Piero Cappuccilli (baritone) demonstrates the difference between the scientific musical pitch of A=432 (the so-called "Verdi tuning") and the higher, unnatural pitch of A=440. In this example, he sings a part of "Il balen del suo sorriso" from "Il Trovatore" by Giuseppe Verdi.
In this aria, the baritone is forced by high tuning to incorrectly pass the register before the E-natural, as a result of the effort on his vocal cords. Cappuccilli gives this example twice, first singing with the piano tuned to A=432, and not passing register, as Verdi wanted, and then with the piano tuned to A=440, indicating to the audience with his hand when the early passage occurred on E-flat. "Watch out for those E-flats," he said before singing it.
Recorded at the Schiller Institute conference on Tuning and Registration; Milan, Italy; April 9, 1988.