Spatial Audio Processing: MPEG Surround and Other Applications

3.6 Source localization in complex listening situations

In addition to the spatial hearing knowledge presented so far, for spatial audio processing and coding it is useful to understand how the auditory system determines the locations of sources in complex listening scenarios. The relation between interaural time difference (ITD) and interaural level difference (ILD) and source direction in free-field is obvious and a conclusion that the auditory system discriminates the source direction as a function of ITD and ILD is in this case rather plausible. However, some phenomena have also been described for which it is not obvious how the auditory system processes ear entrance signal properties for localization of sound sources. For example, when a number of sources are concurrently active, ITD and ILD are likely to be time varying and in many cases their values do not correspond directly to source directions. In an enclosed space, when sound from sources not only reaches the ears of a listener directly, but also indirectly from different directions, the matter of localization of the sources becomes even more complicated. Playback of ‘real-world’ stereo and multi-channel audio signals usually mimics listening to multiple concurrently active sources in rooms. For the task of spatial audio processing or designing a coding scheme for spatial audio it is helpful to understand which signal properties are important to the auditory system for source localization, source width, and envelopment ...