One of the most difficult vocal techniques is the ability to hit the high notes cleanly and without blowing out the tone. Even harder is the ability to hit those notes delicately. Here are three fantastic opera performances that show off different ways of hitting the high notes:
First, a classic: 1966 Covent Garden performance of Luciano Pavarotti singing "Ah! Mes amis!" from Donizetti's La Fille du Regiment. Skip to 4:42 if you want the famous bit, where he sings 9 high Cs. The piece was originally written for those high notes to be sorta yodeled, but it quickly became a showpiece for tenors.
Here, Pavarotti absolutely nails the notes with clarity, and while they're a Big Sound, they don't sound overdone.
For something much lighter, we have Michael Spyres singing "A tanto duol" from Bellini's Bianca e Fernando. This piece was written for Rubini, a friend of Bellini's, who had an absurdly range and technique. (This piece is so absurd that it was clearly in the canon of "written for this one dude".)
Listen to how effortlessly Spyres moves through notes like A4, which are normally "high notes" for a lot of tenors. Then he sings a C5 at 4:17 where he just moves through the damn thing like it's nothing. Which makes sense because he hits an F5 later, a note that's high in the alto range.
And then there's the hardest thing of all, which is singing the high notes quietly. Nicolai Gedda's performance of Magische Töne, from Die Königin von Saba by Karl Goldmark, is one of the most remarkable recordings I've ever heard.
The piece isn't a "showstopper", given its slow pace and delicacy, but it's one of the hardest pieces written for tenor. Its instructions are for it to be sung "very tenderly" ("sehr zart"), and Gedda sings it like the music is floating. I've never heard a tenor hit a high C with such delicacy. It's a bit hard to articulate what makes the sound different from an alto singing those notes, but it's there. *
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* @jadagul talks about how Jean Valjean's arias sound "better" when baritones sing them (as opposed to tenors), because the high notes sound hard, even when they're performed with perfection.
For comparison, here is Andreas Scholl, a legendary countertenor, singing "Down by the Salley Gardens" by Benjamin Britten. His range is considerably higher and easier than any of the tenors above, and his notes are even more graceful. But they sound fundamentally different and easier coming from him, because they aren't challenging and are entirely within his tessitura.
