The measurement of formant frequencies of vowels is among the most common measurements in speech studies, but measurements are known to be biased by the particular fundamental frequency (F0) exciting the formants. Approaches to reducing the errors were assessed in two experiments. In the first, synthetic vowels were constructed with five different first formant (F1) values and nine different F0 values; formant bandwidths, and higher formant frequencies, were constant. Input formant values were compared to manual measurements and automatic measures using the linear prediction coding-Burg algorithm, linear prediction closed-phase covariance, the weighted linear prediction-attenuated main excitation (WLP-AME) algorithm [Alku, Pohjalainen, Vainio, Laukkanen, and Story (2013). J. Acoust. Soc. Am. 134(2), 1295-1313], spectra smoothed cepstrally and by averaging repeated discrete Fourier transforms. Formants were also measured manually from pruned reassigned spectrograms (RSs) [Fulop (2011). Speech Spectrum Analysis (Springer, Berlin)]. All but WLP-AME and RS had large errors in the direction of the strongest harmonic; the smallest errors occur with WLP-AME and RS. In the second experiment, these methods were used on vowels in isolated words spoken by four speakers. Results for the natural speech show that F0 bias affects all automatic methods, including WLP-AME; only the formants measured manually from RS appeared to be accurate. In addition, RS coped better with weaker formants and glottal fry.
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We thank the participants who made manual measurements of the stimuli, and explained their methods; we thank the speakers of the natural speech corpus. Thanks to Mark Tiede for providing alternate analysis methods, to Sean Fulop for help with the reassigned spectrogram, and to Paavo Alku and Manu Airaksinen for help and their code for the WLP-AME method. Thanks to the four anonymous reviewers for their comments. This work was supported by National Institutes of Health-National Institute on Deafness and Other Communication Disorders (NIH-NIDCD) Grant No. DC-002717 to Haskins Laboratories. C.H.S. and H.N. contributed equally to this study.
© 2016 Acoustical Society of America.
ASJC Scopus subject areas
- Arts and Humanities (miscellaneous)
- Acoustics and Ultrasonics