In order to document the voices in their most characteristic, habitual functions, our protocol consisted largely of familiar exercises that might routinely occur in lessons, such as scales, arpeggios, onsets and sustained notes. However, we also asked our subjects to perform an aria of their own choice as they would in an audition, thus taxing their abilities to the extreme for one part of the protocol. In these figures we look at two spots where the auditors would be expected to listen particularly carefully to the voice production.
The first figure (above) is the big high note (F5-sharp) in the phrase "Prends garde a toi," coming at the final cadence of Carmen's first aria. What we can see here is an evenly sustained note with a well-formed singer's formant that has a moderate sound pressure level, about 15 dB below the dominant first harmonic. This singer's formant is presumably composed of the third and fourth formants working synergetically to enhance the fourth harmonic. The vibrato characteristics of the note are also apparent and will be addressed below.
The second figure (above) comes from the end of the showy coloratura aria "Ah, non giunge," from La Sonnambula and includes both a trill on an F5 (700 Hz) and a penultimate super-high F6 (1400 Hz). In the upper panel the F5 shows a well-formed singer's formant on the trill. The F6 is sustained at a relatively high sound pressure level.
Both these figures offer good opportunities to make observations about the vibrato patterns displayed. The higher harmonics of the spectrogram allow easy calculation of the average period/frequency of the vibrato cycle, as well as the extent of its excursions. The vibrato in the first figure has a rate of 5.5 Hz, well within the acceptable range, but the extent is measured at 16%, above 2 1/2 semitones, which many authorities would consider excessive.
The second figure shows three differing vibrato patterns. That of the final note has a frequency of 5.5 Hz and and extent of 9%, or 1 1/2 semitones. The trill has an increased rate of 6.6 Hz and a greatly increased extent of nearly a perfect fourth. The super-high F6, unlike a note nearly so high (E6-flat) earlier in the aria, has an evidently constrained and slightly irregular pattern at the 6.6 rate.
Vibrato (or the lack of it) is one of the most important elements in the aesthetic impression a voice makes, but subjective impressions of vibrato are often divergent and notoriously imprecise. Objective data on characteristic vibrato patterns, together with their variations, can present valuable feedback for guiding the development of an individual voice.