Ty Ford wrote:
The Haas effect has to do with how many milliseconds of delay can be
used before the delayed signal sounds like a discrete echo.
Typically that's around 20 mSec.
** The Hass effect has to do with the perceived direction and level of a sound that is followed by an echo arriving a short time later. An echo arriving from a different direction, even if significantly louder, does not alter the apparent direction of the first arriving sound.
Several times I have been asked to track down mysterious leakage of signal from the PLF of a mixing desk to the FOH outputs. The was none found.
On each occasion, the operator had phones plugged into the desk left sitting in front of him while he PFLd various mic channels. A he did so, the voice or instrument concerned jumped up in level - due to the Hass effect.
Of course, no other person could hear this level change unless they also sat at the desk.
https://en.wikipedia.org/wiki/Precedence_effect#History
..... Phil