Sound plays but video pauses then track goes very fast
Frame skips when screen recording
Low frame rate randomly mid song
If something in the background starts up, or does something, this will use a bit of your CPU. Often having a knock on effect on Audiosurf.
Disabling everything isn't always an option. If you have a MCP (multiple core processor), you can change the cores programs access and execute on.
Download and install Process Explorer (There are other applications but I won't cover them (I don't use them either)). This is a Microsoft endorsed tool, essentially an extension to taskmanager with some extra features. It is safe to use, for those who are doubtful about using 'special' software.http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx
Open Audiosurf and Process Explorer
Find Questviewer.exe in the process list
Right click on Questviwer.exe and select "Set Affinity"
Limit the cores Audiosurf executes on to one. Note, you can set this to any core though I recommend choosing any other than the first, ie core 0.
The majority of single threaded applications and your OS default to core 0, thus setting AS elsewhere means it won't be disturbed (as much) by background and OS usage spikes.
Oddly enough, AS can show increased performance and frames when run in a single core state.
You will have to do this every time you launch Audiosurf. (Mincus has a batch script about that can automate the process)
When using Fraps and other screen recorders, limit those to a separate core to AS to minimise their interference with CPU access.
There's more detail to the how and why I've missed out for the sake of simplicity.