Hi,
I found something really interesting today, something which was an issue in GarageBand years ago. Like so many others I've had issues with sudden CPU spikes and uneven CPU load in Logic 9 (I'm on a 27 inch Thunderbolt i5 iMac with an Apogee Duet 2 audio interface) and I've been experimenting with disabling inputs, ensuring an audio track is always selected when not recording, trying to optimize things using buses - all the normal stuff. The issues still persisted however and was driving me nuts.
Suddenly I recalled this old Garageband issue where the graphics were using a lot of CPU and the solution was to zoom out until the whole song fit on one screen, i.e. avoid the live scrolling. I tried this in Logic today (by de-selecting the "running man" catch icon in the arrange window) and to my surprise the CPU load was dramatically reduced. Also tried making the window smaller, bascially limiting the area Logic needs to redraw - same effect!
Now this seems like a real bug to me, can't understand why the GUI update thread should ever be able to interfere with the audio, but at least on this iMac if I exapnd the arrange window to fill all 27 inches of screen real estate and rec-enable an audio track I can easily reproduce the problem.
Hope this helps someone.
/alex
