Articulatory perturbation of pitch in singers deprived of auditory feedback

Ideal intonation i n choir singing requires a high accuracy regarding fundamental frequency. Experience of choir conductors suggests that manipulation of the vowel timbre sometimes affects intonation. Articulatory changes, such as shifting the shape of the toungue body, might affect pitch. I n the ideal case a singer would detect such a pitch effect by auditory feedback and compensate for it accordingly; however, poor auditory feedback is known to occur i n choral practise. Singer subjects wearing headphones with noise masking the auditory feedback were asked to change the sung vowel while maintaining a constant pitch. The associated changes of phonation frequency were analyzed. The vowels /i/ and /y/ were found to raise the fundamental frequency. The effects were found to be larger i n the absence of auditory feedback. Introduction b u r a t e control of voice fundamental frequency (@) is a primary technical concern for choir singers. I n a previous investigation (Ternstram & Sundberg, 1982), it was found that the intonation of the individual singer may be affected by certain properties of the sound from the rest of the choir. Absence of vibrato, strong high partials, and prominence of the common partials i n a consonant dyad ( f i f th and major third) were found to facilitate beat-free intonation. Given the mechanical complexity of the voice organ, a change i n articulation is likely to affect also the fundamental frequency. The "intrinsic pitch of vowels" is i n fact a well established concept among speech researchers. A singer, on the other hand, is likely to avoid such effects by means of auditory and/or proprioceptive feedback. In practice, however, the auditory feedback may be poor or even absent. The purpose of the present study was to investigate the influence of articulatory movements on fundamental frequency i n experienced choir singers. Subjects singing with and without auditory feedback were asked to change from one vowel to another while attempting to maintain a constant pitch. The six subjects (two female, four male) were students of Choir Leader Pedagogy a t the State Academy of Music in Stockholm; they a l l had formal vocal training. The experiment was made a part of their course in Voice Acoustics. The subjects sang both with and without masking of the auditory feedback. The feedback was effectively eliminated by means of noise presented over headphones (cf. Elliott & Niemoeller, 1970). An appropriate masking was achieved at a comfortable masker SPL by band-pass filtering the noise. A short written description of the experiment was given in advance. The subjects were instructed to sing the two consecutive vowels in a given vowel pair at a comfortable loudness and pitch, and, in particular, to attempt to maintain the same pitch regardless of the vowel change. Rne subjects were recommended to imagine the pitch in advance, and to make fairly rapid vowel shifts. They were instructed to start singing the vowel pair as soon as they heard the masker noise, and to stop before the noise was terminated after 5 seconds. The vowel pair was then to be repeated without masker noise. There was no prior practice. The vowel pairs were chosen so as to involve changes in only a few articulatory parameters. Thus, pairs 1-3 (see Table I) are back vowels and involve a lowering of the jaw. In pairs 4-6 the jaw is lowered and the shape of the tongue body is changed. Pairs 7-9 involve lip spreading mainly. Pairs 10-12 require a raising of the tongue body. The subjects were given a list with the vowels in CVC key words with the vowel characters underlined. Each subject made two runs separated by a pause of about one hour. Each run lasted for two and a half minutes. In the second run, the word pairs were reversed to give transitions between the same vowels as in the first run, but in the opposite direction.