# An Acoustic Feature-Based Deep Learning Model for Automatic Thai Vowel Pronunciation Recognition
## 4 Materials and Methods
### Dataset
#### 4.1.4 Exploration of Data  
After the preparation of the Thai vowel dataset, the data for each vowel sound were explored. Table 2 presents the durations of the Thai vowels in males and females: maximum (max), minimum (min), and average (avg).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{5}{c}{**Thai Simple Vowels**} \\ \hline \multicolumn{2}{c}{**Long Vowels**} & \multicolumn{2}{c}{**Short Vowels**} \\ \hline
**Thai** & **Phonetic** & **Thai** & **Phonetic** \\ \hline
01 & /a:/ & os: & /a/ \\ \hline
00 & /i:/ & 00 & /i/ \\ \hline
00 & /u:/ & 00 & /u/ \\ \hline
00 & /e:/ & 100 & /e/ \\ \hline
00 & /e:/ & 100 & /o/ \\ \hline
00 & /x:/ & 100 & /\pi/ \\ \hline \hline \end{tabular}
\end{table}
Table 1: Thai Simple Vowels in the International Phonetic Alphabet (IPA) adapted with permission from Refs. [33,34] Copyright 2015, IEEE.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{5}{c}{**Durations of Each Thai Vowel**} \\ \hline \multirow{2}{*}{**Thai Vowels**} & \multicolumn{4}{c}{**Male Sounds (Seconds)**} & \multicolumn{4}{c}{**Female Sounds (Seconds)**} \\ \cline{2-7}  & **Max** & **Min** & **Avg** & **Max** & **Min** & **Avg** \\ \hline a: & 0.649 & 0.200 & 0.391 & 0.791 & 0.177 & 0.394 \\ \hline i: & 0.616 & 0.161 & 0.357 & 0.667 & 0.175 & 0.395 \\ \hline u: & 0.580 & 0.159 & 0.356 & 0.658 & 0.170 & 0  
The pronunciation of each individual vowel varies individually as well as by gender and age. Even if the same speaker speaks twice, the sound is still different. The values for the duration of 18 Thai vowels are presented in Table 2. For male sounds, the max duration is 0.672 s in / \(\varepsilon\):/, and the min duration is 0.059 s in /a/. The average maximum and minimum durations are 0.391 s in /a:/ and 0.112 s in /i/, respectively. For female sounds, the max duration is 0.937 s in /\(\kappa\):/, and the min duration is 0.057 s in /i/. The average maximum and minimum durations are 0.470 s in /u:/ and 0.133 s in /i/, respectively. The pronunciation of /i/ for both males and females have a very short duration.  
Figure 1 shows the maximum, minimum, and average duration of male and female vowel sounds. The top three symbols represent the durations of the male sounds, and the lower three symbols represent the durations of the female sounds. The greatest duration of vowel sounds is found in females; the female duration is longer than the male in all vowels. The minimum duration in each vowel for males and females is approximately the same, but the average duration of all vowels in females is longer than males.  
Figure 2 shows the average durations of Thai vowels. The first nine bars on the x-axis are long vowels. and the last nine bars on the x-axis are short vowels. The y-axis represents the duration of Thai vowel sounds, ranging from 0.0 to 0.45 s. It can be seen that the long vowels' average duration of pronunciation is longer than that of the short vowels. The long vowels average is 0.3-0.4 s, whereas the short vowels average at 0.1-0.2 s. It is apparent that the vowels are different lengths.  
Based on an exploration of vowel wave files that have been examined by a linguist, certain features were identified. For instance, while speaking, the characteristics of each vowel sound are different because the pronunciation of each vowel varies in many aspects such as gender, style of speaking, loudness, duration, age, and environment. Vowel sound files should therefore be preprocessed to obtain the appropriate form of information for the next stage.  
Figure 1: Durations of Thai vowel sounds.