The new Communications device role was added in Windows 7 to help communication-centric applications provide a better communication experience for device selection. To support this new role, each endpoint now has a separate timestamp property for each device role, as follows:
To accommodate these changes, the following modified algorithm describes how Windows 7 determines a default audio endpoint for any specific role:
The audio subsystem loops through all the ACTIVE endpoints with a matching device role to find the endpoint with the most recent timestamp property. The timestamp property indicates the last time an endpoint was set as the default audio endpoint.
Otherwise, the audio subsystem resorts to the system default audio endpoint heuristic algorithm to determine the default audio endpoint.
Support for SetupPreferredAudioDevices was removed from Windows 7 because of the following non-deterministic nature:
Although each physical audio device can expose multiple audio features or endpoints (such as a microphone, a speaker, and a headphone), SetupPreferredAudioDevices does not allow control at the audio endpoint level.
The default audio endpoint settings that result from this INF directive are affected by the order in which its driver exposes an audio endpoint. The last exposed endpoint overrides all previous settings.
The Windows 7 Media Class Installer ignores this directive when it installs audio drivers. Therefore, when an audio driver is installed on Windows 7, the endpoints on the device do not necessarily become the default audio endpoint as they did on Windows Vista. You should update your Windows 7 audio driver INF files accordingly.