Upper Filter for Audio messages

Hello everyone,

Does anyone know of a tutorial / information on interpreting the Irp for an (class) upper filter Audio driver ?

Right now I am going through the process of commenting the MSVAD sample virtual audio driver and commenting when it does things like changing of format but I was wondering if these details has already been documented for others that have done a upper filter for audio in the past?

Any tips / information on the subject is welcomed.