Problems when using all 4 cores vs. 3 cores

[hopelessennui]

I've searched around and tried to find someone with a similar problem, but couldnt.

Im running:
Mac 2.6 Ghz Quad core, OSX 10.6.8, 8 GBs RAM
Pro Tools HD 9.03 (but it also happened when i was on PT 8)
HD 2 PCIe, 96 I/O

This issue has been going on for a long time (like 3 years!), but hasn't bothered me till now since I have some big sessions that are maxing out my machine.

I've noticed that on these large sessions, running on all 4 cores and 512 buffer, playback will crackle and eventually stutter and get stuck looping 2 seconds or so of audio, maybe 4 times till it drops out and gives me one of a few different CPU overload/buffer size errors. The strange thing is the CPU activity meter was at around 70% or so when it drops out, the CPU ISNT being maxed out.

THEN, when I set it to 3 cores It wont do the stuttering/loop/dropout EVEN THOUGH the CPU activity is peaking out around 90/95% (mind you I still get some pops and crackles since the CPU is being taxed)

Im not sure where the problem lies since this happened in PT 8 and 9, could be an issue with OSX or my computer?

Basically, I wish I could use all 4 of my cores for extra power! I know i could raise the buffer etc etc, but if im recording i cant raise the buffer.

Thanks in advance for any help!

[nst7]

This is not a bug or defect. Protools has always recommended using one less core than your max, which helps, rather than hinders. It allows a little bit of processing for other tasks. When doing this, you can increase the remaining cores up to 99%.

I know it seems counter-intuitive, but your system will actually run smoother this way. You're actually not losing any power. There have been many threads about this.

Also, if you get one of the newer Macs that have hyper-threading, it works the same way. For example, a quad-core Mac Pro or Imac with hyper-threading will show up in Protools as 8 cores (it adds virtual cores). In this case, you set it to 7 (basically allowing half of a core for other stuff).

Some have also found it works even better to have even less cores, such as when using an 8 core, that shows up as 16. It might be good to have only 11 cores allocated. If you get one of these newer Macs in the future, you'll have to experiment to find the sweet spot.