a IBM European Speech Research Vangerowstrasse, 18 D-69115 Heidelberg, Germany b NOKIA Research Centre, Itämerenkatu, 11-13 Fi-00045 NOKIA GROUP Germany c IBM Hellas Kifisias 284 GR-15232 Chalandri, Germany d University of Duisburg Lotharstrasse 65 D-47048 Duisburg, Germany |