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The amount of information present in HRTFs and the required processing capabilities for real-time and inter-active binaural rendering have long been a challenge for many applications for binaural rendering. More recently, parametric methods to capture the perceptually-relevant information from HRTFs have been developed. By means of extracting perceptually-relevant attributes from HRTF pairs, binaural rendering can be performed at lower complexity compared to the employment of HRTF convolution. Furthermore, parameter-based binaural rendering can be effiently integrated with parametric audio coders. Last but not least, parametric spatial processing can be used to provide a more convincing spatial reproduction for conventional stereo signals. This paper provides an overview of the perceptual consequences and limitations of HRTF parameterization, its applications, and relevant standardization efforts.

Loudspeakers are often modelled as a rigid piston in an infinite baffle. This model is for real loudspeakers somewhat limited in two ways. One issue is that a loudspeaker is not rigid and a second issue is that a loudspeaker is mostly used in a cabinet. Both issues are addressed here by developing the velocity of the radiator in terms oforthogonal polynomials known from optical diffraction theory as Zernike circle polynomials. Using these polynomials we develop semi-analytic expressions for the sound pressure from the radiator in two different cases: as a flexible flat radiator mounted in an infinite baffle, and as the cap of a rigid sphere. In the latter case the comparison is done not only for the pressure but also for other quantitiesviz. the baffle-step response, sound power and directivity, and theacoustic center of the radiator. These quantities are compared withthose from a real loudspeaker.