Principal component analysis of the interaction between spectral band power and pitch in classical singing voices

This study explores how the spectral information of vowel production targets changes by pitch in classical singing. Although it is established that singers engage in pitch-dependent vocal tract adjustments, less is known about how spectral envelope contrasts between vowel targets change by pitch and how consistent the patterns are across singers. Seven professional classical singers sang seven vowels across their pitch range. The energy of 16 spectral bands at every 500 Hz interval up to 8000 Hz was measured. Principal component analyses were performed to describe spectral variation. Results show consistent changes in spectral energy distribution as pitch increases despite individual differences in pitch range. A separate set of analyses further uses the center of gravity, standard deviation, skewness, and kurtosis of the spectra as a proxy for spectral shape variation, showing that the summarized spectral envelopes of vowel production targets systematically converge at higher pitches. Overall results suggest that pitch-dependent vocal tract adjustments may be shaped not only by singers' acoustic targets, but also by physiological constraints relative to each singer's overall pitch range. More broadly, this study demonstrates the possibility of using dimensionality reduction methods to characterize spectral patterns in high-pitched singing when formant tracking fails.