Akai MPK mini

I've recently started using Sonar Platinum and am very pleased with the purchase (made the switch from Ableton). There's one thing I'm having a problem figuring out and that's the input response time of my mpk mini while in Sonar: I press a key on my midi controller and there seems to be about a 1/2 second delay before the note is registered and output. I've performed numerous searches for tips on how to adjust the timing in Sonar but can't find anything, and none of my fiddling with the midi preferences makes any difference in the response time. Can anyone help with this? Is it simply an issue with the mpk mini? Am I overlooking something obvious in the interface?
 
 
Thanks!
 
 
 

If the controller is USB then you have a good input to drive the midi soft synths. 
But it's hard to get the output latency down to a reasonable amount without using ASIO drivers. MME drivers are fine to play music from your computer but are the worst choice for real time monitoring of a DAW. 
The best solution is to purchase a audio interface like a Scarlett 2i2 just to get the asio drivers. 
One other thing that causes midi latency is having certain effect plug ins running like LP 64.