Digital filter, filter processing method, and recording medium

A filter processing method including:

• generating, by a separation circuit, from a first complex signal in a frequency domain output to the separation circuit, a second complex signal and a third complex signal being a complex conjugate of the second complex signal;
• performing switching by selecting, by a signal selection circuit, from among a plurality of types of complex signals having different amounts of change in signal amplitude, at least one of a fourth complex signal and a fifth complex signal, by using the second complex signal and the third complex signal which are output to the signal selection circuit by the separation circuit;
• performing filter processing, by a first filter, on the fourth complex signal by a first filter coefficient, and generating a sixth complex signal;
• performing processing, by a second filter, on the fifth complex signal by a second filter coefficient, and generating a seventh complex signal;
• and
• combining, by a combining circuit, the sixth complex signal and the seventh complex signal.

A recording medium recorded with a filter processing program causing a computer to execute processing including:

• processing of generating, by a separation circuit, from a first complex signal in a frequency domain, a second complex signal and a third complex signal being a complex conjugate of the second complex signal;
• processing of performing switching by selecting, by a signal selection circuit, from among a plurality of types of complex signals having different amounts of change in signal amplitude, at least one of a fourth complex signal and a fifth complex signal, by using the second complex signal and the third complex signal;
• processing of performing filter processing, by a first filter, on the fourth complex signal by a first filter coefficient, and acquiring a sixth complex signal;
• processing of performing filter processing, by a second filter, on the fifth complex signal by a second filter coefficient, and acquiring a seventh complex signal;
• and
• processing of combining, by a combining circuit, the sixth complex signal and the seventh complex signal.