You need to launch Activity Monitor and note the Process ID for FCP.
Then launch Terminal and type “sudo renice -20 ProcessIDHere”.
In the above example you’d put the Process ID for FCP in the obvious spot. The “-20″ is the highest priority you can give a program. The lowest would be “20″.
After you type that line above into Terminal it’ll ask you for your adminstrative password.
It’ll then show something like:
“ProcessIDHere: old priority 0, new priority -20″
All apps in OS X are a Priority 0, but using the renice command can tell OS X which apps you want to give more juice to.
Thanks to: http://forums.creativecow.net/archivepost/8/494109
