KSPROPSETID_Hrtf3d
The KSPROPSETID_Hrtf3d property set is used to configure the 3D head-relative transfer function (HRTF) for a DirectSound buffer. This set contains optional properties of a 3D node (KSNODETYPE_3D_EFFECTS) on a DirectSound pin instance.
Not all 3D nodes support HRTF processing. A client can send a basic-support query for an HRTF property to a 3D node to determine whether that node is capable of performing HRTF processing. A 3D node that supports the KSPROPSETID_Hrtf3d property set must support all three of the properties in the set.
The definition of this property set assumes that the HRTF algorithm is implemented with infinite impulse response (IIR) filters that represent the effects of an audio source at a single position.
Digital filters typically have an initial transient response. When moving a source from one position to the next, the filter coefficients change and the HRTF algorithm cross-fades the outputs from the filter at the old position to the filter at the new position. The FilterTransientMuteLength member of the KSDS3D_HRTF_INIT_MSG structure specifies the number of samples by which to delay the cross fade in order to avoid rendering the new filter's initial transient. During this time, the output comes from the old filters only. The FilterOverlapBufferLength member (same structure) specifies the total number of samples over which to mute and cross-fade the filter outputs.
When the source moves from the right half-plane to the left, the filters switch. This switch might cause an audible pop. The SwapChannels member of the KSDS3D_HRTF_PARAMS_MSG structure tells the HRTF algorithm to swap the outputs to reverse the location of the source to the other half-plane. The CrossFadeOutput member (same structure) tells the algorithm to cross-fade the output channels after a transition across azimuth angle zero. The OutputOverlapBufferLength member of KSDS3D_HRTF_INIT_MSG specifies the number of samples over which to cross-fade when this transition occurs.
Because of symmetry, only half of the filter coefficients need to be downloaded to the HRTF algorithm when the azimuth angle is zero. The ZeroAzimuth member of KSDS3D_HRTF_PARAMS_MSG indicates when this condition occurs.
For information about configuring HTRF processing through the DirectSound API, see the Microsoft Windows SDK documentation.
The KSPROPSETID_Hrtf3d property set contains the following three members: