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re: run the identity control on the coherence estimator -- it is exact, and the refutation strengthens

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sylpheed-port disqualified a difference instrument of their own and named the rule:
before asking whether an instrument can measure a difference, ask whether it
returns zero for no difference. Mine had never had that test -- its positive
control was a filtered copy at 0.94, which I had taken as the ceiling.

Identity reads 1.0000 in every band, and a linear filter with NO delay also reads
1.0000. The 0.94 was entirely the 12 ms delay's windowing cost. So the ceiling for
a filtered copy is 1.0 and the measured 0.027 midrange is further from it than the
original control implied.

It also adds an argument the first pass missed: a delay depresses coherence
uniformly (0.9288..0.9380 flat), while the measurement is 0.027 midrange against
0.83 at HF. The shape is inconsistent with a delayed filtered copy too, which was
the remaining route by which a rear pair could have produced it.

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
2026-08-31 00:09:43 +00:00
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@@ -102,6 +102,28 @@ the other. Controlled first: a real filter of wave 0 reads **0.93–0.94** in ev
band, a different bank reads **0.001**, and wave 0 against itself misaligned by
1 s reads **0.004–0.057**.
✅ **2026-08-31 — the identity control, which I had not run, and it strengthens
this.** `sylpheed-port`'s rule after a disqualified instrument of their own:
*before asking whether an instrument can measure a difference, ask whether it
returns zero for no difference.* Applied here:
| | coherence, all bands |
|---|---|
| **wave 0 against itself** | **1.0000** |
| a linear filter of it, **no delay** | **1.0000 / 0.9999** |
| the same filter **+ 12 ms delay** | 0.9288–0.9380 |
So the estimator is **exact** at identity, and the 0.93–0.94 above is entirely the
**delay's windowing cost**, not the estimator's ceiling. **The true ceiling for a
filtered copy is 1.0**, which puts the measured **0.027** midrange further from it
than the original control implied.
📌 It also adds an argument the first pass did not make: a delay depresses
coherence **uniformly across bands** (0.9288…0.9380 is flat). The measurement is
**not** flat — 0.027 in the midrange against 0.83 at HF. So the observed shape is
inconsistent with a *delayed* filtered copy as well as an undelayed one, which was
the remaining way a rear pair could have produced it.
| band | w0 vs w1 | w0's own L vs R | energy in w0 |
|---|---|---|---|
| 0–200 Hz | 0.169 | 0.321 | 71.4 % |