I would not be surprised if soemone told me he took voice lessons or, at least , took advice from the more serious vocalists he crossed paths with throughout his career. His voice got better and better until his last days. His range got wider and his tone got richer.

I knew he was the "skinny m'fer with the high voice" but I didn't know his voice was "skinny," too.

getwild180 said:

Maybe because he started to sing a little louder? I'm sure many of his fans notice how his voice sounded skinnier and lighter from his first two albums.

He tookl vocal lessons from Seth Riggs, the same vocal coach MJ and Madonna went to. That's why his falsetto was stronger and he was able to sing stronger in his regular and lower registers as the years went on.

getwild180 said:

Maybe because he started to sing a little louder? I'm sure many of his fans notice how his voice sounded skinnier and lighter from his first two albums.

Surely you mean the opposite.

From his first album (starting with the vocalised 'For You') Prince always had a variety of singing genres and pitches depending on the song, and often used different octaves within a song.

That never changed.

Keep in mind also that a good singer will alter the timbre of their voice to match what kind of sounds they're singing with. Those 1st two albums were very slick, and so was P's voice. Dirty Mind was rougher-edged, and Prince sang to match.

Even within one album it'll change. Cue up Condition of the Heart, Raspberry Beret, and Tamborine, for instance.

purplethunder3121 said:

I knew he was the "skinny m'fer with the high voice" but I didn't know his voice was "skinny," too.

Honey, it's something new every day, ain't it?

I think the real shift happened circa 1999. From 1982, he sounds like he's finally in full control of his lower register.
I remember being surprised when "Moonbeam Levels" began circulating: "Hey! That's the 'Purple Rain' (album) timbre!".

Controversy marks the departure from the prominent falsetto.
But the lower register still sounds a bit "adolescent".

Still, CherryMoon57 is right: he had a very wide range from the very start,
"For You" the song being the most obvious example.
The '77-'78 outtakes confirm that.

Maybe if he chose to stay with the falsetto on purpose,
just for the surprise effect: "Wait until I'm ready to play a proper baritone: that'll knock'em out!".
Also, the falsetto was his first and main androgynous statement.
Really clever, if that was the intent.

Also, keep in mind that he may have found at some point the proper combination of microphone and preamp.
Prince's sound is tied to the evolution of studio gear.

[Edited 10/17/17 13:42pm]