Fifty years of monophthong and diphthong shifts in Mainstream Australian English

In this chapter we report on a diachronic acoustic analysis of Mainstream Australian English (MAusE) monophthongs and diphthongs, produced by young female speakers from Sydney. We examined the first and second formant frequencies for 11 monophthongs extracted from read speech data from the 1960s, 1990s, and 2010s. Focusing on patterns of relationships between the monophthongs at each of three historical time points, we highlight possible chain and parallel shifts. This analysis revealed a set of changes suggesting anticlockwise rotation of the system of monophthongs, resulting in a reduction of the four-way height contrast observed in the 1960s to a three-way height system in the later time periods. We also examined four selected diphthongs using generalised additive mixed models (GAMMs) to compare characteristics of the first and second formant trajectories between the 1960s and 2010s datasets. For each of the diphthongs, there were significant nonlinear differences over the 50-year time span, illuminating aspects of vowel change that may remain hidden without explicit analysis of dynamicity. Overall, the results suggest a close connection between monophthongs and diphthongs during vowel change showing parallel shifts and highlighting the need for continued research into connections across vocalic subsystems.