Well, it is clear to me that this is a lot harder than I previously thought. I still have a "basic" question regarding the stacking of drivers. All the information I have seen on WDM filter drivers, state that filter drivers sit above or below a function driver and "transparently" filter IRPs . I installed a simple "passtrough" driver as an UpperFilter driver to the MSVAD virtual audio device from the DDK and it worked as expected, logging the IRPs with KdPrint. After that I modified the INF file in order to install the passthrough filter driver as a function driver, including registering wave interfaces for this driver. I manually configured the MSVAD virtual audio driver as a LowerFilter of this Passthrough filter driver ( that was actually installed as a function driver ). This worked, but I am not sure if this is somthing that I shouldn´t have done. Generally, If I have a filter driver "XYZ" as an UpperFilter to a function driver "ABC" , can I install "XYZ" as a function driver and have the "ABC" driver as a lowerfilter to XYZ? Would it have the same effect? This same setup did not work when using USBaudio as a LowerFilter to the passthough driver The passthough driver refused to load. Dimitr Prado > >from what I understand a lower filter will not work, how can the lower > filter > >know which "virtual device" the user application used? > > > > Because above you, there will be two driver stacks: two copies of > usbaudio.sys, two copies of sysaudio.sys, two copies of wdmaud.sys, two > devices exposed to user mode. I don't know whether it has to be a lower > filter to usbaudio.sys or an upper filter to usbd.sys, but I believe > that's the spot where you need to branch off your second device. Each > request will come to you from a different FDO. You'll merge them and > forward it on. > > If this is just a hobby task for you, to avoid buying another set of > speakers, you should probably forget it. You're probably talking about > five weeks of development and debugging work. ****************** WDMAUDIODEV addresses: Post message: mailto:wdmaudiodev@xxxxxxxxxxxxx Subscribe: mailto:wdmaudiodev-request@xxxxxxxxxxxxx?subject=subscribe Unsubscribe: mailto:wdmaudiodev-request@xxxxxxxxxxxxx?subject=unsubscribe Moderator: mailto:wdmaudiodev-moderators@xxxxxxxxxxxxx URL to WDMAUDIODEV page: http://www.wdmaudiodev.de/