Haas Effect: What It Is And How It Affects The Perception Of Sounds
The Haas effect, widely used in the recording industry is a psychoacoustic effect which occurs when two sounds are perceived as if they were only one, despite not having been emitted exactly at the same time.
Although he was named after Helmut Haas, he was not the only one who investigated this particular sound effect. Let’s take a closer look at what it is, who investigated it, and some examples of applications of this effect in daily life.
The Haas effect, also known as the precedence effect or priority effect, is an effect that occurs when two sounds are heard but they are made almost at the same time. The second sound is emitted after a very short time, less than 50 milliseconds after the first sound was emitted.
Since the emission of the second sound is so fast, The human ear does not perceive it as if it were an echo, but as if the two sounds were one despite the fact that they have been issued at different times.
This effect becomes important when determining the location of objects by the sound they emit. When two sounds are perceived as one as they have a minimum temporal separation, spatial location is determined by the first sound that reaches the ear, which dominates over the second. The sounds that come after the first will cause the brain to interpret that there is a certain depth, relating them to the first rather than interpreting them as independent sounds.
Actually, and although this binaural psychoacoustic effect has been named in honor of Dr. Helmut Haas, who discovered it in 1949, the truth is that research and findings on this same effect were made before him.
In fact, In 1948, Lothar Cremer discovered this effect, referring to it as the “law of the first frontal wave.”. A year later, Wallach and collaborators 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 both sounds, the echo effect began to occur.
Later, Wallach’s group discovered that when two sounds come from different locations they are perceived as one or merged, the brain interpreted that the object was located in a specific 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 that emits them is in a different place than it really is.
However, and despite the great discoveries carried out 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 rapid repetition of a sound. Haas discovered that humans localize based on the direction of the first sound heard, regardless of whether or not there is a repetition of it.
The Haas effect occurs if the second sound comes between 2 and 50 milliseconds later. It should be said, however, that the precedence effect varies depending on the type of sound. For example, in the case of speech this effect disappears if more than 50 milliseconds pass, however, for music, the Haas effect disappears after more than 100 ms.
In the various experiments that have been done to delve deeper into this effect, it has been seen that the location depends on several aspects:
1. Summative localization
In case the second sound occurs after less than 2 ms the listener will only perceive one sound.
2. Location dominance
If the second sound appears after between 2 and 5 ms the listener will also hear a single sound, and the person will interpret the closeness of the object based on the first sound.
3. Delay affects discrimination
The less time passes between the first and second sounds, the less ability you will have to be aware that you are hearing two sounds.
Applications
The Haas effect is important for hearing in closed rooms, making it possible to determine with this effect the location of an object that emits the sound, although it must be said that the presence of walls can confuse people since they reflect sound.
Below we will see some situations in which this effect is used deliberately.
1. Sound reinforcement systems
These types of systems are used in public events. When placing multiple speakers, there may be a risk of echoes occurring.
Taking the Haas effect into account and configuring your speakers to ensure that they transmit with delays of less than 50 ms will ensure that two or more sounds are not heard.
2. Dolby surround
This effect has been taken into account when developing devices with Dolby surround. Whether televisions or music players, it is well kept in mind the importance of both or more speakers emitting sound at the same time or with very little delay each other.
3. Ambient sound
The Haas effect can be used to increase the feeling of being immersed in a certain environment whether natural, urban or any type.
One of the best-known cases is that of the barber’s audio, a playback that if listened to gives the sensation of being in a hair salon and the barber cuts our hair.
In this specific case, a lot is played with the precedence effect, in addition to making the sound heard in one headphone louder than in the other, giving the sensation of depth and leading one to think that we have a pair of scissors nearby.
4. DJs
Many DJs use this effect to give depth to their mixes in addition to playing with echoes and the volume of his compositions.
Thus, they can make the melody they are playing feel closer or further away, in addition to playing with the perceived position of the speakers.
