Why does Pro Tools perform better when it is using fewer cores?

[CME]

Some good info so far. Another thing to consider is you're telling how much CPU power to spend on RTAS ("Real-Time" audio suite) processing. Some plug-ins, especially VI's, use non-realtime code. As does the OS and other background tasks. And running real-time and non-realtime code in the same CPU (core) can cause issues. So you're balancing the available power for realtime and non-realtime code. If you're using a lot of VI's you may set the engine much lower than someone working with strictly audio. It doesn't mean you're not using the other CPUs. Just not for RTAS processing. :)

[Bob Olhsson]

It really means that you should just try a different setting if you run into any problems.

[zion]

I think that this is an area were Pro Tools could use some improvement. Many other audio and video apps out there do a much better job of utilizing more cores. A lot of them can use 100% hyper threading and all with stability. Vegas Pro, Sonar, just to mention a couple and many of these apps incorporate VTi's and all sorts of plugins with all different approaches to coding. So let's not make excuses for Pro Tools, they can do better. I for one am happy with Pro Tools, but I expect more from them. Clearly they are not taking full advantage of the processing power that is available and let me say I've notice this on Mac and Windows Systems so lets not lay blame on the hardware. Even with all things built to Pro Tools Specs and optimizations they still come up short in this category. I also would like to add, I have tested this with hyper threading on and off as well as Intel turbo-boost on and off. Either way it does not take full advantage of the the processing power that is available. Maybe Pro Tools could stand for some better coding or at least raise the standard for third party venders.