Method and apparatus for calculating filter factors

摘要

A transfer function is determined in accordance with an amplitude characteristic and a phase characteristic. The transfer function is subjected to inverse Fourier transform. An imaginary part of a result of the inverse Fourier transform is set to zero and thereby the result of the inverse Fourier transform is converted into a converted result. The converted result is subjected to Fourier transform. The amplitude characteristic and the phase characteristic are updated in accordance with a result of the Fourier transform. Such processes are reiterated. A primary desired amplitude characteristic is corrected in accordance with the finally-obtained amplitude characteristic so that the primary desired amplitude characteristic is converted into a final desired amplitude characteristic. A final desired phase characteristic is determined in accordance with the finally-obtained phase characteristic. A second transfer function is determined in accordance with the final desired amplitude characteristic and the final desired phase characteristic. The second transfer function is subjected to inverse Fourier transform. Filter factors are calculated from a real part of a result of the inverse Fourier transform of the second transfer function. The calculated filter factors are set in a FIR digital filter.