The three analog signal types are the DC signal, the time domain (or AC) signal, and the frequencydomainsignal.
三种模拟信号分别为DC信号，时域(或ac)信号，以及频域信号。
2
It is normal to use the FFT method to analyze signals. This method is one kind of mathematical method that changes the time domain signals to frequencydomainsignal.
However, the information extracted from a frequencydomainsignal is based on the signal frequency content, as opposed to the shape or time-varying characteristics of the waveform.