diff --git a/dsp/framed_model.cpp b/dsp/framed_model.cpp
index 0a95d97..af2f24c 100644
--- a/dsp/framed_model.cpp
+++ b/dsp/framed_model.cpp
@@ -84,7 +84,7 @@ static void process_band_structural(
     constexpr float LUT_A = -13.78f;
     constexpr float LUT_B = 68.29f;
     constexpr float LUT_GAMMA = 0.344f;
-    constexpr float LUT_MULT = 4.4f;
+    constexpr float LUT_MULT = 4.2f;
 
     // res^rp term (bridge parity): smooth frequency-dependent floor
     constexpr double RP0 = 0.0275;
@@ -130,10 +130,23 @@ static void process_band_structural(
         mask_out[k] *= kBand768[idx] * kWarp[idx] * std::pow(res_k, rp);
     }
 
-    // Step 9 (NOTES_LEVEL:830): IIR3 inline TWICE (kIIR_A3/B3), post-warp
-    // spectral smoothing of the mask; upper half re-mirrored afterwards.
-    fn529fe0::iir1(mask_out, kIIR_A3, kIIR_B3, nbin, 0.0);
-    fn529fe0::iir1(mask_out, kIIR_A3, kIIR_B3, nbin, 0.0);
+    // Step 9 (NOTES_LEVEL:830 + consumers_out.txt:955-1075): IIR3 inline,
+    // TWO bidirectional passes [reset, forward, backward] x2 (state persists
+    // from forward into backward within a pair; reset between pairs).
+    // y = B3[i]*x[i] + A3[i]*state (decomp operand order verified).
+    for (int pass = 0; pass < 2; pass++) {
+        double st = 0.0;
+        for (size_t i = 0; i < nbin; i++) {
+            double y = static_cast<double>(mask_out[i]) * kIIR_B3[i] + st * kIIR_A3[i];
+            st = y;
+            mask_out[i] = static_cast<float>(y);
+        }
+        for (size_t i = nbin - 2; i >= 1; i--) {
+            double y = static_cast<double>(mask_out[i]) * kIIR_B3[i] + st * kIIR_A3[i];
+            st = y;
+            mask_out[i] = static_cast<float>(y);
+        }
+    }
     for (size_t k = 0; k < half; k++) {
         mask_out[nfft - 1 - k] = mask_out[k];
     }