A signal processing apparatus includes: a clock generator configured to generate a clock signal having a phase based on a phase of an input signal; a phase modulator configured to shift the phase of the clock signal to generate a phase-shifted clock signal; and a signal synthesizer configured to synthesize the phase-shifted clock signal and the input signal to generate a synthesized signal, wherein the phase modulator is configured to determine a value by which to shift the phase of the clock signal based on an amplitude of the input signal and an amplitude of noise included in the input signal.