![]() One of the findings of Haas and his peers was that not only can a sound and its copy be perceived as a singular, fused sound, but that this effect persists even if the sound and its reflection come from substantially different directions.įor very short delays of about 2–5 ms the location is judged almost exclusively from the initial sound, and as the delay increases past about 5 ms the perceived level and spaciousness of the sound increases while still retaining the apparent location of the initial sound. ![]() Ok, so what about the direction bit? This is where it gets really interesting, at least from a production and mixing perspective. If we wanted to simulate a Haas delay, we would need a simple delay, perhaps an EQ, and to tune the delay time to somewhere between 1 and 40 ms depending on the sound source. Taken together, this gives us some interesting information. Not too shabby, eh?) This can extend up to 50, or even 100 ms for certain sounds, however it is dependent on a number of factors.įirst, what is the nature of the sound? Is it short and percussive, or sustained and even? Second, who is the individual doing the hearing? Third, what is the nature of the reflection? Is it louder? Softer? Has its EQ been changed substantially? Is it embedded in an underlying reverberant field? So long as the delay is less than about 40 ms, all of these factors work together to determine whether a reflected-or delayed-sound is heard as being part of, or distinct from, the original sound. (Side note: remember Joseph Henry from 1851? He estimated this at 50 ms. Generally speaking, a delay time is considered to be in the Haas zone if it is less than about 30–40 ms. So then, what’s “a sufficiently short time?” As Haas and his peers discovered, this is a bit more complicated. So OK, maybe a delay and a little EQ could replicate what we’re talking about. And while the acoustic properties of the wall might change the tonal balance-or EQ-of the reflected sound a little, it’s not going to radically distort it or add qualities that weren’t there in the first place. Sound goes in, some specified amount of time later the same sound comes out. Now, not a delay with feedback and modulation and other cool, effect elements, just a simple time delay. That’s useful because this is something we could potentially emulate with a simple delay. ![]() It then continues on, hits the wall, bounces back, and a very short time later that reflection-or copy-also enters your ears. As the presenter speaks, their voice first passes you and enters your ears. To visualize this, imagine you’re listening to a presenter giving a speech on a stage out in an open field, except there’s a wall behind you. We’ll get to that, but for now, this gives us some insight that “copies” basically means acoustical reflections off walls and other types of surfaces. All this to say, more than a few people have been interested in this effect over the years. al were nearly 100 years late to the game, for it was in 1851 that Joseph Henry wrote “On the Limit of Perceptibility of A Direct and Reflected Sound.” 1851! Not only that, but his margins of accuracy were surprisingly close to the findings of Wallach, Haas, and their contemporaries nearly a century later. ![]() ![]() Some six months before his thesis was published, Hans Wallach and his colleagues published very similar findings in The American Journal of Psychology under the title, “The Precedence Effect in Sound Localization.” However, Haas was not the first to describe this phenomenon. thesis, and for whatever reason, the audio world seems to have gotten stuck on that. So why the “Haas effect?” Well, in December 1949, one Helmut Haas described this effect in his Ph.D. The Haas effect is also known as the precedence effect. Moreover, even if they come from different directions, the perceived direction of origin will be dictated almost entirely by the sound that arrives first. The Haas effect occurs when a listener experiences two sounds-often copies of one another-that are separated by a sufficiently short time as a single sound event. ![]()
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