From modules manual:

In effect, this module is less like a filter and more like a repeating delay line. It is called an allpass filter because it has the unique characteristic of having a FLAT frequency response. This enables a user to cascade several allpass filters in series without generating excess coloration of the sound. This technique is typically used in reverberators to generate diffusion, a dense grouping of echoes.

Is there a chance you want the notch filter effect?