I have narrow down the reason why an APO built with WDK 8.1 will not load on Win 8.1. It is a dependency issue. When I build with WDK 7.1, there is a dependency on MSVCRT.DLL. When I build with WDK 8.1, the dependency is on MSVCR120.DLL. MSVCR120.DLL is available on Win 7, but not available on Win 8.1, so the APO loads on Win 7, but not on Win 8.1. Since MSVCRT.DLL is available on both Win 7 and Win 8.1, a APO built with WDK 7.1 loads on both. Any help on resolving this dependency issue is appreciated. Leonard From: wdmaudiodev-bounce@xxxxxxxxxxxxx [mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Tim Roberts Sent: Wednesday, May 14, 2014 4:18 PM To: wdmaudiodev@xxxxxxxxxxxxx Subject: [wdmaudiodev] Re: SFX, MFX, EFX Leonard Shoell wrote: In order to make these changes for 8.1, I've updated to build the APOs with Visual Studio 2013 updated with WDK 8.1, instead of building with WDK 7.1. Without any changes to the code, it builds and runs on Win 7. However, on 8.1 Windows will not load the APO. Even after making the changes for SFX/MFX, they still do not load on 8.1, but load on 7. I've experimented with lots of things, but still cannot get 8.1 to load the APOs. But, if I build with WDK 7.1, they load with no issues on 8.1. Any ideas? Is 8.1 looking for something I'm not supporting when I build with WDK 8.1? I was able to turn our LFX APO into an EFX on 8.1; a single binary works for both cases, so it can be done. You have to implement IAudioSystemEffects2 and implement GetEffectsList. Your Initialize routine has to check for APOInitSystemEffects2. Your INF has to add one of the properties PKEY_FX_StreamEffectClsid PKEY_FX_ModeEffectClsid PKEY_FX_EndpointEffectClsid and one of PKEY_SFX_ProcessingModes_Supported_For_Streaming PKEY_MFX_ProcessingModes_Supported_For_Streaming PKEY_EFX_ProcessingModes_Supported_For_Streaming For the most part, I think that was it. -- Tim Roberts, timr@xxxxxxxxx Providenza & Boekelheide, Inc.