All-pass Network / Filter

An electrical circuit with a uniform amplitude response versus frequency response, but with a phase-shift which does not vary in a linear relationship with frequency. (A pure time-delay device such as a digital delay line will have a phase-shift which is directly proportional to frequency, i.e., its phase-shift increases at a constant rate with frequency.) Complex filters often have significant phase distortion because they are not phase linear, and an all-pass network can be designed to correct phase anomalies without affecting the amplitude response.