answered scientifically long before I started thinking them.
Not surprising - the trick for a layman is of course to find all
the research. Much of it is not available via the web, unless
you belong to a participating research institution. If I were
to park myself in a library, I might have better luck...
However, I did find this:
Emotional Expression Code in Opera and Lied Singing
(Presented by Dr. Eliezer Rapoport at the 1996 Israel
Musicological Society Annual Meeting)
The author has run computer analyses of recordings
of great artists: Callas, Caballe, Margaret Price, Pavarotti,
Kraus, et al, and has performed a systematic breakdown
of how these singers vary their voice and musical expression
in order to express appropriate emotions. The article lists
some 50 different indicators. I have yet to read it thoroughly,
but here is an extract:
This sort of thing appeals to my engineering brain. (-:
A higher degree in excitement than in the C or R modes is achieved by introducing a third element: pitch transition; a gradual increase in pitch in one or two stages from the onset to the sustained stage, mostly practiced by tenors. This is not
singing off-tune but is a deliberate way of shaping the tone, endowing it with some extra qualities: openness, brightness, life, timbre embellishment, and expressiveness. These are the qualities that bel canto tenors use in expressing love, exhilaration and happiness. (The tenor is the hero and the lover in Italian operas). T modes are perceived as a timbre effect. After becoming aware of it the trained listener can discern this gradual transition as a pitch effect. Figure 5 displays an example of the T1 mode taken from the aria "La rivedra nell'estasi..." from Un Ballo in Maschera by Verdi, sung by Luciano Pavarotti, expressing love (marked in Performance
Score No. 3). The aria "De miei bollenti spiriti" from La Traviata by Verdi, and the preceding recitative, express great happiness. Pavarotti and Alfredo Kraus use the T1 and T2 modes extensively in this aria. Further on in the aria at the climax of happiness, the phrase "io vivo quasi in ciel" is repeated five times, each time leading to a climax - sung by Kraus in the T1 mode.
A technocratic, optimistic spin on this might be that, given
such wonderful analysis tools, and the ability to describe
exactly what is going on in these wonderful performances,
we should be able to resurrect, and perhaps even improve
the old magic.
The only remaining problem is of course to attract singers
that are talented enough, and devoted enough, to subject
themselves to the years of training that will still be required.
(Actually, I think that isn't a problem, because lots of talented
and devoted singers do this today. As with many other fields,
the trick is to integrate research into the teaching and wide
practice of the art. Most singers I know will probably be
slightly put off by discussions on Fast Fourier Transforms,
vowel formants, vibrato periods and unit pulses...)