title: midiOutShortMsg and midiOutSetVolume with output in stereo
body: <p>I'm writing C++ code to output midi messages. I need this to work in stereo, so that some notes are played through the left channel/speaker, others through the right. If I call midiOutSetVolume(midiOutHandle, 0xFFFF) followed by several calls to midiOutShortMsg, with each call separated by a few hundred milliseconds, the notes come through the left speaker. Likewise if I first call midiOutSetVolume(midiOutHandle, 0xFFFF0000) before the calls to midiOutShortMsg everything comes out the right speaker. However if I attempt to simultaneously output one note through the left speaker and one through the right by doing the following:</p>
  
  <pre><code>midiOutSetVolume(midiOutHandle, 0xFFFF);
  midiOutShortMsg(...);
  midiOutSetVolume(midiOutHandle, 0xFFFF0000);
  midiOutShortMsg(...);
  </code></pre>
  
  <p>Both notes simply come out the right speaker. I thought if I perhaps had 2 separate handles to the device I could set one to play the left channel notes, the other the right. However if I try and open 2 handles to the same device via 2 calls to midiOutOpen I get an MMSYSERR_ALLOCATED error on the second call.</p>
  
  <p>Any advice much appreciated.</p>