Signal processing device and signal processing method

A signal processing device comprising:

• a processor;
• and
• a memory storing a program, upon executed by the processor, to perform a process:
• to acquire an input signal;
• to extract a specific signal by multiplying the input signal by a window function;
• to perform frequency conversion on the extracted signal;
• and
• to output the frequency-converted signal,
• wherein the window function comprises a synthesis of one or a plurality of cosine function terms, and
• the window function is obtained by multiplying a negative coefficient to the cosine function term selected from one or the plurality of cosine function terms so that zero value is set at a center of the window range and a peak power of a sidelobe corresponding to the cosine function term in a frequency domain is reduced, a reduction of a frequency resolution is suppressed, or both thereof more than that of multiplying positive values to all of the cosine function terms.