Objective: Teachers of singing often observe that students have or perceive difficulties in singing certain vowels on certain pitches. There seems to be no consensus among singing teachers regarding what vowel/fo combinations tend to cause such difficulties. One possibility is source-filter interaction, likely to occur when the frequency separation between a partial and a formant is narrow. Another possibility could be the constellation of tongue position, glottal adduction and vocal fold lengthening. Both these possible causes should be reflected in terms of formant frequencies and/or voice source characteristics. The present study aims to elucidate underlying phonatory and resonatory causes.

Method: Female and male non-singer instrumentalists will be asked to sing both ascending and descending scales through the passaggio regions using different vowels. Both audio and EGG signals will be recorded and analysed with regard to: pitch fluctuations; perturbation measures; and frequency distances between formants and spectrum partials. In addition, participants as well as expert listeners will assess perceived phonatory effort, and higher scores will be used to predict corresponding acoustic and EGG parameters.

Results and Conclusions: According to the theoretical framework of voice acoustics and our previous studies with trained singers, the vowels /u/ and /i/ often cause difficulties in terms of vibrato unevenness and source-filter interaction. However, historically, many voice pedagogues have pointed out difficulties associated to the vowel /a/. The results should shed light on what combinations of resonatory and phonatory conditions tend to cause difficulties for student singers. Knowledge of these combinations should be of great value for the teaching of singing.