R. op den Akker, H. Bunt, S. Keizer, and B. van Schooten. Proceedings of Interspeech 2005---Eurospeech: 9th European Conference on Speech Communication and Technology. Lisbon, Portugal, page 2793--2796. (2005)
D. Sonntag, and M. Möller. Proceedings of the International Conference on Knowledge Management and Information Sharing (KMIS), Madeira, Portugal, (2009)