1. Beckman , Mary E. Ayers Elam , Gayle 1997 Guidelines for ToBI Labelling (Version 3) http://www.ling.ohio-state.edu/research/phonetics/E_ToBI/
2. Boersma , Paul Weenink , David 2009 Praat: doing phonetics by computer (Version 5.1) http://www.praat.org/
3. Asking More Than One Thing at a Time