How Does Speaking Clearly Influence Acoustic Measures? A Speech Clarity Study Using Long-term Average Speech Spectra in Korean Language.

Objectives: To investigate acoustic differences between conversational and clear speech of Korean and to evaluate the influence of the gender on the speech clarity using the long-term average speech spectrum (LTASS).

Methods: Each subject's voice was recorded using a sound level meter connected to GoldWave program. Average long-term root mean square (RMS) of one-third octave bands speech spectrum was calculated from 100 to 10,000 Hz after normalizing to 70 dB overall level using the MATLAB program. Twenty ordinary Korean were compared with 20 Korean announcers with equal numbers of men and women in each group.

Results: Compared with the LTASS of ordinary men, that of ordinary women was lower at low frequencies, but higher at 630, 800, 1,600, 5,000, and 10,000 Hz. Compared with the LTASS of male announcers, that of female announcers was lower at low frequencies. Compared with the LTASS of ordinary men, that of male announcers was significantly lower at 100, 125, 200, and 250 Hz. Compared with the LTASS of ordinary women, that of female announcers was lower at 100, 125, 160, 200, 250, 500, and 10,000 Hz. The LTASS of announcer showed lower levels at 100, 200 Hz and higher at 500, 630, 800, and 1,000 Hz that that of ordinary Koreans.

Conclusion: This study showed that the drop-off of the LTASS in the low frequency region might make the ratings of women and announcers more clearly than those of men and ordinary persons respectively. This drop-off in the low frequency might result in less upward spread of masking and clearer speech. This study reduced an error resulting from a wide variability of clear speech strategies and intelligibility gains, because this study recruited professional speakers. We hope that our results demonstrate the difference in acoustic characteristics of the speech of ordinary Korean persons.