There is provided a signal processing device which includes a change position detection unit that detects stepwise change positions of an n-bit quantized signal generated from an input signal; a density detection unit that calculates a value indicating a degree of density of the stepwise change positions detected by the change position detection unit; and a first low-frequency component extraction unit that extracts a desired low-frequency component from the input signal based on the value indicating the degree of density of the change positions calculated by the density detection unit.