Cepstral Coefficients

[Verity S]

I understand the process of converting a spectrum to a cepstrum. However, I am a little unclear as to what exactly each cepstral coefficient is? If you were to read them off the graph, would you be reading the y-value for the first twelve peaks or simply the y-value for the first twelve quefrency intervals (samples)?

[Simon King]

The latter: simply the y-values of the first 12 points on the quefrency plot.

It might help if you forget for a moment about plotting the cepstrum (which is a slightly odd thing anyway) and just think about the coefficients as a series expansion of the spectral envelope (from a filterbank). They are “shape coefficients”.

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