1. A method for generating coefficients of a head-related impulse response (HRIR) filter for use 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 model in response to at least one of the parameters; determining a second set of filter coefficients from a pinna model in response to at least one of the parameters, wherein the pinna model includes a front/back asymmetry model to account for a pinna shadowing effect; determining a third set of filter coefficients from a torso model in response to at least one of the parameters; determining a fourth set of coefficients from a near-field 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.