Time vs Frequency vs Cepstrum

The cepstrum (pronounced KEP-strum or SEP-strum) is a signal processing technique performed on a time-domain signal to look at periodic content in data, such as harmonics, sidebands, and orders.

The cepstrum is sometimes referred to as a “spectrum of a spectrum” because it involves calculating the spectrum of the time signal and then performing another spectral operation. It is calculated by first taking the Fourier transform of a time signal to create a frequency spectrum, converting it to a log scale, and then performing an inverse Fourier transform on the spectrum

A great article from Siemens:

https://community.sw.siemens.com/s/article/Cepstrum-Analysis