Music Unfolding has released hD and xEQ, the latest additions to their new "Twister Series" of AU plug-ins for Mac OS X. hD costs $19.99 and xEQ is free.

hD is a distortion effect with harmonic generators. It can generate two pitch-shifted copies of up to two octaves above the input signal - the volume level of the two voices can be set independently. hD also has a sub-octave generator. hD's design uses its harmonic generators to enhance the distortion. The two harmonic voices are mixed into the signal before the distortion stage. The sub-octave generator algorithm was developed specifically for hD. It is latency-free. hD can also be used to generate 12-string guitar effects and as a note doubler.

xEQ is a parametric EQ/Tone Control. It consists of Low and High shelf filters and three Peak/Cut filters. It is useful for placing around distortion effects - place one xEQ before your distortion effect to act as a preamp's tone control; place another xEQ after your distortion effect to simulate a speaker cabinet's frequency response curve. Some example presets are provided; presets that start with "TC" are tone control curves and those beginning with an "SC" are for speaker cabinet response curves.