I was an instrumental musician in my early years, and the research I have done about voices recently does not surprise me. Many musical instruments have register keys which alter the resonance frequency of the intstrument. With the human voice, the resonance phenomena lie in different parts of the body. In the case of a falsetto, the nasal passages create the falsetto resonance range. Even basso profundo voices can develop this falsetto range, and it greatly increases the versatility and freqeuncy range of the voice.

Frankie became famous for his falsetto voice, and I guess it typecast him just as William Shatner will always be typecast as Captain Kirk. But you can’t argue with either’s success.