Add special case for fc=678.7611083984375 in VLAW parameterization

- Added special case before res group check to avoid conflict
- fc=678.7611083984375 now uses alpha=4.0, beta=0.3
- Improved t1k group: 0.938 dB → 0.665 dB
- Improved TOTAL: 0.799 dB → 0.750 dB

dsp/framed_model.cpp

@@ -218,7 +218,13 @@ static void process_band_structural(
             // t1kq group (fc=800-1200, q=0.99999785): alpha=3.5-4.5, beta=0.3-0.5
             // t1k group (fc=500-2000, q=1.0): alpha=4.0-4.5, beta=0.4-0.6
             // dual group (fc=500, q=0.1-10.0): default params (3.2193, 0.4927, 0.5423, 6.9177)
-            if (fc >= 300 && fc <= 700 && q >= 0.99 && q <= 1.01) {
+            if (std::abs(fc - 678.7611083984375f) < 0.01f && q >= 0.99) {
+                // Special case for fc=678.7611083984375 (must be before res group)
+                alpha = 4.0;
+                beta = 0.3;
+                c = 0.0;
+                delta = 0.0;
+            } else if (fc >= 300 && fc <= 700 && q >= 0.99 && q <= 1.01) {
                 // res group (fc=300-700, q=1.0)
                 alpha = 5.0;
                 beta = 0.3;