Where does precedence effect collide?

When a sound and one or more delayed copies arrive within a few milliseconds of each other, the auditory system fuses them into a single event and takes its apparent direction almost entirely from the first-arriving wavefront, discounting the directional information in the later copies. Wallach, Newman, and Rosenzweig's 1949 The precedence effect in sound localization gave the phenomenon its experimental name and showed the lagging sound's direction is largely suppressed up to an echo threshold. Litovsky and colleagues' 1999 review The precedence effect consolidated decades of work under this label. The referent is a localization-dominance mechanism, measured by how little a delayed copy is weighted in the perceived direction.[1][2]

Unit

The echo delay, in milliseconds, over which the first wavefront dominates perceived direction

Recovery means

Not applicable

Measured by

Assessed with lead-lag click experiments and echo-threshold measurements of perceived location and fusion

Sound engineers know the identical mechanism as the Haas effect: if a delayed copy of a signal arrives within roughly 1 to 35 milliseconds of the direct sound, listeners still hear a single source at the earlier loudspeaker even when the delayed copy is somewhat louder. This is exploited in sound reinforcement, where a delayed fill loudspeaker is tuned so the audience still localizes the stage rather than the nearby speaker. Blauert's Spatial hearing treats this engineering use alongside the psychophysics, making clear it is the same construct under a different name. It is tracked by the delay-and-level trade-off at which the image stays anchored to the first arrival.[3][2]

Unit

The delay-and-level trade-off at which the image stays with the earlier source

Recovery means

Not applicable

Measured by

Set in practice by adjusting delay time and relative level until the perceived source stays at the lead loudspeaker

In room and concert-hall acoustics the same construct is called the law of the first wavefront: a listener in a reverberant space localizes a source by the direct sound that reaches the ears first, while the dense field of later reflections, though it adds loudness and spaciousness, contributes little to perceived direction. Blauert's Spatial hearing sets out this principle as the basis for how rooms preserve source direction despite strong reflections. It is the same first-arrival dominance as the precedence and Haas phenomena, here framed for the acoustics of enclosed spaces and assessed through the balance of direct sound to early reflections.[3]

Unit

The balance of direct sound to early reflections that preserves source direction

Recovery means

Not applicable

Measured by

Evaluated from impulse responses via the direct-to-reverberant ratio and the timing of early reflections