|Microsoft DirectX 9.0|
Secondary buffers played simultaneously are automatically mixed in the
On VXD drivers, the DirectSound mixer produces the best sound quality if all your application's sounds use the same WAV format and the hardware output format is matched to the format of the sounds. If this is done, the mixer does not need to perform any format conversion. Your application can change the hardware output format by creating a primary sound buffer object and calling the IDirectSoundBuffer8::SetFormat method. To do this, you need the Priority Cooperative Level. You must set the format of the primary buffer before creating any secondary buffers. DirectSound will restore the hardware format to the format specified in the last call every time the application gains the input focus.
On WDM drivers, setting the primary buffer format has no effect. The format is determined by the kernel mixer. For more information, see DirectSound Driver Models.