1. A method for generating, using a computational signal processing model, coefficients of a head-related impulse response (HRIR) filter usable in rendering audio for playback comprising: receiving parameters describing the location of a sound source, wherein the parameters are defined relative to the position of a head of a listener; determining a first set of filter coefficients from a spherical head component of the signal processing model in response to at least one of the parameters; determining a second set of filter coefficients from a pinna component of the signal processing model in response to at least one of the parameters, wherein the pinna component of the signal processing model includes a front/back asymmetry model to account for a pinna shadowing effect; determining a third set of filter coefficients from a torso component of the signal processing model in response to at least one of the parameters; determining a fourth set of coefficients from a near-field component of the signal processing model in response to at least one of the parameters; and combining the first, second, third, and fourth sets of coefficients by convolution to generate the coefficients of the HRIR filter, wherein the front/back asymmetry model comprises: for each ear, a front/back difference for front elevations in front of the head and a front/back difference for back elevations behind the head determined from a difference between responses for respective elevations that are mirror images of each other, mirrored at a frontal plane, wherein a tilt factor specifies how much of the difference between responses for respective elevations that are mirror images of each other is applied to the front/back difference for the front elevations to boost the front elevations and how much of the difference between responses for respective elevations that are mirror images of each other is applied to the front/back difference for the back elevations as a level cut to the back elevations, wherein the difference between responses for respective elevations that are mirror images of each other is a function of azimuth and elevation; and front/back difference filters for the front and back elevations computed from the front/back differences for the front and back elevations, respectively.