> it sounded like they slowed his voice down a
> little to give it more deep tones. It comes
> off sounding a bit unnatural.

Back in the old days that's what they would have done.

But nowadays they don't have to slow it down. They can modify the voice in all sorts of ways just by pushing a few computer keys.

I have software that can correct the singing of someone who sings totally off key, without affecting their voice at all. (provided it's not too far off).

They even have effect modules that can correct notes in realtime for live performances so that every note is right on key.

And in studios they can digitally totally replace one person's voice with another's, without affecting the speech or singing at all. So that Tiny Tim could sing with Johnny Cash's voice.

A lot of recorded music has been seriously tinkered with nowadays.