In reference to art as a whole, people have their own opinions on why they prefer a certain painter or a certain genre of music or a certain singer. This is completely natural and entirely understandable. However, that does not negate the fact that their are certain quantifiable elements to any art which demonstrate why it is so valuable. This is also true in music, and in particular for singing.
Since singing is such a personal experience for the artist and also for the listener, there tends to be a general belief that what one likes is just a matter of "preference"; and no one has the right to criticize someone else's preferences. Let me just say that this belief is 100% *WRONG*. Not in the sense that people do not have preferences, but in the sense that *opinion* does not shape reality nor does it alter quantifiable facts. A person with a particular opinion may or may not know these quantifiable facts for whatever reason. So for those who do not know these facts I am going to try and explain what they are in this post. I hope it helps to cultivate your opinions and taste. My ultimate goals here are not just to point out the things that are lacking, but also to give people the tools by which to grow which will greatly enhance their listening experience. This actually allows you to appreciate and enjoy singers in a much deeper and more moving way.
People generally seem to recognize if one singer is better than another singer regardless of musical genre. Not that genre isn't a factor because unfortunately it can be. However, when we are listening for vocal prowess we must learn to differentiate genre preferences from vocal ability. I may not like a certain singer's genre of music; e.g., heavy metal, but I can still recognize if that singer has vocal skill regardless of their musical genre. So for the sake of this article I am going to only write about the things that make a singing voice great.
When someone sings a note, that note is made up of the fundamental pitch as well as the "overtones" or harmonics relative to that pitch. As listeners we mainly hear the fundamental pitch, but if we are to listen carefully we can also hear these harmonic overtones. They are the "ringing" in the sound. That doesn't mean we will be able to hear them distinctly like notes played on a piano, but still we can hear that "ringing" or "clear" quality to the sound. The Italians use the word "squillante" to describe this sound. Squillante literally means, "ringing". Others describe these overtones as "brassy" or some just hear it as clarity or "focus". If you have never had these sounds pointed out to you and "defined" for you this will come as a totally new aural experience. The importance of understanding the fundamental pitch and the harmonic overtones is crucial to understanding what makes one sung sound superior to another sung sound; and consequently what makes a certain singer better than another singer.
In order to help with the idea of harmonics in the voice I think it is beneficial to refer to piano playing. When a pianist plays a single note on a piano we quite obviously just hear that note or fundamental pitch. And a pianist could certainly play a whole song one note at a time, but that would not be very interesting. On the other hand, when a pianist adds "chords" we have a totally different experience. The chords are made up of the fundamental pitch, which gives us the melody, and the other notes in the chord which give us the harmonics. We can think of a great voice and a mediocre or average voice in a similar way. A singer with a great voice is able to sing the melody (fundamental pitch) while also having a clear, "ringing" to their sound. That ringing is the harmonic overtones similar to when a pianist plays a chord. The more harmonics a singer has in their voice the more rich their voice will sound. I call this the "core" to the sound. On the other hand a mediocre singer will have very few if any harmonics in their sound. Furthermore, a singer could have "noise" in their sound. Noise is anything that is dissonant to the fundamental pitch. We often hear these sounds as "screaming", breathy, screechy, tinny, and/or generally unpleasant. All of these things are quantifiable and therefore give clear standards by which we can judge a quality of a singer's voice. This is one of the ways we can determine that the voices of Tebaldi, Caruso, Del Monaco, Gigli, Maria Callas (in her prime), Titta Ruffo etc. are superior to singers of today like Dessay, Villazon, Hvorostovsky etc. There are a few other quantifiable qualities that we can use to determine the quality of a singing voice and I will be expounding on those in part II of this discussion.