Optimal source distribution for binaural synthesis over loudspeakers

When binaural sound signals are presented with loudspeakers, the system inversion involved gives rise to a number of problems such as a loss of dynamic range and a lack of robustness to small errors and room reflections. The amplification required by the system inversion results in loss of dynamic range. The control performance of such a system deteriorates severely due to small errors resulting from, e.g., misalignment of the system and individual differences in the head related transfer functions at certain frequencies. The required large sound radiation results in severe reflection which also reduces the control performance. A method of overcoming these fundamental problems is proposed in this paper. A conceptual monopole transducer is introduced whose position varies continuously as frequency varies. This gives a minimum processing requirement of the binaural signals for the control to be achieved and all the above problems either disappear or are minimized. The inverse filters have flat amplitude response and the reproduced sound is not colored even outside the relatively large “sweet area.” A number of practical solutions are suggested for the realization of such optimally distributed transducers. One of them is a discretization that enables the use of conventional transducer units.