I have time series of 3 signals, and I found the amplitude of vibration waveform would display the so-called beat phenomenon, which means the amplitude at different time is not always equal, and the beat envelope is also different.
The time history of these signals looks like

It seems that the signal-1 has quick and strong periodic beat, signal-2 has slow and periodic beat, while signal-3 has slow but random beat. So I am wondering is there any indicator to quantify this beat phenomenon of amplitude, like "kurtosis" and "skewness" to measure the peak shape and symmetry of waveform.
And another question is some waveform is not perfectly sinusoid, and again, is there any method to measure the deformation degree of waveform?
Thanks!