Precedence effect

The precedence effect, also called the law of the first wavefront, is a psycho -acoustic effect. He states the following: Does the same sound signal delayed from different directions for a listener to take this true only the direction of the first- arriving sound signal. Delaying the incoming sound signals are localized in the direction of the first signal ( the first wave front ).

Scope

• The precedence effect operates when the time delay between the first wave front and the following wave fronts in the range between 2 ms and about 50 ms. These limits are signal-dependent, while the upper limit language is about 50 ms, it can also be several 100 ms for music.
• If the time delay less than 2 ms, summing localization occurs. The perceived direction of the sound signal is located between the directions of the sound sources. Is applied to summing localization in the intensity stereophony: 2 speakers emit the same signal with different levels. The perceived direction then depends on the level of relationship between the two speakers and is located between the two speaker locations.
• Exceeds the time delay values ​​of 50 ms (for language) or ms, then optionally performed 100 ( with music) of the late arriving sound as an echo; then it is directionally associated with its incident direction correctly.

The time delay from a delay of incoming sound is perceived as an echo is dependent on the type of signal. For pulse signals containing this may be the case of 50 ms. For signals of nearly constant amplitude of the echo threshold may be in the range of 1 to 2 seconds.

A special form of the precedence effect is called the Haas effect. Haas showed that the law of the first wave front itself acts when the level of the incoming sound is delayed by up to 10 dB of the first wave front on the. In this case, the scope is much more limited and however, only comprises the time delay of 10 to about 30 ms.

Use

Relevant is the precedence effect when listening in enclosed spaces. With the help of this effect even in the presence of many wall reflections it is possible for man, nor the direction of a sound source to be determined (eg, a speaker ).

For audio sound in large rooms of the Haas effect is used to raise the sound level at distant seats. To this end, speakers are driven in the audience that the speaker signal arrives at the listener about 20 ms later than the direct sound. The listener perceives this only the direction of the direct sound, but benefited from the higher noise level, the presented by the speakers.

History

The law of the first wavefront was first described in 1948 by Lothar Cremer. In the English literature, the term " precedence effect " not only the law of the first wavefront understood, but it is aggregated with the total localization.