Variation in spectral slope and interharmonic noise in Cantonese tones

To provide reference data for studies of voice quality variation in lexical tone, an experiment is described to investigate the nature of intrinsic variation in spectral slope and interharmonic noise for Cantonese citation tones. 23 spectral slope and interharmonic noise measures are extracted with VoiceSauce from the tones on /o/ Rhymes of five male and five female speakers of conservative Cantonese. Significant correlation between F0 and both spectral slope and interharmonic noise is demonstrated. It is shown with probabilistic bivariate discriminant analysis that even tones with no extrinsic voice quality differences can be identified at rates considerably above chance from a combination of their spectral slope and interharmonic noise. Male tones, with a minimal error rate of 5.7%, are identified twice as well as female, with a minimal error rate of 14.5%. Combinations with uncorrected spectral slopes perform better than corrected. The best combinations for both sexes involve slope parameters H2H4 (difference between the 4^th and 2^nd harmonic amplitudes); and H42K (difference between the 4^th harmonic and nearest harmonic to 2 kHz), irrespective of noise parameters. The worst combinations involve CPP (cepstral peak prominence) as a noise parameter.