Haas effect is a bin-aural psycho acoustic effect regarding the sound source localization. It is known as the “precedence effect” or the “law of the first wavefront” and it was defined and described by Helmut Haas in his Ph.D. Thesis in 1949.
In short, our ears determine the position of a sound based on which ear perceives it first and its successive reflections (arriving within 1-35 ms from the initial sound) which, will give us the perception of depth and spaciousness. Pretty simple!
In general, we use our pan knobs to position sounds within the stereo field. Briefly put… If we have a sound coming out of a stereo pair of speakers at an equal volume, our ears will interpret that the sound is coming out from the middle. So, panning is not much more than the amount of volume you send to each speaker… Let’s remember that our ears depend on not only volume, but also on time and frequency differences for the localization of sounds.
THE HAAS EFFECT – HOW TO
The concept of the Haas effect can be applied in order to get a wide, open and spacious sound resulting in a more realistic sense of depth. In our example, we’ll use a stereo-delay plug-in to achieve this effect. There are 3 things to remember:
- Set the delay time on the side where you want to perceive the sound is coming from to ‘0’ (no delay)
- Set the delay time on the opposite side anywhere from 1 ms – 35 ms. Solo your track and increase the delay time starting from ‘0’ and listen!
- Watch for a possible loudness increase since you are converting your mono track into a stereo track when you insert the stereo delay plug-in. One suggestion would be to set the ‘MIX’ control on both sides of the stereo-delay to 50%. Adjust your track volume accordingly.
Where you set your delay time yields different results, so it’s best try things out until you find something that sounds good to your ears. Remember though, that the goal here is to make our identical mono tracks sound wider than they really are.
A delay of somewhere around 5 ms on one track will actually enhance directionality and yield an “out-of-phase” type sound, which isn’t what we’re after. For example, if you’ve delayed the left-panned channel by 5 ms, the sound will appear more intense in the right-panned channel.
Up to a certain point, the more delay you add will further enhance directionality. However, once you’ve surpassed say, 10 ms or so, your two tracks will sound wider rather than more or less intense in one channel.
The trick is to keep the delay time below our ears’ echo threshold–approximately 35-40 ms for most people–so that no distinct repeats are audible. You’ll find that you’ve widened the stereo image and added dimension to an otherwise “flat” mono track, without a reverb or an imaging plugin!
OTHER USES OF PSYCHOACOUSTICS IN MIXING
Using the same technique above, you can also reduce directional masking in your mix. When panning doesn’t cut it, we have to rely on the timing component of our hearing to cleverly maneuver throughout the stereo field. You can try using a stereo delay with one channel set to 0 ms while tweaking the other side to taste.
Using the Haas effect’s principles, we can also “thicken” mix elements using the early reflections from a reverb plugin. Because early reflections typically occur well under the 35-40 ms echo threshold of our ears, they’re also within the range of the Haas effect.
Without using the reverb tail and only using early reflections, you can thicken up the initial transients of a sound for a beefier, in-your-face attack.