Review of Digital Filter Design and Implementation Methods for 3-D Sound

In this paper, we discuss methods for digital filter design with application to 3-D sound. A review of existing filter design methods for binaural and transaural processing is presented. New methods that take into account the nonuniform frequency resolution of the human ear are explored. Listening tests have been performed to determine the subjective preference of different designs. 0 INTRODUCTION Measurements and models of head-related impulse responses (HRIR) and the corresponding frequency domain transfer functions (head-related transfer function, HRTF) of human subjects or dummy heads are the source of information for the research of spatial hearing and applications of binaural technology (see, e.g., [1] [5] for fundamentals on these subjects). These transfer functions evaluated at discrete azimuth and elevation angles are sufficient for the synthesis of realistic three-dimensional sound events for headphone or loudspeaker listening. One of the problems in 3-D sound synthesis, however, is the computational load of accurate HRTF approximation. To overcome this, both computationally efficient and perceptually relevant digital models of HRTFs have to be created. 3-D sound system design can be divided into two cases according to the reproduction method: 1) binaural processing for headphone listening, and 2) transaural processing for loudspeaker (2 speakers) listening [3]. The significant difference in these methods is the crosstalk that is introduced in loudspeaker listening and that has to be canceled in transaural synthesis. In this work, different methods for digital filter design with application to 3-D sound are discussed. A short overview of HRTF filter design can be