The BSS DPR901ii is a four band parametric equalizer which varies the degree of equalization dynamically, as the program level changes. The process can be thought of as frequency elective compression and/or expansion, but it is fundamentally different to simple ‘frequency-conscious’ dynamics processing as used for noise gating, de-essing and the like. It is also very different to the growing family of ‘sliding filter’ techniques used in single-ended noise reduction processors.