Characterization of Amharic Vowel Sound Units

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Addis Ababa University


Vowel sound unit characterization is a process of studying the acoustic characteristics or behaviors of vowel speech units within different contexts. It is used to describe the phonetic and acoustic features of the respective speech units and avoid inappropriate parameter selection in concatenative and formant based Text to Speech (TTS) systems. This study focused on the acoustic characteristics of Amharic vowel sound units. The characteristics of vowels are studied in Consonant-Vowel-Consonant (CVC) contexts using formant and duration based characterization approaches. In the study, context specification and text corpus preparation was done and listening test was conducted on the recorded speech signals. Then the speech signal is labeled to extract the vowel segment features such as first formant frequency (F1), second formant frequency (F2), third formant frequency (F3), fundamental frequency (F0) and duration. Finally, aggregate feature extractors were conducted on the sample vowel features in order to acquire the acoustic characteristics of the vowel sound units. At run time, the effect of speaking rate on duration, the influence of duration on formant frequency values and formant frequency variability occurred due to loudness/ intensity and adjacent contexts were described. The characterization shows that the duration of vowels is affected by the speaking rates. This implies that vowel duration is short within contexts that are recorded at fast speaking rate while the vowel duration is long within contexts that are recorded at normal speaking rate. Similarly, the formant frequency values of vowels are affected by the duration. So, F1 is inversely proportional to duration while F2 and F3 are directly proportional to duration. The characterization was evaluated by visualizing acoustic vowel space and through comparing and contrasting with International Phonetic Alphabet (IPA) maps of vowels. The evaluation shows that acoustic vowel space is dependent on duration, context and loudness/ intensity. However, these factors have not a big influence on the acoustic space rather they make a little shift of vowel position on the space. Keywords: Vowel, Vowel Characterization, Formant, Acoustic vowel space, Articulatory vowel space



Vowel, Vowel Characterization, Formant, Acoustic Vowel Space, Articulatory Vowel Space