Reports have been flooding the web that the
network transfer speed of Windows Vista drops to a low level when the user plays music at the same time. While there does not seem to be a obvious connection between network transfers and sounds being played and everyone would probably consider other possibilities first it seems that a service called MMCSS, the
Multimedia Class Scheduler Service.
Mark Russinovich described the technical process in his blog explaining that ‘when a multimedia application begins playback, the multimedia APIs it uses call the MMCSS service to boost the priority of the playback thread into the realtime range’ which basically means that every other thread - including network transfers - see a performance drop because of this.
The following method has been working for most users who experienced the slowdown in
network traffic in Vista while playing
music.
- Don’t play music while transferring files. This is pretty obvious but probably not the best solution for most users
- Remove the MMCSS dependency of Windows Audio in the registry. To do that navigate to the key HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Audiosrv, right-click the DependOnService string and remove MMCSS from it.
Fix for slow Vista Network Transfer while playing Music 
Linear Mode
