While watching the battle rounds of THE VOICE with some friends, we were sometimes at a disagreement over which singer was superior. I always won but that doesn't mean I was always right. Listening is in the ear of the beholder. In these reality competitions, sometimes the eye.
I was listening for dynamics, enunciation, good phrasing and singing off the page. Some people would call it soul, or tone and the judges often called it "in the pocket." Randy Jackson used to call it "the 'It' factor." I'll break it down on my personal technical level.
Singing with dynamics is easy to comprehend. The singer gets louder and softer while singing phrases. It adds a contour to the phrase or even the entire song. In this instance I was listening for more inner dynamics. More than within a phrase but, including within a word. If they were singing a vowel on a whole note or a note held for a while, I was listening if they did anything with that note. If they held note at the same volume, I was bored. If they got loud or soft on it, they piqued my interest. One of them evolved the diphthong and that was cool. A diphthong is a vowel which has two vowel sounds such as in the word "eye." A trained singer would sing it sort of like "ahhye" or maybe "ahhhh." "E" is a harsh sound and can cause a singer to lower their soft palate and raise the tongue. What is bad about that is it diminishes a clear, full and open tone. An untrained or maybe a country singer would sing, "ah-eee." Try it yourself. Sing the letter "i" and notice how quickly you want to sing an "ee" and raise the tongue. That's a diphthong.
A second dynamic I listen for is what they do with repeated words. Let's say you fell and broke your leg. You would yell for help. If no one answers, you yell a little louder. No answer? You yell LOUDER. Try it (but softly in case someone hears you). The same thing would happen as you lose hope. You yell "HELP!" Then maybe "help . . . " then "hel . . . " So when one of the singers sang "I love you, I really do love you, yes, I love you." each repetition about love needed to be different every time.
Poor enunciation is, well, singing without consonants. A singer can't be understood and what is the purpose for singing if it is not to share words? In other words, wi ou onso an , ou an' e un erstoo. I zone out on singers who make me work to understand them. If they mumble their lyrics, clearly they are not important to them, why should I listen then?
Phrasing is when a singer takes a breath. It is the commas of the musical line. Some singers can be artistic with this such as Adam Lambert who while competing on American Idol would sing long phrases without taking a breath. I loved that. Others, take lots, of breaths, all over, the, place. For me the worse sin-(breath)-gers are the ones who take breaths in the mid-(breath)-dle of words. Those of you who go to church, listen the next time a soloist sings the song "Ave Maria." Many soloists will sing "A (breath) ve, Mareeee (breath) eee (breath) ya." Cracks me up every time.
Singing off the page is a simple concept. It is nice when a singer adds a run but often, the run is just ornamentation and has nothing to do with the lyric. Too much meaningless ornamentation can be tiresome. I prefer singers who throw in bent notes. These are also known as crushes, scoops, gliss or blues notes. They are notes that are just slightly off pitch but resolve to the correct pitch. It is very satisfying.
Another factor is something called entasis where the singer is just slightly off the beat. This isn't the same as dragging because they only do it on a few beats every few bars. It is a way of accenting words and saying to the listener that these words are important so I am giving them a little more time. Jazz pianist great Erroll Garner was a master at playing off the beat and he would often do it for a whole song. Our brains crave the unpredictability of entasis. Just listen to any MIDI file where the notes are quantized perfectly on the beats and you'll hear how boring perfectly-on-the-beat music can be.
A great performance is often filled with purposeful uncertainty. Those musicians who can do that are called artists. With music, as with all things, your mileage may vary. How perfect is that?