The Haas Effect

The Haas effect, aka the precedence effect, is a binaural psychoacoustical effect. It explains how, when a sound follows another sound separated by a short time delay, listeners perceive it as a single auditory event. This phenomenon dates back to 1949. The first description of this effect appeared in The Precedence Effect in Sound Localization by Wallach, Newman, and Rosenzweig.

The Physics of the Haas Effect

The Haas effect involves an integration interval. Experts refer to it as a time period over which the fusion of two sounds takes place. This interval is usually 5ms for clicks and up to 40ms (for more complex sustained sounds). The localization of the first arriving sound determines the one of the fused sound. This principle is based on the time difference between two sounds with the same intensity.

You can control the Haas effect if the fused sound is 15dB or louder than the first sound. The location of the first-arriving sound dominates the perceived spatial location of the precedence effect. The lagging sound affects the perceived location, but the first-arriving sound suppresses its effect.

Where to Use It

You can apply the Haas effect to modern technology to get a wide, open, and spacious sound that translates into a more realistic sense of depth. Common uses include areas such as music production, sound multichannel encoding, ambience extraction, and reinforcement systems. The Haas effect, directly applied to music production, requires a stereo-delay plugin.  

Users must remember the following tips. Firstly, to set a delay time on a specific side where there is no delay. Secondly, to set a delay time on the opposite side on a range between 1ms and 35ms. Thirdly, to watch for possible loudness increases. The transformation of the mono track into a stereo track, when you insert a stereo delay plugin, may provoke it.