Measurement of formants in synthetic vowels

Abstract

The measurement of formant frequencies of vowels is among the most common measurements in speech studies, but is known to be biased by the particular fundamental frequency (F0) exciting the formants, and to be inaccurate for formants close together or for speakers using a high F0. To allow a comparison across multiple measurement techniques, vowels were synthesized using the Klatt synthesizer with known formant values. The synthetic vowels were constructed with five different F1 values and nine different F0 values; formant bandwidths, and higher formant frequencies, were constant. The F0s varied in such a way that the most intense harmonic in F1 or F2 either matched the center frequency or deviated in the range of 3–87 Hz. Manual measurements by four subjects were compared to automatic measures using the LPC Burg algorithm, LP closed-phase covariance, and spectra smoothed cepstrally or by averaging repeated DFT's. Formants were also measured from pruned reassigned spectrograms. Error patterns differ among the methods, but most tracked the frequency of the most intense harmonic; the smallest errors occur with closed-phase covariance and reassigned spectrogram. Implications for such measures on vowels in isolated words of real speech are discussed. [Work supported by NIH-NIDCD grant DC-002717.]