Musical theater and opera singing--why so different? A study of subglottal pressure, voice source, and formant frequency characteristics.

The considerable voice timbre differences between musical theater (MT) and western operatic singers are analyzed with respect to voice source and formant frequencies in five representatives of each singer group. Audio, subglottal pressure (P(sub)), and electroglottograph (EGG) signals were recorded while the subjects sang a sequence of [pae:] syllables starting at maximal vocal loudness and then gradually decreasing vocal loudness. The task was performed at each of two fundamental frequencies (F(0)), approximately one octave apart. Ten equally spaced P(sub) values were then selected for each F(0). The subsequent vowels were analyzed in terms of flow glottograms derived by inverse filtering the audio signal, which also yielded formant frequency data. Period time (T(0)), peak-to-peak pulse amplitude (U(p-t-p)), and maximum flow declination rate (MFDR) were measured from the flow glottograms while closed quotient Q(closed) (T(cl)/T(0)) was determined in combination with the differentiated EGG signal. Also the relationship between the first and the second harmonic in the spectrum (H(1)-H(2)), the amplitude quotient (AQ), that is, the ratio between U(p-t-p) and MFDR, and normalized AQ, that is, AQ normalized with respect to period time was calculated as well as the sound pressure level. The results showed that both the MT and the opera singers varied their P(sub) systematically, approximately doubling P(sub) for a doubling of F(0). For a given value of P(sub), the MT singers produced higher values of MFDR, U(p-t-p), and Q(closed), and lower values of H(1)-H(2), indicating a weaker fundamental. Further, the MT singers showed higher formant frequencies and did not show the opera singers' characteristic clustering of F(3), F(4), and F(5).