The Haas effect is a binaural psychoacoustic phenomenon that was first discovered by Helmut Haas in 1951.
As Haas was experimenting, he looked very closely at how the perception of speech and sound are bound together. He did two experiments in anechoic conditions and in the room with a reverberation time of 1.6 ms to come to this thought. The speech that was prerecorded was produced by two speakers, the left one was 45° to the left, and the right one 3 m far from the listener. As a result, Haas understood exactly how humans are able to localize sound.
After that discovery, the effect, which is psychoacoustical in its nature and relies on how we, as human beings, perceive sounds, was named the Haas effect.
Human hearing system
Human hearing is a system that can perceive mechanical waves, we all know them as vibrations and comprehend them as sensory information. The inner ear collects all upcoming vibrations and transfers them to the brain. The outer ear has two ears in itself and has the ability to distinguish the source and position of the signal. Depending on where exactly the sound source is located, the left or right ear can be quicker than the other in registering the upcoming vibration. If the sound is behind you or in front of you, it is a good chance that you will register it simultaneously.
But despite the fact that human hearing is a very precise and robust thing, it could be easily tricked sometimes. This is where the Haas effect comes into play. If we position two identical sounds with a very marginal time difference, our brains will identify those sounds as one singular sound source. Interestingly enough, we will determine the position of the sound in space only by the first sound. And if the second delayed sound doesn’t exceed the echo threshold, we will perceive those sounds as one vast and airy sound.
Generally, humans do not consider delays in sound less than 40-50 ms to be an echo. So if your delay does not exceed those numbers, which are mostly coherent for the majority of musical applications, and the sound obviously is omnidirectional, you will easily achieve the Haas effect. And the sound should be omnidirectional in the stereo field, which means that the original sound should be mono.
How to use the Haas effect
There are several ways of how to apply the Haas effect in music production, and all of them are dependent on what tools you have at your disposal. The simplest way of achieving this psychoacoustic phenomenon would be simply to put a stereo delay plugin on your mono track. Of course, this digital plugin should have separate precise controls for the delay of each channel. If your delay controls are interpreted as note durations, unfortunately, the Haas effect could not be achieved with this kind of plugin since even 1/128 will be too long of a delay. You are going to need a delay plugin with turning knobs that control delay in milliseconds.
It is pretty straightforward from here. Leave the delay of one channel at 0 ms and put the other one at 40-50 ms. Then adjust it to your personal taste. Since most of the DAWs nowadays come pretty stacked with onboard gear, to come across the delay plugin with those specific controls shouldn’t be hard. But in case you did not find such a delay, there is another way of how to achieve the Haas effect.
Copy and paste your source mono signal on a separate track and just move the copied track slightly to the right. Depending on what DAW you prefer, you might have to turn off the snap-to-grid option first. Some DAWs have that option as a default, and all your tracks would be moved only within conventional notes durations. Since, as it was mentioned before, even the delay of 1/128 would be too long. So with the snap-to-grid option turned off, you are going to have to move your copied track with almost inhuman precision on a length lesser than any traditional note duration.
In case you do not enjoy such gruesome mental exercises, there is one more way of how to apply the Haas effect. It also involves copying and pasting mono source track, but this time no manual labor should be involved.
There are some specific plugins that serve the purpose of delaying separate tracks exclusively. Also, the best part is that there are quite a few time delay plugins of high quality that are absolutely free of charge. Once you get your hands on one of those delays, it is as simple as just turning one knob. So instead of moving tracks manually, just put your delay somewhere between 10 and 50 ms and enjoy your Haas effect.
Also, you might play around a bit with some reverbs adjusting their pre-delay settings. This particular trick might be considered on a fringe science side of things, but such innocent experiments have not hurt anybody yet. Route your mono signal through two separate mono reverb channels and adjust one of them to have reflections lesser than 50 ms, it is not quite the Haas effect at its purest form, but nevertheless, it is an interesting thing to try.
When to use the Haas effect
Whenever you feel like a track recorded in mono does not sit well in the mix, and you feel that you need to add some space and wideness to it, and you do not want to drown it in excessive reverb, you might consider applying the Haas effect.
Traditionally parts that are intended to be wide are recorded using the double-tracking technique. This technique involves recording a part in mono and panning it hard left or right. After that, the part is recorded again and panned in the opposite direction of the stereo field. Some dynamic inconsistencies and slight timing mistakes will give you the effect of stereo presence and wideness.
But there are situations when for one reason or another, double-tracking is not quite possible. For example, lead guitar parts are notoriously hard to double-track due to their usual timing complexity. Here, applying the Haas effect could be quite beneficial if, of course, you do not want to apply wide reverbs and conventional stereo delays.
The other example would be the situation when you do not have any control over the initial recording. Let’s say you are a mixing engineer, and you were presented with the recording session where, for some reason, the acoustic guitar strum part was not double-tracked. This situation provides a perfect opportunity of applying the Haas effect.
More often than not, you might find yourself in the situation when some mono track is in direct conflict with the lead vocals or something just stick out of the mix, and even additional gain-staging does not help. Here, by using the Haas effect, you can widen up those tracks, thus burying them deeper in the mix.
By the way, the rumor has it that there are some new VST plugins that are designed specifically to perform the Haas effect, which is great news since it will save you a lot of time and make your workflow even faster if you are into those kinds of things.
Not to put too fine a point on it, the Haas effect is indeed a very fascinating effect that would greatly influence your mix by adding air and space in it. There are a lot of ways of applying the effect and based on how much free time you have and your eagerness to roll up the sleeves and indulge in some hard work, you can choose that one that will suit you the best. The double-tracking technique is somewhat another way of how your tracks can be wider and spacey, but sometimes applying this particular approach is not possible. For those cases specifically, as with rock music and conflicts within the parts of the mix, for instance, the Haas effect is a genuine tool that will do all the hard work for you. As the music sphere is rapidly developing and the possibility of applying the Haas effect through VST is possible, you can keep up the pace and work faster, which is important these days.