Newsgroups: comp.speech
Path: pavo.csi.cam.ac.uk!doc.ic.ac.uk!syma!tapk0
From: tapk0@syma.sussex.ac.uk (Ramsin Alexi)
Subject: Re: A little cepstral question.
Message-ID: <1993May7.122026.27772@syma.sussex.ac.uk>
Organization: University of Sussex
X-Newsreader: TIN [version 1.1 PL8]
References: <MHALL.93May4124551@occs.cs.oberlin.edu>
Distribution: comp.speech
Date: Fri, 7 May 1993 12:20:26 GMT
Lines: 34

Matthew Hall (mhall@occs.cs.oberlin.edu) wrote:
: Hello,
: 	I have heard a lot about cepstral analysis in regards to
: speech processing.  Right now I am just using the results of an FFT,
: for the patterns I create, however I would like to increase accuracy a
: little.  The cepstral is supposed to imitate the way the ear hears,
: which should make recognition accuracy better.

: Here are some questions:
: The cepstral, as I understand it, is begotten by taking the FFT of a
: signal, taking the complex logarithm of each frequency component, and
: doing an IFFT on the result, i.e.
: Cepstral = IFFT(Log(FFT(x))), where x is, say, a real valued sequence.
: Now the FFT takes x from the time domain to the frequency domain, but
: the IFFT takes it back to the time domain.  How do I interperet the
: cepstral in a meaningful way if it is in the time domain?

: Second, for processing concerns, may I disregard the phase info when
: taking the cplx logarithm?  since log(z) = ln(|z|) + i*arg(Z), and
: arg(z) is just the phase, can I simply use log(z) ->ln(|z|), and take
: the IFFT of that, or is that a no-no?

: I have looked at several DSP books, one which covers the cepstral, but
: it isn't very clear about what to do with it (well, I'm not an
: engineer, so I'm not sure about half of what its talking about)

: Thank you for any help you can provide,
: -matt
: --
: -------------------------------------------------------------------------------
: Matt Hall.    mhall@occs.oberlin.edu
:               (216)-775-6613 (That's a Cleveland Area code. Lucky Me)
:   
: "Life's like mayonnaise soda"	-Lou Reed
