The expression of singing emotion - contradicting the constraints of song

In speech, emotion is freely carried in the fundamental frequency, rate of speech, intensity and spectra of the human voice, although the spectra is largely dictated by words in speech. In singing, however, fundamental frequency and rhythm are constrained by the melody of the song, while the spectra is constrained by the song lyrics. Nevertheless, a large amount of emotion is carried in song; and the same song, with the same melody and rhythm constraints, may be expressed in a variety of emotions. This paper investigates the manner by which different emotions may be conveyed in the human singing voice, given the constraints of song. It goes further to find which subtle variations correspond to which emotion.