Haas effect: what it is and how it affects the perception of sounds.

A curious psychological effect used by the music and audiovisual industry.

The Haas effect, widely used in the recording industry, is a psychoacoustic effectis a psychoacoustic effect which occurs when two sounds are perceived as if they were only one, even though they were not emitted at exactly the same time.

Although it has been named after Helmut Haas, he was not the only one who investigated this particular sound effect. Let's see more in depth what it is, who investigated it and some examples of applications in the daily life of this effect.

What is the Haas effect?

The Haas effect, also known as the precedence effect or priority effect, is an effect that occurs when two sounds are heard but are emitted almost at the same time.. The second sound is emitted within a very short time, less than 50 milliseconds after the first sound was emitted.

Because the emission of the second sound is so fast, the human ear does not perceive it as an echo, the human ear does not perceive it as if it were an echo, but as if the two sounds were one and the same, even though they were emittedThe second sound is so fast that the human ear does not perceive it as an echo, but as if the two sounds were one, even though they were emitted at different times.

This effect becomes important when determining the location of objects by the sound they emit. Since the two sounds are perceived as if they were one because they have a minimum temporal separation, the spatial location is determined by the first sound, spatial location is determined by the first sound that reaches the ear, which dominates over the second sound.which dominates over the second. Sounds that come after the first will cause the brain to interpret that there is some depth, relating them to the first rather than interpreting them as independent sounds.

Historical background

Actually, and although this binaural psychoacoustic effect has been named after Dr. Helmut Haas, who discovered it in 1949, the truth is that before him there were researches and findings about this same effect.

In fact, in 1948, Lothar Cremer in 1948, Lothar Cremer discovered this effect, referring to it as the "law of the first frontal wave".. A year later, Wallach and co-workers spoke more extensively about the precedence effect, showing how if two sounds were presented almost at the same time they would be heard as if they were one. They were able to observe that after 40 milliseconds of difference in the emission of the two sounds, the echo effect began to occur.

Subsequently, Wallach's group discovered that when two sounds coming from different locations are perceived as one or merged, the brain interpreted that the object was located in a particular place from the first sound heard.not the second. Based on this, they saw that this explained why sometimes, when sound bounces off a wall or furniture in a room, the human ear can interpret that the object emitting the sound is in a different place than it really is.

However, and despite the great discoveries made by Cremer and Wallach, the reason why this effect is known as the Haas effect is due to a publication by Helmut Haas in 1951. In this publication, Haas studied how speech perception is affected by the presence of a rapid repetition of a sound. Haas found that humans localize based on the direction of the first sound heard, regardless of whether or not there is repetition of the sound.

Conditions of onset when perceiving sounds

The Haas effect occurs if the second sound comes after 2 to 50 milliseconds.. It should be noted, however, that the precedence effect varies according to the type of sound. For example, in the case of speech, this effect disappears after more than 50 milliseconds, but for music, the Haas effect disappears after more than 100 ms.

In the various experiments that have been done to investigate this effect, it has been found that the location depends on several aspects:

1. Summative localization

In case the second sound occurs after less than 2 msthe listener will perceive only one sound.

2. Localization dominance

If the second sound is presented after 2 to 5 msIf the second sound is presented after 2 to 5 ms, the listener will also hear a single sound, and the person will interpret the proximity of the object based on the first sound.

3. Delay affects discrimination

The shorter the time between the first and second sounds, The shorter the time between the first and second sounds, the less able one is to be aware that two sounds are being heard..

Applications

The Haas effect is important for hearing in closed rooms, making it possible to determine with this effect the location of an object emitting the sound, although it must be said that the presence of walls can confuse the person since they reflect the sound. the presence of walls can confuse the person because they reflect the sound..

Below we will see some situations in which this effect is used in a premeditated way.

1. Sound reinforcement systems

This type of system is used in public events. By placing several loudspeakers, there is a risk of echoes occurring..

If the Haas effect is taken into account and the loudspeakers are set up in such a way as to ensure that they retransmit with delays of less than 50 ms, it will ensure that two or more sounds are not perceived.

2. Dolby surround

This effect has been taken into account in the development of dolby surround devices. Whether they are televisions or music players, the following are taken into account the importance of both or more loudspeakers outputting the sound at the same time or with very little delay from each other.

Ambient sound

The Haas effect can be used to increase the feeling of being immersed in a particular environment, be it natural, urban or any other type.be it natural, urban or any other type of environment.

One of the best known cases is that of the barber's audio, a reproduction that if listened to gives the sensation of being in a barber's shop and the barber cuts our hair.

In this particular case, the effect of precedence is played with a lot, in addition to making the sound louder in one earphone than in the other, giving the sensation of depth and making us think that we have a pair of scissors nearby.

4. DJs

Many DJs use this effect to give depth to their mixes, as well as to play with echoes and echoes.They also play with the echoes and the volume of their own compositions.

Thus, they can make the melody they are playing feel closer or farther away, as well as play with the perceived position of the loudspeakers.

Bibliographical references:

• Cremer, L. (1948): "Die wissenschaftlichen Grundlagen der Raumakustik", Bd. 1. Hirzel-Verlag Stuttgart.
• Haas, H. (1951). "Uber den Einfluss eines Einfachechos auf die Horsamkeit von Sprache," Acustica, 1, 49-58.
• Litovsky, R.Y.; Colburn, H.S.; Yost, W.A.; Guzman, S.J. (1999). The precedence effect. The Journal of the Acoustical Society of America. 106 (4 Pt 1): 1633-16.
• Wallach, H., Newman, E. B., & Rosenzweig, M. R. (1949). "The precedence effect in sound localization," The American Journal of Psychology, 62, 315-336.