Recent research interest has been focused on effectively representing phonatory ability by combining two or more of such quantities as voice intensity (I [dB]), mean airflow rate (U [cm3/s]), and fundamental frequency (F0 [Hz]).
In this paper, a new parameter called "wave-flow index" (hereafter E') is proposed. The E' is defined as E' [dB]=I-U, where U [dB] =20log(U/U0). The theory and the derivation of E' are presented in detail.
The E' is interpreted as (1) the ratio of voice intensity and flow intensity both represented in the dimension of "energy density", and also as (2) a measure similar to "the strength of turbulence", which is commonly used in fluid mechanics.
Although E' does not show the energy conversion efficiency at the glottis, E' is considered to show a wave efficiency, in the sense that E' is derived from the ratio of the wave component to the flow component in the speech signal radiated from the mouth.
Based on the preliminary data for the normal case and three laryngeal diseases, following results were obtained (1) When normal male and female were compared, neither the location nor the spread of the distribution of E' showed statistically significant difference. This suggests that E' can be used as a common measure for both male and female. (2) Normal range of E' was about 20dB. (3) Among the three diseases, E' becomes larger in the order of the recurrent nerve paralysis (N), the vocal fold polyp (P), and glottic cancer (C). (4) For N, E' was much smaller than that for normal. In the two dimensional display with I and U, N showed a marked increase of U compared with I. This increase of U suggests the incomplete closure of the glottis. (5) For P, E' was smaller than that for normal. This, too, is mainly due to the increase of U, and suggests the incomplete closure, although not as marked as for N. (6) For C, E' was slightly larger than that for normal. This was in part due to an increase of I, suggesting the presence of high frequency noise component.
Since the wave-flow index E' can be easily obtained from a non-invasive measurement, E' would be a useful parameter for clinical examination.
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