What are the various physical processes that determine the pitch and tone of a person’s voice? Exactly what goes on in the throat when we sing that is different to when we speak normally?
I would guess more energy is used, but other than that I don’t know.
The only real difference between when we’re talking and when we’re singing is how long we hold the individual tones. Even English is something of a tonal language; not so much as the asian languages, but still, you can tell from various inflections whether someone’s asking a question, laughing, pissed, whatever. So, when we sing, we hold the tones out longer than when we talk. Everything else works pretty much the same.
It’s all a matter of scale.
So you mean no substantial physical changes take place (in the gullet) whilst we are singing save for holding on to the tone of your voice?
What do you mean? I don’t quite understand this part. Please clarify.
So you mean no substantial physical changes take place (in the gullet) whilst we are singing save for holding on to the tone of your voice?
What do you mean? I don’t quite understand this part. Please clarify.
How much the chords vibrate, and how we make them vibrate, works the same way whether we’re talking or singing. When singing, there’s more control over exactly what pitch is produced.
Now, there’s plenty of difference in the mechanics of singing badly and singing well, but between talking and bare-bones singing, not so much difference.
It’s like the difference between walking, and walking while carrying something clumsy and fragile. You’re doing mostly the same stuff, you’re just using more control and paying more attention to the fine points.
Okay, so if you would be so kind as to enlighten me on the observed differences between singing badly and great, I would much appreciate it. Just why do “good” singers sound so… well… good?
It’s a combination of timbre and tonality. Sometimes, one of those can be so great or interesting as to “offset” the other. Bob Dylan, for example, has a great timbre but can’t carry a tune. Joe Cocker, on the other hand, has an ingratiating timbre but is quite melodic.
You use that word – ingratiating. I do not think it means what you think it means. 
But the point is well-taken. Speaking artistically and not scientifically, the difference between speaking and singing is one of perception. There is no major difference in the mechanics, as has been said, but one is perceived as melody and the other as speech. I love listening to a melodic SPEAKING voice, though, so I enjoy the melody of a nice voice … whether speaking or singing.
As a slight hijack, I’d like to see an analysis sometime of what the characterstics of a voice are that cause us to perceive it as more operatic, more rock-ish, or more country-western. Most of us can recognize it, but could we define it?