The Haas Effect

The History of the Haas Effect

The precedence or Haas effect was first discussed in 1949 in the works of H. Wallach, E. Newman, and M. Rosenzweig in their publication "The Precedence Effect in Sound Localization." The authors discussed the phenomenon in this 1949 paper two years before the publication of the 1951 paper by Haas, "On the Influence of the Single Echo on the Intelligibility of Speech." This was after the precedence effect became known as the "Haas effect." The authors point out that in 1930, von Bekesy reported a precedence effect, "Meaning a suppression or concealment of the sound image which arrives later."

Integration Interval

The authors use earphones and loudspeakers to study a time interval over which the fusion of two sounds occurs. The integration interval is between 5 ms for clicks and up to 40 ms for more complex sustained sounds. The first arriving sound's localization largely determines the fused sound's localization. It is based on the time difference between the ears when the two sounds have nearly the same intensity. The authors point out that the precedence effect can be overridden if the later arriving sound is 15 dB or louder than the first sound.

Psychoacoustical Effect

You can observe the Haas effect as a psychoacoustical effect. When a sound is followed by another sound separated by a sufficiently short delay (below the listener's echo threshold), listeners perceive a single auditory event. Its perceived spatial location is dominated by the location of the first-arriving sound (the first wavefront). The lagging sound also affects the perceived location. However, the first-arriving sound suppresses its effect.

Application

The Haas effect applies to many modern technology areas, including sound reinforcement systems, ambiance extraction, multichannel audio encoding, etc. Here, we will mention the application of the Haas effect in music production. So, you can use it to get a wide, open, and spacious sound that results in a more realistic sense of depth. In our example, we'll use a stereo-delay plug-in to achieve this effect.

Try to Remember

There are three things to remember:

1) Set the delay time on the side where you want to perceive the sound is coming from to '0' (no delay)
2) Set the delay time on the opposite side anywhere from 1 ms to 35 ms. Solo your track, increase the delay time starting from 0, and listen!
3) Watch for a possible loudness increase since you convert your mono track into a stereo track when inserting the stereo delay plug-in. Therefore, I suggest setting the 'MIX' control on both sides of the stereo-delay to 50%. Adjust your track volume accordingly.