Haas effect

The Haas Effect refers to the brain’s ability to integrate incident sound and early reflections into a single sound. Those early arrivals which occur within the first 5-35ms that are not more than about 10dB louder than the direct sound will be combined and added to the first arrival and localized to its source. If the delayed sound is more than 10dB louder or the delay is greater than 35ms, the listener will perceive distinct echoes.A psychoacoustic phenomenon where an instrument or sounds apparent localization will shift in the direction of the earliest signal. This is a type of sensory inhibition which causes the response to the direct sound source to inhibit response to the reflections. Haas further noted the Precedence Effect: the position of a perceived sonic image created by two sound sources depends on both the arrival times and the relative levels. If two sound sources arrive at the same time and at the same level, human aural perception will image the sound toward the centerpoint between the two sounds. If two sounds are equally loud, the image will shift toward the earliest-arriving signal. Further, if one source is louder, the image can be moved back to the center between the two sources by adding delay, provided that the delay time is less than 25ms. Beyond 25-30ms, the ear begins to hear the delayed sound as a discrete echo and the image shift effect no longer works. This phenomenon is usually used to simulate a stereo image in a monophonic recording where the original signal is panned hard left and a copy is delayed (1-50ms delay) and panned hard right. The Precedence Haas Eeffect may be mitigated by slightly attenuating the volume of the dry sound.

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