Editing Precedence effect (section)

== Conditions for occurrence ==
The precedence effect occurs if the subsequent wave fronts arrive between 2&nbsp;ms and about 50&nbsp;ms later than the first wave front. This range is signal dependent. For speech, the precedence effect disappears for delays above 50&nbsp;ms, but for music, the precedence effect can still occur with delays approaching 100&nbsp;ms.<ref>
Blauert, J.: Spatial hearing - the psychophysics of human sound localization; MIT Press; Cambridge, Massachusetts (1983), chapter 3.1</ref>

In two-click lead–lag experiments, localization effects include aspects of ''summing localization'', ''localization dominance'', and ''lag discrimination suppression''.  The last two are generally considered to be aspects of the precedence effect:<ref>
{{cite journal
 | journal = The Journal of the Acoustical Society of America
 | title = The precedence effect
 | author = Litovsky, R.Y. | author2= Colburn, H.S. | author3=Yost, W.A. | author4= Guzman, S.J.
 | volume = 106
 | pages = 1633–16
 | year = 1999
 | url = http://murphylibrary.uwlax.edu/digital/journals/JASA/JASA1999/pdfs/vol_106/iss_4/1633_1.pdf
 | doi=10.1121/1.427914
 | pmid=10530009
 | issue=4 Pt 1
 | bibcode = 1999ASAJ..106.1633L
 }}</ref>
* Summing localization: for time delays below 2&nbsp;ms, listeners only perceive one sound; its direction is between the locations of the lead and lag sounds. An application for summing localization is the [[intensity stereo]]phony, where two loudspeakers emit the same signal with different [[Sound pressure#Sound pressure level|levels]], resulting in the localized sound direction between both loudspeakers. The localized direction depends on the level difference between the loudspeakers.
* Localization dominance: for delays between 2 and 5&nbsp;ms, listeners also perceive one sound; its location is determined by the location of the leading sound.
* Lag discrimination suppression: for short time delays, listeners are less capable of discriminating the location of the lagging sound.

For time delays above 50&nbsp;ms (for speech) or some 100&nbsp;ms (for music) the delayed sound is perceived as an echo of the first-arriving sound, and each sound direction is localized separately and correctly. The time delay for perceiving echoes depends on the signal characteristics. For signals with impulse characteristics, echoes are perceived for delays above 50&nbsp;ms. For signals with a nearly constant amplitude, the threshold before perceiving an echo can be enhanced up to time differences of 1 to 2 seconds.

A special appearance of the precedence effect is the Haas effect. Haas showed that the precedence effect appears even if the level of the delayed sound is up to 10&nbsp;dB higher than the level of the first wave front. In this case, the precedence effect only works for delays between 10 and 30&nbsp;ms.