Ever see your CPU meter spike?

Yes, first time for me too, happened yesterday, while I was playing a project with a lot of samples (6x Session Drummer 3 and 1 BFD, and a few others..). But only at the beginning of the playback. Then I've not seen this spike again.

Some synth plugins continue to generate audio even when there is no MIDI input, and some effect plugins generate low-level noise even when there is no audio input. This can be easily observed. Open a blank project and you'll see the CPU meter sitting at zero; drop in an instance of the TTS-1 and you'll suddenly see activity on the CPU meter. 

The point is that even when the project is idle, the audio engine may still be processing output data, filling the output buffer while the driver empties it. If the computer were to then undertake some CPU-intensive background activity, you'd see the CPU usage jump up, possibly even up into the red. 

SONAR's CPU meter indicates how long it's taking to service the audio buffers, so it can rise not just because of demands placed on it by SONAR but by other, non-audio processes that steal time from the business of servicing audio data.

In addition to that, laptops may switch to a slower CPU speed or shut down cores in order to conserve power when they're idle. This will also make the CPU meter rise because the CPU is less efficient when its performance has been degraded in this way.

One or more things may have been happening when you saw that spike. The laptop may have entered a power-saving mode. If you have a wireless network adapter active it may have decided to poll the network for other computers. You may have even been attacked by a port scanner or denial-of-service attack. You could have spyware or a virus. You could have had an anti-virus scan kick in that's scheduled for when the CPU isn't busy. If you use the Comodo firewall, it could have decided to play its tricks and open up 50 network connections to the mothership. Windows Update may have decided to check for updates. The MS Office index service may have started up. The laptop may have initiated hibernation mode. 

IOW, there are a gazillion reasons why your CPU suddenly got busy even when you weren't playing back your SONAR project, as long as SONAR was generating any output at all.

Hi all,you can try to set thread scheduling model at value 2 in AUD.ini,it's very important for cpu cicles behaviour.Best.Roby

It's called ThreadSchedulingModel. At 8.3 a new thread scheduling model was introduced to provide better load balancing. Setting this variable to 0 reverts to the pre-8.3 thread scheduling model, 1 enables the new model. Setting it to 2 is a third option that may help quad-core and higher systems, but is not recommended for dual-core systems.