When creating a sound buffer, your application must specify the control options needed for that buffer. This is done with the dwFlags member of the DSBUFFERDESC structure, which can contain one or more DSBCAPS_CTRL* flags. DirectSound uses these options when it allocates hardware resources to sound buffers. For example, a device might support hardware buffers but provide no pan control on those buffers. In this case, DirectSound would use hardware acceleration only if the DSBCAPS_CTRLPAN flag was not specified.
To obtain the best performance on all sound cards, your application should specify only control options it will use.
If your application calls a method that a buffer lacks, that method fails. For example, if you attempt to change the volume by using the IDirectSoundBuffer::SetVolume method, the method succeeds if the DSBCAPS_CTRLVOLUME flag was specified when the buffer was created. Otherwise the method fails and returns the DSERR_CONTROLUNAVAIL error code. Providing controls for the buffers helps to ensure that all applications run correctly on all existing or future sound devices.