fixes for ASIO sound interface

windows/sound.cpp

@@ -481,6 +481,18 @@ std::string CSound::PrepareDriver()
     iMinNumSndBuf = static_cast<int> (
         ceil ( static_cast<double> ( iASIOBufferSizeMono ) / iBufferSizeMono ) );
 
+// TODO better solution
+// For some ASIO buffer sizes, the above calculation seems not to work although
+// it should be correct. Maybe there is a misunderstanding or a bug in the
+// sound interface implementation. As a workaround, we implement a table here, to
+// get working parameters for the most common ASIO buffer settings
+// Interesting observation: only 256 samples seems to be wrong, all other tested
+// buffer sizes like 192, 512, 384, etc. are correct...
+if ( iASIOBufferSizeMono == 256 )
+{
+    iMinNumSndBuf = 4;
+}
+
     Q_ASSERT ( iMinNumSndBuf < MAX_SND_BUF_IN );
     Q_ASSERT ( iMinNumSndBuf < MAX_SND_BUF_OUT );
 
@@ -498,7 +510,7 @@ std::string CSound::PrepareDriver()
             QString().number ( iASIOBufferSizeMono ) +
             QString ( " samples which is too large. Please try to modify "
             "the ASIO buffer size value in your ASIO driver settings (most ASIO "
-            "drivers like ASIO4All or kx allow to change the ASIO buffer size). "
+            "drivers like ASIO4All or kx driver allow to change the ASIO buffer size). "
             "Recommended settings are 96 or 128 samples." ), "Ok", 0 );
     }