Previously, major style-specific aspects of the acoustics of stage voices have been re-examined. In the present project, further clarifications are approched: phoneme and text intelligibility on high pitches; dependence of lower spectral characteristics on fundamental frequency, and formant pattern ambiguity; the effect of style-specific higher spectral characteristics on voice projection; age and gender-related spectral differences; the relationship between vocal tract resonances and spectral characteristics of sounds produced in different styles and at different fundamental frequencies.
Preceding project and corresponding indications – the basis
In a preceding SNSF project, major style-specific aspects of the acoustics of stage voices have been re-examined: extensive F0/pitch variation and formant tuning, increased intensity in mid and high spectral ranges, and singer’s or speaker’s/actor’s formant cluster (SF or SPF). The extensive and systematic recordings consist of utterances of 42 professional singers, actresses/actors, and non-professional speakers. Sounds of the long German vowels /i, y, e, ø, ɛ, a, o, u/ in V, sVsV, and minimal pair condition were investigated with varying basic production parameters such as F0/pitch, vocal effort, production style, and phonation type. Additional references for "average" conversational speech were also created. Acoustic (single sounds) and statistical analyses (sound samples) were conducted. Perceptual vowel quality was investigated in listening tests. In total, a corpus of more than 30'000 utterances of 42 speakers was created in order to build up an empirical reference on the matter.
Up to now, our analyses provide strong indications for the following: (1) Possible vowel discrimination on high pitches up to levels of F0 in the range of 800–1000Hz. Neither spectral undersampling nor oversinging statistical F1 is found to directly impair vowel discrimination. (2) Depending on vowels and F0 ranges, lower spectral peaks and, if determinable, related formants < 1.5kHz often shift with rising F0. These shifts are found for both professionals and non-professionals, and a substantial part of them are indicated to maintain the perceived vowel quality. (3) Visual inspection of the spectra in general confirm findings reported in the literature of increased intensity in mid and high spectral ranges and SF for professionals. However, the methods of acoustic analysis are in need of further investigation. Moreover, the effect of these acoustic characteristics on vowel perception is also in question. (4) Speaker group differences in the vowel spectra < 1.5kHz decrease or disappear when comparing sounds at similar F0 levels.
Need for clarification
On the basis of these indications, major aspects of stage-specific as well as of general voice production and perception have to be addressed: (1) For a clarification of phoneme and text intelligibility on high pitches, additional recordings of comic and voice-over actresses/actors and related listening tests are needed. (2) Clarification of the observed F0-dependence of lower spectral characteristics (of importance for the concept of formant tuning) requires resynthesis, synthesis, and low and high-pass filtering experiments. (3) The acoustic effect of increased intensity in mid and high spectral ranges and the shaping of the spectral envelope > 2.5kHz needs to be clarified requiring additional recordings live on stage, including an additional investigation of SPF. (4) Clarification of the observed F0-dependence of lower spectral characteristics and their impact on expected age and gender-related spectral differences also requires resynthesis experiments. (5) The relation between F0-dependent changes of vowel-specific spectral characteristics and style-specific spectral characteristics on the one hand, and articulation on the other, should be clarified requiring a parallel investigation of sound production and measurement of vocal tract resonances.
The present project
The present project addresses these issues within the following experiments: Additional recordings (in the studio and live on stage in a large concert hall); vowel resynthesis (related to natural vocalisations) and vowel synthesis (related to statistical formant patterns) with extensive F0 variation, testing constancy/alteration of vowel perception; low and high-pass filtering of vowel sounds produced at very different F0, testing constancy/alteration of vowel perception; vocal tract investigation, testing the parallelism between vowel-specific spectral characteristics of sounds produced on very different F0 and articulation.
Listening tests are included in all experiments.
The on-going project also attempts to contribute to the improvement of the methods of acoustic analysis for sounds on high F0/pitches.
Publications of journal papers are intended, and great effort is made for an extensive open access publication (database of recordings and eBook).
Relevance
The present project aims at contributing to the interdisciplinary research on the fundamentals and the aesthetics of the voice.
The empirical basis provided–unique in its systemacy and extension–and the clarifications attempted will allow for in-depth insight into the acoustics of stage voices and into general aspects of voice and vowel acoustics, indispensable for further research and for an assessment of the relevance of acoustical descriptions for vocal education and the use of technical aids on stage.