Huiqun Deng

A New Method for Obtaining Accurate Estimates of Vocal-Tract Filters and Glottal Waves From Vowel Sounds

Previously, estimating vocal-tract filters and glottal waves from vowel sounds imposed either the invalid assumption that glottal waves over closed glottal intervals are zero, or parametric models for glottal waves, resulting in biased vocal-tract-filter estimates and glottal-wave estimates lacking information over closed glottal intervals. We obtain unbiased vocal-tract-filter estimates from sustained vowel sounds, for which the glottal waveforms are periodically stationary random processes. Two equations are constructed each relating the vocal-tract filter to the sound signal and the glottal wave over one of two closed glottal intervals. By subtracting one equation from the other, the periodic components of the glottal wave are eliminated from the vocal-tract-filter estimation, and an unbiased vocal-tract-filter estimate is obtained. The average of many such estimates from different closed glottal intervals of the sound is the final estimate, which is used to obtain the glottal wave by inverse filtering the sound. The results obtained from vowel sounds /a/ produced by some subjects are presented. Over closed glottal phases, the glottal waves obtained are nonzero. During vocal-fold colliding, they increase; during vocal-fold parting, they decrease or even increase. The vocal-tract filters obtained yield vocal-tract area functions similar to that measured from an unknown subjects magnetic resonance image.

Obtaining LIP and Glottal Reflection Coefficients from Vowel Sounds

Knowledge about lip and glottal reflection coefficients during phonation is needed to eliminate their distortion effects on the estimates of vocal-tract area functions and glottal waves from vowel sounds. Direct measurements of these coefficients at human mouths are difficult. This paper presents a method for estimating them from vowel sounds. The estimation encounters an ill-defined inverse problem: the number of unknowns is greater than the number of constraints, and non-unique solutions exist for a sound. To overcome this problem, this paper uses a vowel sound produced by a subject whose vocal-tract area function (VTAF) for the sound is known. The estimates of the lip and the glottal reflection coefficients are determined as those that lead to a VTAF solution most similar to the known VTAF for the sound. The lip and the glottal reflection coefficients obtained for /a/ and /i/ are presented

Estimating the glottal waveform and the vocal-tract filter from a vowel sound signal

A pitch-synchronous signal processing method for estimating the glottal waveform and the vocal-tract filter is presented. This method is advantageous over existing methods. First, no assumptions about the shape of the glottal wave are made in the estimation, and consequently it can be used for any types of voices. Second, it can obtain more detailed structures of the derivative of the glottal wave than using other methods. Third, the influence of the glottal wave on the estimation of the vocal-tract filter is eliminated. The glottal waveform, the derivative of the glottal wave and the vocal-tract filter obtained using this method for two vowel sounds, produced by a female and a male subject, are illustrated. This method has applications in speech pathology, speech synthesis, speaker identification and so on.

Effects of glottal and lip boundary conditions on vocal-tract area function estimates from speech signals

High-resolution vocal-tract area functions (VTAF) can be derived from vocal-tract filters (VTF) estimated from vowel sound signals with a wide bandwidth. However, the effects of open glottises and frequency-dependent lip reflection coefficients contained in the VTF estimates distort the VTAF estimates. Given VTF estimates obtained over closed glottal phases, we provide a method for eliminating the distortion effects of frequency-dependent lip reflection coefficients on the VTAF estimates. When the VTF estimates contain limited effects of incomplete glottal closures, this method can still obtain reasonable VTAF estimates if the vowel sounds are produced with large lip openings. The VTAF estimates obtained using our method from sounds /a/ produced by different subjects are very similar to that measured using the magnetic resonate imaging method. Theoretically, to eliminate both distortions caused by lip reflection coefficients and incomplete glottal closures in the VTAF estimates, lip-opening areas must be known.

Estimating vocal-tract area functions from vowel sound signals over closed glottal phases

Existing methods that estimate the vocal-tract area functions (VTAF) from vocal-tract filters (VTF) using speech signals suffer from inadequate elimination of the glottal wave, and the influence of non-ideal vocal-tract boundary conditions. To minimize these effects on the VTF estimation, we present a method that jointly estimates the glottal wave and the VTF corresponding to closed glottal phases. Experimental results show that our method yields better estimates. The VTAF obtained for /a/ and /i/ each produced by a female and a male subject show that more detailed and accurate VTAF are obtained using the speech signals corresponding to closed glottal phases.

Glottal Waves via Inverse Filtering of Vowel Sounds

This paper shows how to obtain accurate glottal waves via inverse filtering of vowel sounds and how to determine if these glottal waves contain any significant resonance of vocal tracts. We obtain vocal-tract filter (VTF) estimates for the inverse filtering from sustained vowel sounds over closed glottal phases using a new method, which minimizes the effects of glottal waves on the VTF estimates. It is common that VTF estimates contain the effects of incomplete glottal closures, and the glottal waves obtained via inverse filtering contain residual vocal-tract resonance. Our simulations show that the residual resonance appears as stationary ripples superimposed on the derivatives of the original glottal waves over the duration of a glottal cycle. The VTF estimates and the glottal waves obtained from sustained vowel sounds /a/ produced by male and female subjects are presented. The derivatives of the obtained glottal waves exhibit transient positive peaks during vocal-fold collision and negative levels in the earlier stage of vocal-fold parting

Glottal‐wave and vocal‐tract‐area‐function estimations from vowel sounds based on realistic assumptions and models

Estimating glottal waves by inverse filtering vowel sounds and deriving vocal‐tract area functions (VTAFs) from vocal‐tract filter (VTF) estimates require that VTF models be realistic and that VTF estimates contain no effects of open glottises and glottal waves. In this study, VTFs are modeled to have lip reflection coefficients with low‐pass frequency responses; to minimize the effects of open glottises and glottal waves on the estimates, VTFs are estimated from sustained vowel sounds over closed glottal phases, assuming that the glottal waves are periodically stationary random processes. Since incomplete glottal closures are common, VTF estimates may contain the effects of glottal loss. To eliminate the effects of glottal loss in the VTF estimates, lip‐opening areas must be known. Theoretically, estimates of glottal waves and VTAFs corresponding to large‐lip‐opening vowel sounds are less affected by the glottal loss than those corresponding to small‐lip‐opening vowel sounds. The VTAFs and glottal waves estimated from vowel sounds produced by several subjects are presented. The normalized VTAFs estimated from large‐lip‐opening sounds are similar to that measured from an unknown subjects magnetic resonance image. Over closed glottal phases, the glottal waves are non‐zero. They increase during vocal‐fold colliding, and decrease or even increase during vocal‐fold parting.