It acts as an imitation of the Kilohearts Disperser , used to "smear" transients.
To truly grasp , you need to understand two concepts: Phase Shift and Group Delay . allpassphase
The phase shift ( \phi(\omega) ) for the first-order analog all-pass is: [ \phi(\omega) = -2 \arctan\left(\frac\omega\omega_0\right) ] It acts as an imitation of the Kilohearts