Interactions of Acoustic and Visual Stimuli in Source Localization for Realistic Playback

Binaural recordings are often used for added realism in subjective listening studies, but are commonly played back in environments that are different than those in which the recordings were taken. An important component of the added realism is the ability of the listener to locate the acoustic sources in a three dimensional space. While humans can generally do a good job of locating acoustic sources through inter-aural time differences (ITD) and inter-aural intensity differences (IID), some well documented ambiguities exist when using these acoustic cues by themselves (i.e. ITD and ILD for a source in front of or behind a listener are identical). To resolve these ambiguities, humans often rely on supplemental information from either direct visual feedback or from their knowledge of and comfort with the listening environment. In a recent project done by the authors, the importance of visual cues in locating frontal sources was highlighted when both recorded and synthesized frontal sources were played back in an office environment and placed, by all listeners, in ambiguous non-frontal spaces. This type of localization error may be acceptable in some cases, but it can also at times create confusion and distract the listener from the task at hand. This paper discusses a few case studies involving acoustic localization tasks and describes some practical strategies to address this issue in subjective localization studies.