I've been observing small problems with sound smoothness lately, but I finally found a repeatable scenario, albeit an unusual one.
When I set a high CPU demanding app (in this case - prime95 @ 3 or 4 threads) and affinity to 3 cores, and then start other another somewhat demanding app (in this case - running ashampoo burning studio 12) I'm getting sound issues. However, this only occurs when I'm listening to an external, analog FM tuner, which is only connected by line-in. Sound issues are only few squeaks and pauses in moments when I'm running ashampoo and gone away, when the app is finished starting.
It's not happening, when the cpu affinity is set to other 3 cores - except core2 unset (counting from 0-4). Moreover, it's not happening when I'm playing music from Windows Media Player... :)
I've tried to change priority of svchost.exe instantiation depending on the Windows Audio service and Audio Endpoint Builder (even to realtime) with no effect. Maybe I should give more priority to some input-output service that usb is depending?
Audio: Sound Blaster X-Fi Surround 5.1 Pro (USB!) connected by 3x minijack to 5.1 speakers running direct input ; motherboard integrated audio is disabled in BIOS
USB controller: (not sure if only, but as I see on device manager.) Intel 5series/3400 chipset family USB - looks like two - 3b34 and 3b3c
motherboard: Asus P7P55D (bios 2003, newest is only hdd capacity patch )
windows 7 x64 ult (all updates)
Also lately I've different strange issues - when I used my mx5500 keyboard without mice in logitech mode the sound was squeaking all the time - some kind of hi-pitch distortion and also pauses - this problem wasn't solved after disabling usb power saving but after installing logitech app and changed usb-stick mode from base to bluetooth.