Ever since I update to Reason 12, I have had this weird issue where the DSP usage would jump to very high values when Reason was not the focus application (active).
And I got the obvious crackles / ugly audio buffer overflow with pops and clicks because of that.
Whenever I selected Reason again (in focus), the dsp dropped to normal values and the crackles / clicks / pops were gone.
The odd thing was that the task manger did not show anything different with or without Reason in focus.
The other software was not very CPU intensive, although the GPU did seem to peek quite high (probably because of the higher resolution of the new Reason 12 interface.
I did some testing and found out that when I set the sample rate of my interface to 44100 hz it got a bit better. But it was not gone and my other Windows applications gave issues (even after restarting), so I put that back to 48Khz.
Changing the multithreading (max nr of audio threads) option to 2 threads worked better (it was gone).
I have 4 cores, so there are still 2 left for other applications.
Now I’m not sure why this would make such a difference, nor am I sure if the GPU is causing this crackling. But for now it is at least a big improvement.