An acoustic comparison of the vowels and diphthongs of first and second language South African English

Speaker accent influences the accuracy of automatic speech recognition (ASR) systems. Knowledge of accent-based acoustic variations can therefore be used in the development of more robust systems. This paper investigates the differences between first language (L1) and second language (L2) English in South Africa and is specifically aimed at L2 English speakers with a native African mother tongue for instance Xhosa, Zulu or South Sotho. The vowel systems of English, and African languages, as described in the linguistic literature, were compared to predict the expected deviations of L2 South African English from the L1 norm. A total of fifty context dependent phonemes from L1 and L2 speakers were acoustically compared and analysed in both formant and mel-scaled cepstral domains. The measured variations compared favourably to those linguistically predicted. The long term goal of this project is to aid in the adaptation of existing L1 English recognition systems for South African L2 English.