Thanks Cian. I just re-read the initial post and realise that your concern was with stuttering graphics, while mine is with stuttering audio, so perhaps I should have started a new discussion on my issue. But since yours is now solved, I hope you don't mind me using this space to discuss my audio stuttering problems. I have already tried increasing the playback and recording caches to 1024mb but am having the same issue. I guess I could try 2048mb but this seems excessive?? Any other ideas on the cause of the problem would be great.

Wow, thank you! I am trying the X2 demo and am relieved to find this was a FEATURE. Ironically, I was using the pause/break key programmed for a mouse click. Can you imagine? ;)

Cian that is correct. It is used to conserve CPU cycles for processing and will slow down the screen updates. This makes Sonar look like its "stuttering".