Precedence effect

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The precedence effect , also known as the law of the first wave front , is a psychoacoustic effect. It says the following: If the same sound signal arrives at a listener with a time delay from different directions, the listener only perceives the direction of the sound signal arriving first; the delayed sound signals are localized in the direction of the first (the first wave front ) .

The law of the first wave front was first described by Lothar Cremer in 1948 . In the English-language literature, the term “precedence effect” is not only understood to mean the law of the first wavefront, but is also summarized with the sum localization .

Scope

  • The precedence effect is effective when the time delay from the first to the following wave front is between 2 ms and a signal-dependent upper limit. This is around 50 ms for speech and up to several 100 ms for music.
  • If the time delay is less than 2 ms, cumulative localization occurs , i.e. H. the perceived direction of the sound signal is between the directions of the sound sources .
  • If the time delay exceeds values ​​of 50 ms (for speech) or 100 ms (for music), the delayed sound may be perceived as an echo ; then it is correctly assigned to its direction of incidence . The time delay after which a delayed sound is perceived as an echo depends on the type of signal. For impulsive signals this can be the case from 50 ms, for signals with an almost constant amplitude the echo threshold can be in the range of 1 to 2 seconds.

A special form of the precedence effect is the Haas effect . Haas showed that the law of the first wave front works even if the level of the delayed sound is up to 10  dB above that of the first wave front. In this case, however, the range of validity is much more restricted and only includes time delays of 10 to about 30 ms.

use

The precedence effect is relevant when listening in closed rooms . With the help of this effect, it is still possible for people to determine the direction of a sound source (e.g. a speaker) even when there are many wall reflections .

For audio reinforcement in large rooms, the Haas effect is used to raise the sound level at distant seats. For this purpose, loudspeakers in the auditorium are controlled in such a way that the loudspeaker signal arrives at the listener about 20 ms later than the direct sound . The listener only perceives the direction of the direct sound, but benefits from the higher sound level generated by the loudspeakers.

See also

Web links