Computational Methods for Normalizing Acoustic Vowel Data for Talker Differences

Direct acoustic- phonetic comparison of vowels produced by different talkers can be difficult due to the effects of anatomical and physiological talker differences on first and second formant frequencies. Since the mid-1960s, numerous computational algorithms have been proposed to normalize formant frequency measures and reduce the effects of talker-specific variability. These algorithms vary widely in their conceptualization: some require samples of the entire vowel space (vowel extrinsic), whereas others can be conducted on a single vowel class (vowel intrinsic); some are based on a single-scale factor to align broad classes of talkers (such as females and males), whereas others use scale factors and/or vowel space ranges for individual talkers to align their vowel systems in the same acoustic- phonetic space. In this study, an overview of the most commonly used normalization algorithms is provided and the advantages and disadvantages of each of the approaches are discussed.