Here's what Stone Deaf say about the PDF-2:
PDF-2 Parametric Distortion Filter. This is the younger brother of the original PDF-1 we built and as used by Josh Homme, Nick Valensi and many other infamous guitarists. The PDF-2...What’s there to say other than its the successor to our very popular PDF-1, with reduced noise floor, adjustable gain knob and dual foot-switch for clean and dirty channels what is there not to love. Its one hell of a versatile pedal that's applicable to many instruments. Analogue Piano, Bass, Drums, Synth and Electric and Acoustic guitars this little beast of a circuit has been used on. On top of these impressive features it now boasts expression input control feature for wah wah, phaser and manual tonal shifts as standard. One of the most useful pedal based EQ, Boost and Distortions on the market. As used by many professionals on tour this proves to be a rugged pedal. *** Please note *** The expression input will only work with Stone Deaf EP-1 expression pedal.