Determining spectral stability in vowels: A comparison and assessment of different metrics

This study investigated the performance of several metrics used to evaluate spectral stability in vowels. Four metrics suggested in the literature and a newly developed one were tested and compared to the traditional method of associating the spectrally stable portion with the middle of the vowel. First, synthetic stimuli whose spectrally stable portion had been defined in advance were used to evaluate the potential of the different metrics to capture spectral stability. Second, the output of the different metrics on the acoustic measurements obtained in the vowel portions identified as spectrally stable was compared on both synthesized and natural speech. It is clear that higher-dimensional features are needed to capture spectral stability and that the best-performing metrics yield acoustic measurements that are similar to those obtained in the middle of the vowel. This study empirically validates long-standing intuitions about the validity of selecting the middle section of vowels as the preferred method to identify the spectrally stable region in vowels.