Haas effect, also called the precedence effect, is a psychoacoustic effect, described in 1949 by Helmut Haas in his Ph.D. thesis that describes the phenomena of identifying the sound source heard in both ears arriving at different times.The Haas Effect tells us that humans localize a sound source based upon the first arriving sound, if the subsequent arrivals are within 25-35 milliseconds and holds true even if the second sound is louder than the first.
Sound arriving at both ears simultaneously is heard as coming from straight ahead, or behind, or within the head. The Haas Effect describes how full stereophonic reproduction from only two audio channels is possible.
Application in EDMEditIn EDM sounds are often panned to the left and the right but end up as lifeless mono sounding patches without a stereo effect. Although panning does help create a stereo effect, it often sounds dull and lifeless. This is due to the fact that the brain also uses the difference between the time of the arrival of the sounds to generate a clearer stereo image.
Producers can take advantage of the Haas Effect by cloning the channel and panning them to the extreme left and extreme right and applying delays on the channels(with the difference within 25-35 ms). The greater the difference in the delay, the more panned towards the channel with the lower delay it sounds. The effect can be enhanced by passing the channel with the greater delay through a low pass filter to remove the higher frequencies or by changing the amplitude of the sounds, localizing the sound even more.
Note: The difference should be kept within 10 dB otherwise the auditory illusion that only one sound is being generated will be shattered.