What is the transfer function of a filter? What is the transfer function of a filter? The transfer function shows how a filter affects the phase of input components as a function of frequency. It is defined as the output phasor divided by the input phasor as a function of frequency. The transfer function shows how a filter affects the amplitude and phase of input components as a function of frequency. It is defined as the input phasor divided by the output phasor as a function of frequency. The transfer function shows how a filter affects the amplitude and phase of input components as a function of frequency. It is defined as the output phasor divided by the input phasor as a function of frequency. The transfer function shows how a filter affects the phase of input components as a function of frequency. It is defined as the input phasor divided by the output phasor as a function of frequency.