Text from Fulltone's website:
What’s this, another touch-sensitive, dynamic, natural sounding overdrive/distortion to confuse the marketplace?
Nope, this is the Fulltone “Secret Frequency. “Secret Freq.” for short. Although it does the gig-friendly clean boost and OD thing as good as any, it goes well past that when asked to, right into Rock territory while retaining a natural sound.
Dynamic asymmetrical clipping gives the Secret Freq. a sweet, musical clean boost, juicy overdrive, and rich, touch responsive high gain sounds. Not like the PlimSoul, nothing like the OCD, and not like any other pedal, but worth the price of admission were you to use it simply as is for your “bread and butter” OD/Distortion pedal.
But the ‘Freq has WAY more tricks in its bag than your average transparent OD/Distortion... it just may knock a handful of OD/Distortions right off your ’board and straight on to Ebay thanks to another innocent looking knob labeled “Freq.”.
What's this "Freq." knob?
Turn it Clockwise and my proprietary circuit adds as much as 20db of active narrow band juicy MIDRANGE right where it does the most good, it‘s like installing a wah-wah right where the distortion is being generated. But unlike turning on your wah-wah along with a distortion pedal, with the ‘Freq. the bass and treble frequencies don't disappear... Very unique, and not to be confused with a simple active or passive midrange control tacked on to the end of the circuit, as is the case with all other pedals you’ve tried with a “Mid” control. Adding the ‘Freq’s midrange imparts WAY more sustain and lets you easily place the guitar in the mix where you want it, irrespective of volume... soundman's not going to bury you anymore.
What's it sound like?
Along with a slew of basic great OD/Distortion pedal sounds, it allows you to replicate a very, very wide range of your favorite guitar & amp sounds. Remember that when the ‘Freq. knob is fully-counter-clockwise the Midrange enhancement effect is OUT of the picture and the pedal is a truly versatile and natural sounding pretty transparent OD/Distortion! At low to mid overdrive settings, turning the ‘Freq knob up a little gets hammer-of-the-Gods penetrating PUNCH!
At more extreme (clockwise) Freq settings?
Brings a smile to your face an evokes the coolest Jimmy Page, Brian May, Michael Schenker, Robin Trower, Tom Scholz tones that you just couldn’t previously get without a bunch of studio EQ, just the right setting on a great wah-wah, or a slew of British amps. I predict the Secret Freq. is going to become an indispensable part of many guitarist’s arsenals very soon.