Reducing head-related transfer function data volume

A method comprising:

• storing a subset of a plurality of head-related transfer functions (HRTFs) for emulating stereo sound from a source in three-dimensional (3D) space, each of the HRTFs corresponding to a direction from which the stereo sound is perceived to arrive, by a user hearing the stereo sound;
• obtaining a first direction from which first stereo sound is to be perceived to arrive, by the user;
• determining whether the subset of the plurality of HRTFs includes a first HRTF corresponding to the first direction, wherein the plurality of HRTFs include the first HRTF;
• selecting a first and second stored HRTFs in the subset of the HRTFs, wherein directions that are associated with the first and second stored HRTFs are closer to the first direction than directions of other HRTFs in the subset of the HRTFs;
• applying the first stored HRTF to an audio signal to obtain a first intermediate signal;
• applying the second stored HRTF to the audio signal to obtain a second intermediate signal;
• and
• generating output signals for headphones based on the first intermediate signal and the second intermediate signal.

A computer-readable medium comprising computer-readable instruction for configuring one or more processors to:

• store a subset of a plurality of head-related transfer functions (HRTFs) for emulating stereo sound from a source in three-dimensional (3D) space, each of the HRTFs corresponding to a distance and direction from which the stereo sound is perceived to arrive, by a user hearing the stereo sound;
• obtain a first direction and a first distance from which first stereo sound is to be perceived to arrive, by the user;
• determine whether the subset of the plurality of HRTFs includes a first HRTF corresponding to the first direction and the first distance, wherein the plurality of HRTFs include the first HRTF;
• select first two HRTFs, in the subset of the HRTFs, corresponding to one distance;
• use the first two HRTFs in the subset of the HRTFs to obtain a first estimated HRTF when the subset of the HRTFs does not include the first HRTF;
• select second two HRTFs, in the subset of the HRTFs, corresponding to another distance;
• use the second two HRTFs in the subset of the HRTFs to obtain a second estimated HRTF when the subset of the HRTFs does not include the first HRTF;
• determine a third estimated HRTF of the first HRTF based on the first estimated HRTF and the second estimated HRTF;
• and
• apply the third estimated HRTF to an audio signal to generate output signals for driving headphones,
• wherein the first distance is between the one distance and the other distance.