1. A signal-processing apparatus comprising: a first Discrete Fourier Transform unit operable to transform each component in a time window of a series of input signals into a complex number data vector; a vector-multiplying unit operable to perform complex multiplication of the data vector and a coefficient vector for each element, thereby providing a calculation result; and an Inverse Discrete Fourier Transform unit including a real number output portion and an imaginary number output portion, said Inverse Discrete Fourier Transform unit being operable to inversely transform said calculation result, thereby feeding first and second series of output signals out of said Inverse Discrete Fourier Transform unit through said real number output portion and said imaginary number output portion, respectively.