What It Is
The A.R.C.—an acronym for "Articulation, Resonance & Clarity"—provides a unique, niche function by allowing the musician to change the balance of these three characteristics of their instrument(s). Originally designed to help the flagging guitar chops of its designer—by smoothing out the fretting/picking on a beautiful (& undeserved) 1986 PRS Custom—the A.R.C. has found a cult following among acoustic instrument players wanting to experience the "acoustic sound" while playing live with a wide variety of instruments: mandolins, ukeleles, acoustic guitars, fiddles/violins, acoustic basses, lap steel, dobros and the like. One player described the A.R.C. as being able to control, to taste, the resonance of his custom Collings dreadnaught during live gigs, while others have reported finally being able to hear their instrument's true nature through the stage monitors!

How It Sounds
Although the A.R.C. can be used to unnaturally exaggerate certain aspects of an instrument's sound, most generally the sound is operated in a range that sounds natural. Imagine the challenge of playing mic'ing/performing on an instrument whose sustain levels are very low compared to it's percussive characteristics (e.g., a mandolin or banjo) and trying to hear playing nuances without compressing the signal into a lifeless blob! Such is the challenge for many musicians who've found the natural sound of their instruments restored, particularly in a live situation!

How It's Done
At it's core, the A.R.C. is a dynamic processor (a compressor) configured to achieve dynamic/equalization effects. The compressor's sidechain is affected by equalization circuits and is blended with the original instrument signal in varying amounts to achieve the desired effect as a function of its front panel controls.