How to interpret the sign of a cepstral coefficient? I feel like I've got a decent intuition for what the magnitude of a cepstral coefficient represents (i.e. how much of the signal's energy is contained in harmonics of a given wavelength), but I don't really understand what the sign of the cepstrum represents. I feel like it's important to know since some speech processing applications take the max of the real part of the cepstrum (see here), and I'm wondering if there's a reason why the max is in any way more informative than the min, or if I should instead be taking the max of the absolute value of the cepstrum?
For the zero-th cepstral coefficient, the sign is probably always positive since it represents the average energy of the entire spectrum.

For higher-order coefficients, seeing that the question was first posted in 2017, does the OP maybe already have an answer? Would be interested to learn.