Investigating the effect of F0 and vocal intensity on harmonic magnitudes: data from high-speed laryngeal videoendoscopy

The relative magnitude of the first two harmonics of the voice source (H1*-H2*) is an important measure and is assumed to be one exponent of changes in vocal quality along a breathyto-pressed continuum. H1*-H2* is often associated with glottal open quotient (OQ) and glottal pulse skewness (as quantified by speed quotient, SQ), but may also covary with fundamental frequency (F0) and vocal intensity. We examined the relationship between H1*-H2*, F0, and vocal intensity using phonations in which vocal qualities varied continuously in F0 and intensity. Glottal area measures (OQ and SQ) and acoustic measures (F0, intensity, and H1*-H2*) were studied using simultaneously-collected laryngeal high-speed videoendoscopy and audio recordings from 9 subjects. Analyses of individual speakers showed that H1*-H2* may sometimes vary as a function of F0 alone, with OQ and SQ remaining rather constant, hypothetically when nonlinear source-filter interaction is strong. Although conventionally H1*-H2* is assumed to decrease with increasing vocal intensity due to a decrease in OQ, results showed examples where H1*-H2* increased with increasing vocal intensity, hypothetically when the effect of decreasing pulse skewness exceeds the effect of decreasing OQ. In some phonatory modes, the relationship between SQ and H1*H2* may not be as monotonic as previously assumed.