Perception of sound: Haas effect

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The name Haas effect is given to a physical phenomenon that takes place when the brain perceives sound. Let's consider the case of a sound generated by a single source and let's imagine that we are inside a room and sitting at a certain distance from it. First of all we will be reached by the signal that comes directly from the sound source and afterwards by the signal's reflections bouncing off the walls. This delay is because the reflected sound has a longer way to go to reach the listener compared to the direct signal. If the two signals arrive slightly delayed from one another, both are perceived by the brain as a single sound coming from one single direction. The direction identified by the brain as being that of the sound source is the one belonging to the signal that reaches the ears first (this is true even if the second wave's intensity is greater than the first wave's) and for this reason the effect is also called precedence effect. This effect takes place when the delay between two signals is sufficiently small, to be precise it must be less than 30-35 ms. This time interval is called the Haas zone:

Equation 2.2. The Haas zone 

[0 - 35ms]

When the delay between the signals steps out of the bounds of the Haas zone we perceive two distinct sounds and we enter the domain of the echo effect, where the listener perceives two sounds as being distinct. The Haas effect is utilized in sound reinforcement systems on signals sent to delay towers [Sound reinforcement ] .


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