Apply a two-pole all-pass filter with central frequency (in Hz) frequency, and filter-width width. An all-pass filter changes the audio’s frequency to phase relationship without changing its frequency to amplitude relationship.

The filter accepts parameters as a list of key=value pairs, separated by ":".

A description of the accepted parameters follows.

frequency, f

Set frequency in Hz.

width_type

Set method to specify band-width of filter.

h

Hz

q

Q-Factor

o

octave

s

slope

width, w

Specify the band-width of a filter in width_type units.