From Wikipedia:
Vocal style
Jackson sang from childhood, and over time his voice and vocal style changed noticeably, either through puberty or a personal preference to align his vocal interpretation to the themes and genres he chose to express. Between 1971 and 1975, Jackson's voice descended from boy soprano to androgynous high tenor.[169] In early 1973, the singer adopted a "vocal hiccup", first heard in the song "It's Too Late to Change the Time" from the Jackson 5's G.I.T.: Get It Together album.[170] Although, Jackson did not employ the hiccup fully until the recording of Off the Wall; its usage can be seen in full force in the "Shake Your Body (Down to the Ground)" promotional video. The purpose of the hiccup—somewhat like a gulping for air or gasping—was to help promote a certain emotion, be it excitement, sadness or fear.[11] With the arrival of Off the Wall in the late 1970s, Jackson's abilities as a vocalist were well regarded; Allmusic described him as a "blindingly gifted vocalist".[154] At the time, Rolling Stone compared his vocals to the "breathless, dreamy stutter" of Stevie Wonder. Their analysis was also that "Jackson's feathery-timbred tenor is extraordinarily beautiful. It slides smoothly into a startling falsetto that's used very daringly".[155] 1982 saw the release of Thriller, and Rolling Stone were of the opinion that Jackson was then singing in a "fully adult voice" that was "tinged by sadness".[158]
The release of "Bad" in 1987 displayed gritty lead vocals on the verse and lighter tones employed on the chorus.[14] A distinctive deliberate mispronunciation of "come on", used frequently by Jackson, occasionally spelt "cha'mone" or "shamone", is also a staple in impressions and caricatures of him.[174] The turn of the 1990s saw the release of the introspective album Dangerous; here Jackson used his vocals to intensify the split themes and genres described earlier. The New York Times noted that on some tracks, "he gulps for breath, his voice quivers with anxiety or drops to a desperate whisper, hissing through clenched teeth" and he had a "wretched tone".[162] When singing of brotherhood or self-esteem the musician would return to "smooth" vocals.[162] "In the Closet" contained heavy breathing and a loop of five scat-sung syllables, whereas in the album's title track, Jackson performs a spoken rap.[159][162] When commenting on Invincible, Rolling Stone were of the opinion that—at the age of 43—Jackson still performed "exquisitely voiced rhythm tracks and vibrating vocal harmonies".[175] Nelson George summed up Jackson's vocals by stating "The grace, the aggression, the growling, the natural boyishness, the falsetto, the smoothness—that combination of elements mark him as a major vocalist".[159]
http://en.wikipedia.org/wiki/Michael_Jackson#Vocal_style
