Cepstrum analysis: how to find quefrency step?

Question

I'm newbie in cepstrum analysis. So that's the question.

I have signal with the length 4096 and sample rate 8000 Hz. I make FFT and get the array with the length 4096*2 (2*i position is for cosinus coeff, 2*i+1 position is for sinus coeff). Frequency step is (sampleRate/signalLength == 8000/4096). So, I can calculate frequency at i position this way: i*sampleRate/signalLength.

Then, I make the cepstrum transformation. I can't understand how to find quefrency step and how to find frequency for given quefrency.

This question appears to be off-topic because it is about maths — Mitch Wheat, Aug 28 '13 at 09:18
But would be right on topic at http://dsp.stackexchange.com/ — Damien, Oct 18 '14 at 05:56

score 2 · Answer 1 · answered Aug 28 '13 at 19:41

The bin number of an FFT result is inversely proportional to the length of the period of a sinusoidal component in the time domain. The bin number of a quefrency result is also inversely proportional to the distance between partials in a series of overtones in the frequency domain (this distance often the same as a root or fundamental pitch). Thus quefrency bin number would be proportional to period or repeat lag (autocorrelation peak) of a harmonically rich periodic signal in the time domain.

Cepstrum analysis: how to find quefrency step?

1 Answers1