THIS IS A NOT A 500 SERIES RACK, THIS IS FOR TONELUX V-RACK

The Tonelux EQ4P is a DISCRETE Parametric Equalizer with some very unique features. Notice that the panel has no Q control. The filter Q control is in relation to the Boost and Cut control, and uses a "Constant Energy Curve" that keeps the bandwidth wider at lower boost or cut levels and becomes narrow at higher boost or cut levels. This is musically pleasing. The curve is identical to many classic equalizers and is one of the reasons they are preferred over newer designs. When the PEAK button pressed, the 3 yellow "peak" buttons keep the width at a constant 1/3 octave for more precision control. 

The High Frequency has a Shelving button instead of a Peak button. Since the Constant Energy Curve is so broad in the lower frequencies, there is no need for a low frequency shelf button. 

With 4 bands of controls, each of the lower 2 have slightly different frequencies, allowing the lower band to go to 16 Hz, and the upper 2 bands are identical. The IN button is a silent IN/OUT button that does not bypass the unit, but it bypasses the filters.