On the music player, several vertical columns jump up and down with the music rhythm from left to right, like a bar chart showing the spectrum of the music player; The spectrogram shows the DB distribution from 2Hz to 2 Hz, which can be understood as the loudness distribution, that is, the volume in the common saying. The waveform obtained by fft calculation is sometimes a spectral line, sometimes it is a restored horn power supply voltage signal waveform, and of course it can also be regarded as a sound waveform.

The following figure shows the instantaneous loudness of each frequency. The lower the frequency, the higher the frequency, the higher the treble and the midrange.