Audio changed speed?

You have had a change in the sampling rate on playback. Sonar sets the sampling rate for the project as a whole and does not change it once it is set. Your audio interface sampling rate has changed somehow so that it no longer matches the project rate. The interface sampling rate can sometimes be changed by other audio applications running in Windows. 

dlion16
perhaps you inserted a tempo change by accident? check the tempo map.
 
otherwise, close and reopen sonar and see if you still have the issue.

A Sonar tempo change does not affect the pitch, which the OP is saying is "about a half step lower."

It has been years since I have stopped using my audio interface for both Sonar and as the Windows Default Audio Device, so I may well be completely off base.
 
I am wondering if you have things set to where Windows and Sonar ARE both using the audio interface, I wonder if you have Windows changing the sample rate to 44.1 k (which is its default), and perhaps have Sonar set to use 48 k.
 
If the above, or some variation, is NOT how you are running, my son had a weird similar thing happening, and it had something to do with audio looping or something like that.  There was some kind of way he had flags/markers on some imported audio loop and just for that one project, it was making the tempo slow down and the pitch lower.  I wish I could remember more about the exact cause, because changing some aspect of that imported audio loop DID fix the issue.
 
If nobody jumps in with a better handle on what I am getting at with the above, then I will circle back in an hour or so and try digging up the thread for you.
 
Sorry my brain is apparently leaking these days - the meds do NOT help with that. :)
 
Bob Bone