Precedence Effect - Appearance

Appearance

The precedence effect appears, if the subsequent wave fronts arrive between 2 ms and about 50 ms later than the first wave front. This range is signal dependent. For speech the precedence effect disappears for delays above 50 ms, but for music the precedence effect can also appear for delays of some 100 ms.

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:

• Summing localization: for time delays below 2 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 stereophony, where two loudspeakers emit the same signal with different 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 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 ms (for speech) or some 100 ms (for music) the delayed sound is perceived as an echo of the first arriving sound. Both sound directions are localized correctly. The time delay for perceiving echoes depends on the signal characteristics. For signals with impulse characteristics echoes are perceived for delays above 50 ms. For signals with a nearly constant amplitude the echo threshold can be enhanced up to time differences of 1 to 2 seconds.

A special appearance of the precedence effect is the so called Haas effect. Haas showed that the precedence effect appears even if the level of the delayed sound is up to 10 dB higher than the level of the first wave front. In this case the range of delays, where the precedence effect works, is reduced to delays between 10 and 30 ms.