Patent ID: 8731856

Claim:
A frequency spectrum analyzing apparatus for performing a frequency spectrum analysis with respect to a detected value of an operating parameter of an internal combustion engine in synchronism with rotation of said engine, said frequency spectrum analyzing apparatus being characterized by comprising: sampling means for sampling the operating parameter at predetermined time intervals, and converting the sampled value to a digital value; element intensity calculating means for calculating intensities of first and second elements with respect to a predetermined number of the sampled values, wherein the first and second elements respectively correspond to a plurality of frequency components contained in the detected value, and a phase of the second element differs from a phase of the first element by 90 degrees; and frequency component intensity calculating means for calculating frequency component intensities corresponding to the plurality of frequencies in synchronism with rotation of said engine, using the first element intensities and the second element intensities, wherein said frequency component intensity calculating means includes offset component calculating means for calculating offset components contained in the first element intensities and the second element intensities, and calculates the frequency component intensities after removing the offset components from the first and second element intensities, said offset components indicating a direct current component contained in the detected value.