Acoustics of the glottal source at closures for fricative and stop consonants

Previous research on acoustic distinctions between manner classes of obstruent consonants has primarily considered differences at the release. This study investigates acoustic distinctions in the glottal waveforms at the closure. It is hypothesized that the higher pressure generated in a complete closure (stops and affricates) results in a more rapid cessation of vibration of the glottis than for a partial closure (fricatives). This can be measured by rate of energy offset at the closure landmark. This work studies measurements of the rate of change of energy at closure in various frequency bands. For lower frequencies, in the range of the first formant or below, it is expected that there is interaction between voicing and manner due to the presence of a ‘‘voicebar’’ (continued vibration) during the closure. Preliminary measurements show that both voiced and voiceless stop consonants exhibit more rapid rates of energy offset than fricatives in a frequency band containing the second formant. This measure may be useful in noisy environments where the energy of frication is obscured; the periodic glottal waveform can be more reliably measured in noise, e.g., by autocorrelation-based methods. [Work supported by NIH Grant No. DC02978.]