From b410c944451fe4e796a728997ab33a52f425bae2 Mon Sep 17 00:00:00 2001 From: sylph-decoder Date: Mon, 31 Aug 2026 00:09:43 +0000 Subject: [PATCH] re: run the identity control on the coherence estimator -- it is exact, and the refutation strengthens 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) Claude-Session: https://claude.ai/code/session_01Wuu56cE8vJGTBtn1ppsk8v --- docs/re/structures/bgm-two-stems.md | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/docs/re/structures/bgm-two-stems.md b/docs/re/structures/bgm-two-stems.md index ceb207dd..031384a1 100644 --- a/docs/re/structures/bgm-two-stems.md +++ b/docs/re/structures/bgm-two-stems.md @@ -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 % |