A signal processing apparatus for changing the frequency characteristics of an input signal, e.g.--a video or audio signal, allows a signal to pass through a transmission circuit in a positive time sequence and then, allows the signal to be transmitted through another transmission circuit having the same transmission characteristics in a reverse time sequence with respect to the positive time sequence. Also, while the transmission circuit is arranged to have a zero-phase characteristic, each segment of a continuous signal is processed throughout a period which is equal to at least two times a duration of an impulse response direction of the transmission circuit. Accordingly, unwanted wave errors appearing at discontinuous regions of the signals are eliminated.