22g: NO-LUT test isolates gap to detector front-end; unified sidechain-clamp hypothesis (knee at 0dBFS, identical renders above)

dsp/framed_model.cpp

@@ -98,16 +98,23 @@ static void process_band_structural(
     constexpr double DRP = 0.2159;
     double rp = RP0 * std::pow(static_cast<double>(band.q), DRP);
 
+    // RT_LUT_OFF=1: EXPERIMENTAL (NOTES 22f) — skip LUT transform entirely,
+    // hypothesis: audio path has NO LUT (FUN_180563a60 was GUI-only, 22b);
+    // mask = blend*exp2(-lvl_raw) directly.
+    static const int lut_off = getenv("RT_LUT_OFF") ? atoi(getenv("RT_LUT_OFF")) : 0;
+
     for (size_t k = 0; k < nbin; k++) {
         double res_k = std::max(static_cast<double>(res[k]), 1e-12);
         double lvl = static_cast<double>(am[k]) / res_k * scale_factor;
-        // dB-domain LUT (FUN_180563a60) on LEVEL before IIR/exp2: keeps both
-        // quiet (t1kq) and loud (t1k) inputs inside the LUT domain [A,B],
-        // avoiding the t<0 clamp collapse that mask-domain LUT hits on loud input.
-        double dB = std::log10(std::max(lvl, 1e-12)) * 20.0;
-        double t = (dB - LUT_A) / (LUT_B - LUT_A);
-        t = std::min(std::max(t, 0.0), 1.0);
-        lvl = std::pow(t, static_cast<double>(LUT_GAMMA)) * LUT_MULT;
+        if (!lut_off) {
+            // dB-domain LUT (FUN_180563a60) on LEVEL before IIR/exp2: keeps both
+            // quiet (t1kq) and loud (t1k) inputs inside the LUT domain [A,B],
+            // avoiding the t<0 clamp collapse that mask-domain LUT hits on loud input.
+            double dB = std::log10(std::max(lvl, 1e-12)) * 20.0;
+            double t = (dB - LUT_A) / (LUT_B - LUT_A);
+            t = std::min(std::max(t, 0.0), 1.0);
+            lvl = std::pow(t, static_cast<double>(LUT_GAMMA)) * LUT_MULT;
+        }
         band_level[k] = static_cast<float>(lvl);
     }