4-Band Analog Stereo Equalizer. Stereo Link and Precise Control Range. It all started with Bob Katz’s idea of tweaking his own xfilter. So Ruben surely took this pretty serious and spend some time for tweaking components on the circuit board until he and of course Bob were 100% convinced with the overall sound by checking serval recordings in our elysia Class-A Lounge – Studio in Nettetal, Germany. Now the result: The xfilter Mastering Edition is a very sophisticated, handcrafted analog stereo 4-band equalizer, with both channels linked for stereo operation. All four bands provide a precise control range of +/-5dB. This fine Stereo Mastering EQ produces the high-end sound of a Class A equalizer at an amazing value for the money. He produces an absolutely precise stereo image based on the use of computer-selected components with extremely low tolerances.