December 13-15, 2007: Firenze, Italy, ed. by C. Manfredi, ISBN 978 88-8453-673-3 (print) ISBN 978-88-8453-674-7 (online) © Firenze university press, 2007. Abstract: The approximate entropy of vowel phonation spectra has been used to reveal two normal voicing groups in healthy males. An analysis of the corresponding open and closed quotients for the groups shows the first with balanced quotients...