I'm experiencing some changes in behavior with Sonar that I think happened after an update - but quite possibly could have been caused by another program or global setting...
 
When everything was working well - I could have a project open and switch between Sonar and other programs (i.e. itunes, chrome to play a youtube video, etc.) without issue.
 
Recently - I was working on a project while watching a tutorial on youtube and, one day, I opened up youtube and the video would not play.  When I shut Sonar down and refreshed the browser - everything worked fine.  As it turns out - I can't play any audio while Sonar is open.  
 
I've tried to do some problem solving and found the "Share driver with other..."  setting in the preferences menu.  That's half resolved the issue, although now I hear pops and clicks when I switch to a different program and sometimes the sound gets "stuck" and drones and I have to close out all the programs to get it to stop...  Even if it doesn't get stuck, I find that when I go into another program then come back to Sonar - the speed has slowed down...  (perhaps something with sample rates?)
 
Can anyone help me with this?

If you only have a single audio interface in your machine, you should make sure that Windows is set to playback audio at the same sample rates as you are using in Sonar. This way, the interface won't have to change sample rates when switching windows away from Sonar. The second thing you'll need to do is ensure that Sonar is set to share the interface with other applications in Preferences.
 
If you have two interfaces, you can have Windows use one and Sonar use the other.
 
Regards,
Dan

Great!  I'll have to look into some options.  I have two interfaces, however I'm not using one of them because I've upgraded and haven't been able to sell the old one.  I also could use the built in audio in my computer - are there advantages/disadvantages to hooking up two interfaces?  
 
How do I tell windows to use - say, the built in audio - and Sonar to use something different?

I run with Sonar using the ASIO drivers of my audio interface, and to completely eliminate any conflicts with other programs and Windows, I have the Windows Default Audio Device set to use the internal sound of my computer.  Well, actually, it is connected to an HDMI output to one of my two HDTV's I use as computer display monitors, since they have built-in speakers and HDMI transmits both audio/video together.
 
I don't know if you can have two sets of ASIO drivers running at the same time or not, but for whatever the worth, using the above setup, I have great sound for everything running through the HDMI connection, and that leaves Sonar completely free to be the sole application to access the audio interface's ASIO drivers.
 
I regularly play songs through YouTube or Windows Media Player, and there are never any conflicts.
 
I could also have fed the output from my computer's internal sound chip back into two of my inputs of the audio interface, if I didn't have the speakers in the HDTV I use (or a set of computer speakers), and that would have worked fine, as well.
 
If interested in trying out something like the above, go to Control Panel and click on Hardware and Sound, and you will see a link labelled Manage Audio Devices, and you can choose your Windows Default Audio Device there. It is super easy and super simple, and eliminates contention for the audio interface.
 
Bob Bone
 

As part of my ongoing issues with the latest version of Platinum they had me switch to WDS/KP and I started having the same issue. I have to unplug the USB cable to my Octa-Capture and everything returns to normal when I plug it back in. 
 
Sonar also exits with a problem message when I close it everytime now.
 
Good news is that I've had no crashes in the middle of projects.
 
Hope this helps.

robert_e_bone
I run with Sonar using the ASIO drivers of my audio interface, and to completely eliminate any conflicts with other programs and Windows, I have the Windows Default Audio Device set to use the internal sound of my computer. 

I could do this, however it wouldn't be ideal.  1 - I would like to be able to use my monitor speakers. and 2. I often use headphones through my interface because I have young children and work on projects at night.  I would have to have two sets of headphones and switch between the two...  Unless there is a way to route everything differently...
 
I think this is probably what I need to do:
 

dcumpian
If you only have a single audio interface in your machine, you should make sure that Windows is set to playback audio at the same sample rates as you are using in Sonar. 

 

MGC59
As part of my ongoing issues with the latest version of Platinum they had me switch to WDS/KP and I started having the same issue. I have to unplug the USB cable to my Octa-Capture and everything returns to normal when I plug it back in. 
 
Sonar also exits with a problem message when I close it everytime now.
 

I haven't had any of these problems, but I did find that the latest update doesn't seem to flow as well...  The biggest problem that I've had is that when I open projects through the new start-up menu, it sometimes crashes - however if I open from file menu in the upper left - it works fine...  I like the old start-up menu better...  :(
 
I've also noticed that it's slower to load Soft Synths.  I use Omnisphere a lot and when I click to bring it up - it takes a long time and even goes to "(Not Responding)" but that usually resolves itself within 30 seconds.  Just kind of annoying...
 

I am having the same issue. I will go check the sample rates. It started happening when I upgraded to Windows 10 so still not sure if it is a SONAR problem or Windows 10. What operating system are you using?

I have used my SoundBlaster as Windows audio device with its output connected to my M-Audio input. That was working great except the solution was noisy.
 
I have then switched to M-Audio only, setting its "Software return" as Windows audio device. That is working fine in case the number of bits is the same (16), once I switch to 24 Sonar is working fine but Windows produce no sounds at all.
 
I think the best solution is to use different hardware sound interface for windows and route it to your music interface digitally (spdif). Note that can decrease latency tolerance of your music interface (making clicks) since conventional drivers do not care and they can block the system (Creig has written some time ago that simply enabled but not used HDMI audio driver was problematic for him).

Preferences > Audio > Playback and recording > Share drivers with other programs?
 
Is this checked or clear?
 
JMFT

FWIW, I had a Tascam US 4x4 and I would have to uninstall and reinstall the driver to be able to switch programs. I am back to Focusrite and no issues.