In a method of selecting a suitable noise suppression component, an input signal to a digital circuit including a transmitter IC, a noise suppression filter, a transmission line, and a receiver IC is expanded by Fourier expansion so as to express the input signal in terms of a series sum of sine waves. The Fourier-expanded input signal and the circuit constants of the digital circuit are used to calculate a signal on the input side of the receiver IC. Similar calculation is performed for all possible filters to assign scores for each of fundamental and harmonic components of the signal, while considering both the noise suppressing effect and the signal waveform quality. Total scores are calculated, and the filters are ranked from a high score to a low score.