A very nice side effect of the topology of the nvelope 500 is that it can also be used as a shelving filter. This is achieved by temporarily deactivating its dynamics sections while keeping the filter stages active.
Freq A now sets the frequency of the high shelf filter, while Attack determines the amount of cut (turn left) or boost (turn right) in this band. Similarly, Freq S sets the frequency of the low shelf filter and Sustain determines the amount of cut or boost.
The special architecture also allows for another nice feature which is kind of hard to find on other EQs: Not only can the two channels be used as two separate equalizers at the same time, but they can be linked for processing stereo material conveniently as well.