This is the legendary Trace Elliot SMX Dual Compressor...very hard to find, and this one is near-mint! It comes in the original box, with the manual and power supply. $100, including shipping to CONUS From the manual: The SMX DUAL COMPRESSOR is two separate compressors in one unit, each compressor has its parameters set to suit the frequency band that it is dealing with i.e. Fast attack for the High frequencies and Slow attack for the Low frequencies. Two input filters are used to split the signal into its High and Low frequency components, the output from these feed the High and Low compressors. The EQ BALANCE control sets a crossfade between the output of the two compressors and provides an extremely versatile and entirely new form of powerful tone control.