Voxengo describes TEQ-421 as freeware equalizer plug-in for professional music production applications. Here's their full description of it...
This equalizer features only three bands (Triple EQ), finely tuned to deliver good results in many cases, thus being extremely easy to use. Beside this, the plug-in features internal non-parametric harmonic coloration modules (derived from HarmoniEQ plug-in) that produce a smooth saturation and a "presence" effect.
The frequencies of the bands were carefully selected and are not adjustable. These frequencies target specific frequencies that affect sound's perception the most. The best use-case for this plug-in is equalization of unprocessed acoustical recordings that usually lack in modern balance of low, mid, and high frequencies.
The plug-in is equally useful on individual tracks, groups, and master bus. It was designed by tuning to a set of various sound sources, including vocals, acoustic guitars, drums, basses, and full mixes.
Pricing and Availability:
With Jim Heywood
Matths gives it a workout
From recent Brighton gig
With Kavus Torabi and Michael J. York