It is a curious fact that the neural systems we use to speak are not the same ones that we use to sing, or recite poetry.
The switching from one system, in which tone of voice is not strictly controlled, to the other, seems to be one of the cues people use to detect when someone is lying. Why place a medium capable of expressing one’s emotional state under control if you’re not hiding something?
Learning how to ’sing’ while maintaining an otherwise normal voice is probably one of the skills politicians and other professional liars find it necessary to cultivate.