Southern Pa-O (S. Pa-O) is a Karenic language of the Tibeto-Burman subgroup of the Sino-Tibetan language family. In Thailand, there is a large S. Pa-O community around Rama II Road. This study aims to investigate the gender variation in acoustic characteristics of S. Pa-O lexical tones. F0 in Hertz based on the biological difference of larynx vibrating rate was converted into semitones to normalize cross-speaker differences. Then, semitone and real time values of 6 lexical tones (4 non-checked tones and 2 checked tones) were used to generate 2nd degree polynomial trendlines to show F0 contours and shapes. 

The results reveal a gender effect on acoustic characteristics of S. Pa-O tones. Differences in F0 characteristics between the male and the female speakers are found in non-checked tones (T1, T2, T3, and T4). The two checked tones (T5 and T6) do not show distinguishable F0 characteristics. The F0 gender characteristics of T1, T2 and T4 show differences between genders in terms of F0 contours. The case of T1 and T2 is a tendency. Regarding T1, the male speakers produce the tone with a falling-rising contour and the females with a rising contour. The F0 contours of the males’ T2 tend to be level while those of the female’s T2 tend to be falling. The gender difference of T4 is dichotomous. The males’ T4 is falling, and the females’ T4 is rising-falling. Despite a similar F0 contour, the T3 of the male and female speakers can be differentiated by the F0 shapes. The F0 shapes of the males’ T3 are all curved, while those of the females’ T3 are linear. All in all, the gender variation in S. Pa-O tones is confirmed in the acoustic study.