The Haas Effect or Precedence effect is how we localize sound. Basically when a sound source hits our ears, it will reach the ear closest to the source, and then reach the other ear. We can use this knowledge to construct an effect rack that does the same thing.
This is much different from panning because it doesn't so much as change the volume on either side, but rather delays the signal instead, and can be a very useful tool in your mixing toolbox.
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The "Haas Side" controls which side is delayed. Generally extreme values are preferred (0, 127) but feel free to experiment. The "Haas Delay" controls the delay time between each side. Finally the "Mask Cut" will gently reduce the volume of the delayed side for a more pronounced effect.
The bottom three knobs will further darken the sound by performing 2 separate cuts on the high frequency content. The first two control a 6kHz cut which is an emulation of the listeners head being in the way of the sound, while the last one is a LPF removing all high frequency content.