So, if you will open your Lucia score to the “Regnava,” you’ll see several spots, particularly in he second stanza, where the vocal line turns down to D and C on those chest-friendly open vowels (“vedea,”) or even launches little flights from there (“sangue rosseggiò”). These aren’t dainty moments. They are important expressive points along a suspenseful narrative route, and Donizetti surely wrote them in the expectation that in any decently formed Italian soprano instrument, the voce di petto would provide the necessary projective strength and inflectional variety. But in Netrebko’s rendition, the chest either makes no appearance or only a carefully mixed (“blended, shaded, covered“) one. You’ll hear that, I’m sure. Netrebko is a sophisticated artist with a beautiful voice, so nothing will bother you aesthetically about this, at least on a recording. But functionally speaking, it tells us that she feels that engaging the defined chest at these points would not be a comfortable choice. And we don’t have to refer to a larger, more dramatic voice (e.g., Callas’) to hear the difference, but only to any number of pre-1925 Italian true coloraturas (Galli-Curci and Tetrazzini would be top-of-the-line). The Russian soprano I selected for technical comparison, Vera Firsova, didn’t to my knowledge record the “Regnava,” and would have done so in Russian in any case. But if you give her a listen, you will hear the same contrast.

As for the second part of this question, regarding a “letting go” farther up, I’m not sure I can give you a good recorded reference for Netrebko, because I heard it in her voice for the first time in the Tosca I wrote about. Many sopranos experience a build-up of “weight,” or a drag on the free movement of the voice, as they move into the upper-middle range. This happens especially when they are driving the voice in passages of high intensity, or when the music they are singing is heavy for their instruments to start with. It’s a meaty-sounding area in full-bodied voices, so composers set lots of important phrases there, and it’s easy, with repetition, for a voice to acquire some sludge in this tessitura, inhibiting the freedom of the upper range. Among the common (but, in my judgment, imperfect) ways of dealing with this is to “cover” the tone—that is, to darken the vowels, so as not to continue driving the voice from the same position. This is different from simply keeping the tone gathered (“raccolto”). It carries with it a positional shift, a “turning over” of the voice’s posture. But Netrebko’s voice is already turned over, covered—hence her prevailingly dark vowel forms. The strong, balanced bond with chest, which would have brought her voice into a set closer to the ideal, does not exist. Unable to “cover the cover,” she instead simply releases into a suddenly lighter adjustment (we heard this several times on ascending phrases in Tosca, particularly in Act 1). That allows her to continue upward, but not with the same tonal body, and thus unsatisfyingly. For more discussion of this aspect of technique, see my posts of Sept. 29 and Oct. 13, 2017, “Lotte Lehmann and the Bonding of the Registers.”