linux + piano keyboard support

src/synth/Instruments/PianoString.hpp

@@ -50,7 +50,7 @@ private:
     float mu_ = crossSectionalArea_ * rho_; // linear mass density
     float waveVelocity_ = std::sqrt(stringTension_ / mu_); // transverse wave velocity
     float L_ = 1.0f; // length of string at a given frequency
-    float gain_ = 0.3f;
+    float gain_ = 0.5f;
 
     // f0_ = waveVelocity_ / (2.0f * stringLength_); // fundamental frequency of a non-stiff string
     // f1_ = f0_ * std::sqrt(1.0f + stiffness_); // fundamental frequency of the stiff string