ProTools 9 CPU Overload

[andrewcleaton]

I'm running PT 9.06 on a 27" iMac 3.4 GHz i7 with 12GB RAM, Lion 10.7.2.

Audio Interface is an RME Fireface UC.

A session I'm working on at the moment regularly locks up during playback with the following warning dialogue:

"A CPU overload error occurred. If this happens often, try increasing the H/W Buffer Size in the Playback Engine Dialogue, or remove some plug-ins."

The thing that really puzzles me is that the System Usage meter only ever shows a maximum of 15% CPU (RTAS). Nothing I do in the Playback Engine Dialogue (even massive buffer settings) makes a difference. It's not a massive session - 12 Audio Tracks with some native ProTools Dynamics, EQ and a couple of reverbs. Virtual instruments (mostly Xpand!) have been rendered as audio and the Instrument & MIDI tracks made Inactive. So I'm narrowing the possibilities down to MOTU Mach5 v2 (installed but not used in this session) and Melodyne Editor (Single Track) v1.

Approx 20% of these lock-ups result in the iMac (Including all other apps e.g. iTunes) losing contact with the RME interface - requiring restart.

All ideas/advice gratefully received.

Thanks!