Acoustic analysis of diphthongs in Standard South African English

Abstract

Diphthongs typically form an integral part of the phone sets used in English ASR systems. Because diphthongs can be represented using smaller units (that are already part of the vowel system) this representation may be inefficient. We evaluate the need for diphthongs in a Standard South African English (SSAE) ASR system by replacing them with selected variants and analysing the system results. We define a systematic process to identify and evaluate replacement options for diphthongs and find that removing all diphthongs completely does not have a significant detrimental effect on the performance of the ASR system, even though the size of the phone set is reduced significantly. These results provide linguistic insights into the pronunciation of diphthongs in SSAE and simplifies further analysis of the acoustic properties of an SSAE ASR system.