Binaural Capability of Locating Sound Sources of Information Signals

Abstract

The purpose of the work done was to estimate the human binaural capability of locating stereo sound sources of information signals, especially speech, choir singing, and symphonic music as compared to pulse signals. The measurements were conducted in an average-sized hall where sound was emitted by a stereo system consisting of two loudspeakers with the base width of 4.5 m.Based on the results of analysis of existing methods of binaural sound perception modelling, the estimation was performed based on correlational processing of signals recorded using a head dummy placed in various points of the room.For the recording points selected, the maximum time delays between signals arriving at a listener’s left and right ears were calculated, and the interaural cross-correlation functions were obtained. The general functions, especially the peak shift, correlation interval, and peak sharpness (including the conditions when it splits into two individual ones), were analysed. The correlation factor values and levels were calculated. As a result, the conclusions regarding the capability of locating an imaginary sound source were made based on the cross-correlation function factors values, which simplified the application of this method in practice.Based on the results of experiments conducted and on the subjective sensations of perception, the authors have come to the conclusion that a stereophony area has sizes much wider than those assumed earlier from the signal time delay of 1 ms at a receiving stereo pair (representing a shift of an imaginary source towards the ear perceiving the signal earlier).At the same time, it was found that signals with a speech component are much harder to locate than pulse signals. While music signals, especially symphonic music, are close to pulse signals in terms of human locating capabilities.The found patterns have allowed us to introduce adjustments to the stereophony area calculations. Based on the research results, we suggest defining the stereophony zone border by the correlation factor value of 0.5. Given that, the interaural cross-correlation function properties and subjective perception provide for acceptable speech legibility and music transparency. The key conclusion is that this area is quite narrow for speech signals and is actually limited to the time delay of signals arriving at left and right ears – around 1 ms. Music signals have a wider stereophony area defined by the time delay between perception binaural pair components of around 10 ms. Therefore, sizes of a stereophonic sound area ought to be defined with regard to an information signal’s type.Ref. 14, fig. 3, tabl. 3.