ABSTRACT
In audio in the past, the terms Haas effect and law of the fi rst wavefront were used to identify this effect, but current scientifi c work has settled on the other original term, precedence effect. Whatever it is called, it describes the well-known phenomenon wherein the fi rst arrived sound, normally the direct sound from a source, dominates our impression of where sound is coming from. Within a time interval often called the “fusion zone,” we are not aware of refl ected sounds that arrive from other directions as separate spatial events. All of the sound appears to come from the direction of the fi rst arrival. Sounds that arrive later than the fusion interval may be perceived as spatially separated auditory images, coexisting with the direct sound, but the direct sound is still perceptually dominant. At very long delays, the secondary images are perceived as echoes, separated in time as well as direction. The literature is not consistent in language, with the word echo often being used to describe a delayed sound that is not perceived as being separate in either direction or time.
