@InBook{JesusJackson_ProPor08,
  author = 	{Jesus, L.M.T. and Jackson, P.J.B.},
  title = 	{Computational Processing of the Portuguese Language},
  chapter = 	{Frication and voicing classification},
  publisher = 	{Springer -Verlag},
  address =	{Berlin},
  year = 	{2008},
  month = 	{Sept.},
  editor = 	{Teixeira, A. and Lima, V. and Oliveira, L. and Quaresma, P.},
  pages = 	{11-20},
  abstract = 
"Phonetic detail of voiced and unvoiced fricatives was examined using 
speech analysis tools. Outputs of eight f0 trackers were combined to give 
reliable voicing and f0 values. Log-energy and Mel-frequency cepstral 
features were used to train a Gaussian classifier that objectively labeled 
speech frames for frication. Duration statistics were derived from the 
voicing and frication labels for distinguishing between unvoiced and voiced 
fricatives in British English and European Portuguese."
}
% http://www.springer.com/computer/artificial/book/978-3-540-85979-6