A system comprising a device (204, 206, 400), the device comprising: a processor; memory configured to store a subset of a plurality of head-related transfer functions (HRTFs) for emulating stereo sound from a source in three-dimensional space, each of the HRTFs corresponding to a direction and a distance, as perceived by a user, of the stereo sound; an output interface for receiving audio information from the processor and outputting signals corresponding to the audio information and; the processor configured to: 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 includes the first HRTF; select first two HRTFs, in the subset of the plurality of HRTFs, corresponding to one distance; use the first two HRTFs in the subset of the plurality of HRTFs to obtain a first estimated HRTF when the subset of the plurality of HRTFs does not include the first HRTF; select second two HRTFs, in the subset of the plurality of HRTFs, corresponding to another distance; use the second two HRTFs in the subset of the plurality of HRTFs to obtain a second estimated HRTF when the subset of the plurality of 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 the audio information, wherein the first distance is between the one distance and the other distance. a processor; memory configured to store a subset of a plurality of head-related transfer functions (HRTFs) for emulating stereo sound from a source in three-dimensional space, each of the HRTFs corresponding to a direction and a distance, as perceived by a user, of the stereo sound; an output interface for receiving audio information from the processor and outputting signals corresponding to the audio information and; the processor configured to: 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 includes the first HRTF; select first two HRTFs, in the subset of the plurality of HRTFs, corresponding to one distance; use the first two HRTFs in the subset of the plurality of HRTFs to obtain a first estimated HRTF when the subset of the plurality of HRTFs does not include the first HRTF; select second two HRTFs, in the subset of the plurality of HRTFs, corresponding to another distance; use the second two HRTFs in the subset of the plurality of HRTFs to obtain a second estimated HRTF when the subset of the plurality of 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 the audio information, 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 includes the first HRTF; select first two HRTFs, in the subset of the plurality of HRTFs, corresponding to one distance; use the first two HRTFs in the subset of the plurality of HRTFs to obtain a first estimated HRTF when the subset of the plurality of HRTFs does not include the first HRTF; select second two HRTFs, in the subset of the plurality of HRTFs, corresponding to another distance; use the second two HRTFs in the subset of the plurality of HRTFs to obtain a second estimated HRTF when the subset of the plurality of 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 the audio information, wherein the first distance is between the one distance and the other distance.