I honestly don't know how diagnostically relevant this will be, but if you're up for it you can try listening to what the speech recognition engine hears:
Create a new command, in the "Add a Command" window click "Other >", "Sounds", "Captured Audio".
Set the "Type" option to "Captured audio (Recognized or Unrecognized)", check the "Play back the captured audio" option, click "OK" to add the action, click "OK" to close the "Add a Command" window, click "Apply" to save the changes to the profile.
Now speak into your microphone so you see the bar move, stop speaking and wait until the bar stops moving, then right-click the command you created and choose "Execute" from the context menu. What you've just said should be played back.
Does it sound normal? Is the volume low?