Microsoft system driver. "The Redbook system driver (redbook.sys) is the KS filter that manages the rendering of CD digital audio. The Redbook driver is a client of the SysAudio system driver. The system routes CD digital audio through the file system to the Redbook driver and then to the SysAudio driver. The CD digital audio is rendered on the preferred wave output device (as set in the Multimedia property pages in Control Panel)". More info: http://msdn.microsoft.com/library/defaul...