PLParEQ is a 10-band Phase-Linear Parametric Equalizer of the highest quality. Each filter may assume any of many different filter characteristics, and operate in either traditional phase-warping mode, or our phase-linear mode. It uses the same internal DSP core as all of our other high-end products. Audio streams are treated in either stereo or mono. Individual filters can be applied to either or both stereo channels, middle only, or side only.
Phase Linear Operation is achieved by processing your sound in both the forward-time and reverse-time directions through classic filters - all in realtime. This completely removes the phase warping caused by IIR filtering, and applies their roll-off twice. So each filter type becomes two: one for classic IIR filtering, and the other for Phase-Linear operation.

More info:
http://www.refinedaudiometrics.com/products-plpareq.shtml