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June 2, 2021

The Haas Effect and How it Works

Although commonly referred to as the precedence effect, the Haas effect is a psychoacoustical effect that was described by Helmut Haas in 1949. This effect states that when two identical sounds are separated by a short number of milliseconds (approximately 40ms or less), our central nervous system processes them as a single sound. Our brain processes these sounds as a single, fused sound when the delay time is below the human echo threshold. This effect also states that when successive sounds coming from sources at different locations are heard as a single sound, spatial location is determined by the first sound to reach the ear, regardless of where the second sound came from.

To simplify this explanation, we determine the source of a sound depending on which copy of the sound arrives at our ears first.

Under what circumstances might we incorporate the Haas effect in our productions?

The most common application of the Haas effect consists of utilizing its psychoacoustical effect to supplement a sounds dimension. For instance, picture a scenario where you’re contracted out as a mix engineer for a song that was recorded by another engineer across the country. In the event that the recording engineer didn’t record vocal overdubs during a chorus section, you can still create the effect of additional vocal stacks by applying the Haas effect to increase the width of the vocal. Conversely, this same principle can be applied to guitars, drums, or any other element of a mix that lacks the desired directionality you’re attempting to achieve.

The Haas Effects, explained visually. One of the signals has a slight delay.

How to apply the Haas effect:

  • Begin by duplicating a mono audio file and panning one channel hard left and the other hard right.
  • Next, apply a short delay to one of the audio tracks. For the most control, make sure that you use either a hardware delay unit or delay plug-in that allows for control over the delay time in milliseconds.
  • Understand that where you set your delay time will dictate if you apply width or if you’re simply creating a short, slap-echo effect. In order to add dimension to the audio track, you will want to make sure that your delay time is below the human echo threshold. If your delay time is calculated above that delay time, you will only be applying an audible echo effect. Remember, the approximate human echo threshold is less than 40 milliseconds.
  • Be mindful of your phase coherence when utilizing the Haas effect. Extremely short delay times can be counterintuitive if applied improperly. For example, if you delayed the right channel by 3 milliseconds, the left channel’s level may sound intensified as a result of phase incoherence. As you increase the delay time, you will notice that rather than an apparent level change, the two tracks will sound wider.

If you’re interested in learning about more audio techniques, consider F.I.R.S.T. Institute’s Recording Arts & Show Production program, which teaches students audio fundamentals in just 11 months.