Basic FAQ for FFT Analyzer

AC coupling is a first-order high-pass filter composed of a capacitor (C) and a resistor (R), with the main purpose of cutting low-frequency components that include the DC component of the input signal. Its gain characteristics are;

 

（1）

 

This is the case. Here, f₀ is the cutoff frequency of the high-pass filter, and in Ono Sokki's FFT analyzer, it is usually 0.5 Hz. When the frequency of the input signal f is 0.5 Hz (= f₀), the value of equation (1) is approximately 0.707 (-3 dB), and at 1 Hz, it is approximately 0.89 (-0.97 dB).