When two versions of the same sound presented are separated by a sufficiently short time delay (below the listener's echo threshold), listeners perceive a single auditory event; its perceived spatial location is dominated by the location of the first-arriving sound (the first wave front).
[6] In 1951 Haas examined how the perception of speech is affected in the presence of a single, coherent sound reflection.
Haas found that humans localize sound sources in the direction of the first arriving sound despite the presence of a single reflection from a different direction, and that in such cases only a single auditory event is perceived.
If the reflection's higher frequencies are attenuated, echo suppression continues to occur even if the delay between the sounds is somewhat longer.
[11] The precedence effect can be employed to increase the perception of ambience during the playback of stereo recordings.
This effectively extracts the recording's existing ambience, while leaving its foreground "direct" sounds still appearing to come from the front.
[13][14] The effect was taken into account and exploited in the psychoacoustics of the Fosgate Tate 101A SQ decoder, developed by Jim Fosgate in consultation with Peter Scheiber and Martin Willcocks, to produce much better spatiality and directionality in matrix decoding of 4-2-4 (SQ quadraphonic) audio.
Many older LEDE ("live end, dead end") control room designs featured so-called "Haas kickers" – reflective panels placed at the rear to create specular reflections which were thought to provide a wider stereo listening area or raise intelligibility.
[15] However, what is beneficial for one type of sound is detrimental to others, so Haas kickers, like compression ceilings, are no longer commonly found in control rooms.