minor improvement

adjusting the nsim stabilization parameters

'''
|Score type |MSE               |Min score         |Max score         |Mean score        |
|-----------|------------------|------------------|------------------|------------------|
|Zimtohrli  |0.073622255247300 |0.611416768760542 |0.797709696340402 |0.734967593303992 |
|ViSQOL     |0.115330916105424 |0.520833375452983 |0.801480831107469 |0.675101633981268 |
|2f         |0.129541391104905 |0.484687555319526 |0.797475783883375 |0.661870345773127 |
|PESQ       |0.147425552045669 |0.342342966279351 |0.841271127756762 |0.647128996775172 |
|CDPAM      |0.153471222942756 |0.441558428344727 |0.728779141125759 |0.620699318941738 |
|PARLAQ     |0.185057687192323 |0.445261140223642 |0.784370761057963 |0.587162756572532 |
|AQUA       |0.223207996944378 |0.331645933512413 |0.739286336419790 |0.547804951221731 |
|PEAQB      |0.225217321572038 |0.278744167467764 |0.851011116004117 |0.553935720513487 |
|DPAM       |0.315810440183130 |0.186717781679534 |0.690564701717118 |0.460415212267967 |
|WARP-Q     |0.339686211572685 |0.067600137543649 |0.777119464646524 |0.475793617709890 |
|GVPMOS     |0.412937133868407 |0.006851162794410 |0.783946603687895 |0.412912222208318 |
'''

cpp/zimt/nsim.cc

@@ -199,9 +199,9 @@ float HwyNSIM(const hwy::AlignedNDArray<float, 2>& a,
         return Mul(delta_a, delta_b);
       });
   const Vec two = Set(d, 2.0);
-  const Vec C1 = Set(d, 64.820932997704162);
-  const Vec C3 = Set(d, 11.285860868315538);
-  const Vec C4 = Set(d, 1e-6 * 2.9262932000000021);
+  const Vec C1 = Set(d, 69.020932997704165);
+  const Vec C3 = Set(d, 76.258402868315542);
+  const Vec C4 = Set(d, 1e-7 * 12.46293200000002);
   float nsim_sum = 0.0;
   const Vec num_channels_vec = Set(d, num_channels);
   const Vec zero = Zero(d);