I have a heard my share of perfect notes from singers in my life. Try American (world famous) tenor Jan Peerce at the end of “Hymn to the Nations” with Toscanini conducting (YouTube). Pavarotti sang many. Eileen Farrell sang a bunch. Also Leonard Warren. Also Galli-Curci. Many others from time to time. I have heard some whole phrases of music sung perfectly. No whole songs or arias sung perfectly, however, from beginning to end. Bottom line is that, as I tell my students, All have “sinned” and fallen short of the glory of God, vocally speaking.” No one is perfect, including me. :*)

Nevertheless, we all keep trying to perfect our singing. I am not always sure we go at it in the right way.
Think about it for a moment. What would we sound like if our voices were perfect?  If we are honest, we have to admit we don’t know. We can describe the qualities and skills we would like to have but can we
actually hear that perfect sound of our own voices in our minds?  Unequivocally, no. Despite this, we often focus our vocal technique on getting the RIGHT sound. How can we possibly direct our voices toward that right sound of which we know little or nothing?  Just to restate, we may well know how beautiful, well-produced voices should sound but that does not mean we know how OUR voices should sound. If I am correct, then you might wonder if it is impossible to change and grow our voices for the better. Fortunately, I think it is not.

The reason it is possible to improve is that the vocal mechanism has an organization – an anatomy and a physiology – that we can work with to improve vocal function.  And, since things that work correctly meet our needs well, if the voice works correctly it will meet our needs, i.e., be beautiful and free in action. I believe that the master teachers of past centuries despite limited knowledge of anatomy figured out how to work with the physiology of the vocal mechanism and were focused on function rather than sound, per se. This is why they discussed registers, types of sound (falsetto, chest, head voice), and how to coordinate these things. Although they heard and described the nature of these individual sounds and the nature of the beautifully coordinated voice, their approach was not to demand the finished product but to manipulate the disparate sounds to make the voice function properly and through that work produce the perfect sound.  My late teacher, Cornelius Reid, used to say that not all attractive sounds are healthy and not all healthy sounds are attractive. I think this is a vital statement in understanding the approach of the bel canto masters. I define bel canto as Reid did, as a functional approach to changing the voice. Through this functional approach, we can take the
not-particularly-attractive sound of the individual registers and coordinate them into a mind blowing, knee weakening, gorgeous and free voice.  The single word that the Italian masters used to describe the perfect sound was chiaroscuro.  Chiaro, clear or bright, signifies the chest voice part of the coordination.
Oscuro, muted or dark, signifies the falsetto part of the coordination. So these two parts of the voice should combine together into the perfect sound. That is bel canto, beautiful song.