Mixing Music with the Haas Effect
by Alexander Richardson
The “Haas Effect” is an under-appreciated and mostly unknown psycho-acoustical effect, which is one of the 2 major defining factors for localisation within a stereophonic phantom imaging. It is an effect defined by the amount of delay time between the first instance of sound (heard by the ear closest to the sound source) and the second instance or delayed sound (heard by the ear furthest from the sound source). The Haas Effect is largely undiscussed amongst most engineers however for the sought after mixing engineers it is a secret weapon that allows them to enhance their dimensionality.
The Haas Effect
“Haas Effect Also called the precedence effect, describes the human psychoacoustic phenomena of correctly identifying the direction of a sound source heard in both ears but arriving at different times. Due to the head’s geometry (two ears spaced apart, separated by a barrier) the direct sound from any source first enters the ear closest to the source, then the ear farthest away” (Rane Corporation 2011).
What is the Haas Effect? Haas Effect is a delay that occurs 20-35ms after the original sound and is particularly useful as spatial/directional information. Helmut Haas was the first to document the event and its effect in great detail however it would fanciful to pronounce him the author of the Haas Technique.
How does it occur? The human ear has the ability to interpret intricacies of sound way further than what we can describe, for the sake of the post, as ‘first order comprehension’. I will define first order comprehension as easily definable and/or audible sound anomalies. These may include musical anomalies such as rhythm, melody, instrumentation, style, etc or sound information/quality phenomena such as timbre. First order comprehension anomalies are memorable and could be easily identified during or even after listening. Second order comprehension may contain musical anomalies such as inflections, method of playing, accents, etc. or sound information anomalies such as spatial content, stereo imaging, panning, ‘second order’ delays, etc. The Haas effect would be categorised into the third and final order of comprehension because even after its application, the delay (20-35ms) is so quick that the ear cannot discernibly detach the delay from its original sound. The effects can be heard when it is applied as phase, chorus or more importantly (in a correctly laid out stereophonic environment) as location information and it can therefore be described as a ‘third order’ delay.
So, how does this aid the human brain to establish location? In a natural environment, let’s say your bedroom, there are natural reflections everywhere. As the sound source creates its first burst of sound; the sound waves project in all directions with a general focus of where the sound source was facing. The sound waves then splash off the walls as reflections. The human brain has been designed to interpret the reflections as an indication of location (as well as many other things) but specifically with an emphasis on early reflections occurring within 20-35ms of the original burst of sound and typically 10dB softer.
Application of the Haas Effect on a Mix
Having an understanding of the everyday use of The Haas Effect is an important factor here. In a mixing environment we are attempting to create a visual painting with sound across a stereophonic canvas. Consider for a moment that you are blind and walking through a room. It is impossible to discern with any other sense, whether the room is large or small, concrete or brick, full of furniture or empty… Early reflections are your key to that information.
Across a stereophonic field we can create a similar anomaly using a delay. A typical use of the Haas Effect is to pan the original signal all the way to the right and the delayed signal all the way to the left (or vice versa). This is because it gives a widening effect caused by phasing and a distinct lack of sound source information in the centre. The standard application is simple, effective and achieves its widening effect however there are some more advanced uses of the effect.
One way that the brain discerns distance from a sound source is by volume. Therefore the depth of the reflection can be moved by reducing or increasing its volume. In a stereophonic field, location of an image can be moved across the Y-axis by changing the volume ratios between the left and right speaker. Therefore we can define which direction the reflection came from. It can be concluded that a mixing engineer could define the dimensions of a virtual space using early reflections and position it accordingly using the above parameters.
It is important to note that this effect will create a chorusing effect in mono. How close the delay is panned to its original signal defines how much chorusing occurs. It is encouraged to choose your delay time whilst listening in to the comb filtering effects in mono because there will be a desirable delay that sounds better than others when summed in mono. Chorusing is unavoidable if and when the stereo signal is summed to mono. Some engineers suggest that the effect sounds muddy when summed to mono.
Written by Alexander Richardson
Izhaki, R 2012, Mixing Audio, 2nd Edition, Focal Press, Oxford
Owsinski, B 2006, The Mixing Engineer’s Handbook, 2nd Edition, Thomson Course Technology, Boston.