Apply logarithmic scaling

To match perceived loudness

src/minidexed.cpp

@@ -1786,14 +1786,17 @@ void CMiniDexed::getSysExVoiceDump(uint8_t* dest, uint8_t nTG)
 	dest[162] = 0xF7; // SysEx end
 }
 
-void CMiniDexed::setMasterVolume (float32_t vol)
+void CMiniDexed::setMasterVolume(float32_t vol)
 {
-	if(vol < 0.0)
-		vol = 0.0;
-	else if(vol > 1.0)
-		vol = 1.0;
+    if (vol < 0.0)
+        vol = 0.0;
+    else if (vol > 1.0)
+        vol = 1.0;
 
-	nMasterVolume=vol;
+    // Apply logarithmic scaling to match perceived loudness
+    vol = powf(vol, 2.0f);
+
+    nMasterVolume = vol;
 }
 
 std::string CMiniDexed::GetPerformanceFileName(unsigned nID)