Cepstrum - what is it good for?
Cepstrum - what is it good for?
(OP)
Back when I was young and naive I came across Cesptral Nyalysis or whatever silly word game they want to call it. Since then I have occasionally tried it on real signals with strong harmonic structure, and usually found it to be less than helpful. I suppose it is fair to say that I usually have the luxury of looking at variable speed data, so a waterfall or campbell's diagram is helpful and easy to interpret.
Anyway, here's an example of a cepstrum, showing how the presence of noise and pure tones seem to render it less than powerful. The blue signal, which is the useful red one with some noise and tones added, fails to strongly identify the correct harmonic spacing.
Sorry about the axis labelling, apart from the first the x axis is in bins, and the y axis is in whatevers.
So am I missing some trick here?
Anyway, here's an example of a cepstrum, showing how the presence of noise and pure tones seem to render it less than powerful. The blue signal, which is the useful red one with some noise and tones added, fails to strongly identify the correct harmonic spacing.
Sorry about the axis labelling, apart from the first the x axis is in bins, and the y axis is in whatevers.
So am I missing some trick here?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?





RE: Cepstrum - what is it good for?
I'm not suggesting that these things don't work, it's just there are easier (and often more reliable) ways of achieving the same thing.
RE: Cepstrum - what is it good for?
RE: Cepstrum - what is it good for?
- Steve
RE: Cepstrum - what is it good for?
RE: Cepstrum - what is it good for?
- Steve
RE: Cepstrum - what is it good for?
RE: Cepstrum - what is it good for?
The claimed insensitivity to sensor location sounded interesting to me when doing PDm routes with my mag mount accelerometer, but gearboxes are such cranky sammiches that I soon decided the tools should be oil analysis was 75%, and vibration analysis 25% on them.
RE: Cepstrum - what is it good for?
By the by the speech analysis boys call a very similar but totally different analysis cepstrum, they take the IFFT of the log of the magnitude of the orignal FFT, turning it back into the time domain. Matlab seems to offer both options but you need to read the documentation of their various functions carefully.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Cepstrum - what is it good for?
Then when you will apply again the FFT, you will obtain frequencies that correspond the periodicity of your original signal.