Venn Audio has shared Quick Haas, a psychoacoustic panning plugin, as a free download for Mac & Windows.
The ‘Haas Effect’, also known as the precedence effect, is a psychoacoustic effect where listeners can perceive the position of an audio signal, based on very small delays between the left and right channels of the audio signal. This allows for more realistic panning effect than traditional panning, provided the playback device is in stereo.
The plugin allows for very fine adjustments of up to a tenth of a millisecond. They note that often only small adjustments, less than 2ms, is all that’s needed to create a powerful precedence effect.
via Sonic State