MFCC flaws

[Roy Patterson <rdp1@xxxxxxxxx>]

Hello all,

MFCC's have, what seems to me, a fundamental flaw, quite 
separate from anything to do with the Mel scale.
The problem was pointed out to me by Alain de Cheveigne. The 
Cepstral Coefficients are COSINE coefficients which means 
that they cannot shift with speaker size to capture the 
shift in formant frequencies that occurs as children grow up 
and their vocal tracts get longer. This is a big effect 
which has been repeatedly observed. See Lee et al. (1999) or 
Voperian et al. (2007) for examples.

We recently presented a paper explaining why recognizers 
trained on the data of a man cannot possibly be expected to 
recognize the speech of a woman, let alone a child. The CCs 
for a given phoneme are different for men, women and 
children. This is one of the reasons that training sets have 
to be so large and training has to take so long.

The paper was presented at Acoustics08 in Paris. The paper 
also describes an alternative, set of auditory features that 
are largely scale invariant.  The reference is

Monaghan, J. J. M., Feldbauer, C., Walters, T. C. and 
Patterson, R. D. (2008) “Low-dimensional, auditory feature 
vectors that improve vocal-tract-length normalization in 
automatic speech recognition,” Acoustics08, Paris, paper 
H000688.

I can provide a pdf of the paper on request, and I would be 
interested in your comments on the ideas in the paper.

Regards Roy P

--
* ** *** * ** *** * ** *** * ** *** * ** *** *
Roy D. Patterson
Centre for the Neural Basis of Hearing
Department of Physiology, Development and Neuroscience
University of Cambridge
Downing Street, Cambridge, CB2 3EG

http://www.pdn.cam.ac.uk/cnbh/
phone: +44 (1223) 333819 office
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