour of either: the marker spacing says 12, the period says 40, and 40 being
twice as strong is the more surprising of the two.
This is the first place in this project where two sound measurements of the
same data point at incompatible answers. Worth resolving before any record
layout is attempted, because a layout built on the wrong one will parse
plausibly and be wrong.