Excitation of vocal-tract synthesizers

Relation of perceived breathiness to laryngeal kinematics and acoustic measures based on computational modeling

PURPOSE

In this study, the authors sought to determine (a) how specific vocal fold structural and vibratory features relate to breathy voice quality and (b) the relation of perceived breathiness to 4 acoustic correlates of breathiness.

METHOD

A computational, kinematic model of the vocal fold medial surfaces was used to specify features of vocal fold structure and vibration in a manner consistent with breathy voice. Four model parameters were altered: vocal process separation, surface bulging, vibratory nodal point, and epilaryngeal constriction. Twelve naïve listeners rated breathiness of 364 samples relative to a reference. The degree of breathiness was then compared to (a) the underlying kinematic profile and (b) 4 acoustic measures: cepstral peak prominence (CPP), harmonics-to-noise ratio, and two measures of spectral slope.

RESULTS

Vocal process separation alone accounted for 61.4% of the variance in perceptual rating. Adding nodal point ratio and bulging to the equation increased the explained variance to 88.7%. The acoustic measure CPP accounted for 86.7% of the variance in perceived breathiness, and explained variance increased to 92.6% with the addition of one spectral slope measure.

CONCLUSION

Breathiness ratings were best explained kinematically by the degree of vocal process separation and acoustically by CPP.

Phrase-level speech simulation with an airway modulation model of speech production

Artificial talkers and speech synthesis systems have long been used as a means of understanding both speech production and speech perception. The development of an airway modulation model is described that simulates the time-varying changes of the glottis and vocal tract, as well as acoustic wave propagation, during speech production. The result is a type of artificial talker that can be used to study various aspects of how sound is generated by humans and how that sound is perceived by a listener. The primary components of the model are introduced and simulation of words and phrases are demonstrated.

Source-tract interaction with prescribed vocal fold motion

An equation describing the time-evolution of glottal volume velocity with specified vocal fold motion is derived when the sub- and supra-glottal vocal tracts are present. The derivation of this Fant equation employs a property explicated in Howe and McGowan [(2011) J. Fluid Mech. 672, 428-450] that the Fant equation is the adjoint to the equation characterizing the matching conditions of sub- and supra-glottal Green's functions segments with the glottal segment. The present aeroacoustic development shows that measurable quantities such as input impedances at the glottis, provide the coefficients for the Fant equation when source-tract interaction is included in the development. Explicit expressions for the Green's function are not required. With the poles and zeros of the input impedance functions specified, the Fant equation can be solved. After the general derivation of the Fant equation, the specific cases where plane wave acoustic propagation is described either by a Sturm-Liouville problem or concatenated cylindrical tubes is considered. Simulations show the expected skewing of the glottal volume velocity pulses depending on whether the fundamental frequency is below or above a sub- or supra-glottal formant. More complex glottal wave forms result when both the first supra-glottal fundamental frequencies are high and close to the first sub-glottal formant.

Palatalization and intrinsic prosodic vowel features in Russian

The presented study is aimed at investigating the interaction of palatalization and intrinsic prosodic features of the vowel in CVC (consonant+vowel+consonant) syllables in Russian. The universal nature of intrinsic prosodic vowel features was confirmed with the data from the Russian language. It was found that palatalization of the consonants affects intrinsic fundamental frequency (IFO), intensity (I), and duration of the vowels in CVC syllables by modifying the vowel articulatory parameters such as vowel height and fronting. The obtained results are discussed in the light of opposing theories: those suggesting automatic control and those suggesting active control over intrinsic vowel features.

Relation of structural and vibratory kinematics of the vocal folds to two acoustic measures of breathy voice based on computational modeling

PURPOSE

To relate vocal fold structure and kinematics to 2 acoustic measures: cepstral peak prominence (CPP) and the amplitude of the first harmonic relative to the second (H1-H2).

METHOD

The authors used a computational, kinematic model of the medial surfaces of the vocal folds to specify features of vocal fold structure and vibration in a manner consistent with breathy voice. Four model parameters were altered: degree of vocal fold adduction, surface bulging, vibratory nodal point, and supraglottal constriction. CPP and H1-H2 were measured from simulated glottal area, glottal flow, and acoustic waveforms and were related to the underlying vocal fold kinematics.

RESULTS

CPP decreased with increased separation of the vocal processes, whereas the nodal point location had little effect. H1-H2 increased as a function of separation of the vocal processes in the range of 1.0 mm to 1.5 mm and decreased with separation > 1.5 mm.

CONCLUSIONS

CPP is generally a function of vocal process separation. H1*-H2* (see paragraph 6 of article text for an explanation of the asterisks) will increase or decrease with vocal process separation on the basis of vocal fold shape, pivot point for the rotational mode, and supraglottal vocal tract shape, limiting its utility as an indicator of breathy voice. Future work will relate the perception of breathiness to vocal fold kinematics and acoustic measures.

Amplitude modulation of turbulence noise by voicing in fricatives

The two principal sources of sound in speech, voicing and frication, occur simultaneously in voiced fricatives as well as at the vowel-fricative boundary in phonologically voiceless fricatives. Instead of simply overlapping, the two sources interact. This paper is an acoustic study of one such interaction effect: the amplitude modulation of the frication component when voicing is present. Corpora of sustained and fluent-speech English fricatives were recorded and analyzed using a signal-processing technique designed to extract estimates of modulation depth. Results reveal a pattern, consistent across speaking style, speaker, and place of articulation, for modulation at fo to rise at low voicing strengths and subsequently saturate. Voicing strength needed to produce saturation varied 60-66 dB across subjects and experimental conditions. Modulation depths at saturation varied little across speakers but significantly for place of articulation (with [z] showing particularly strong modulation) clustering at approximately 0.4-0.5 (a 40%-50% fluctuation above and below unmodulated amplitude); spectral analysis of modulating signals revealed weak but detectable modulation at the second and third harmonics (i.e., 2fo and 3fo).

Aeroacoustic production of low-frequency unvoiced speech sounds

A theoretical approach to describing unvoiced speech sound production is outlined using the essentials of aerodynamics and aeroacoustics. The focus is on the character and role of nonacoustic air motion in the vocal tract. An idealized picture of speech sound production is presented showing that speech sound production involves the dynamics of a jet flow, characterized by vorticity. A formal expression is developed for the sound production by unsteady airflow in terms of jet vorticity and vocal-tract shape, and a scaling law for the aeroacoustic source power is derived. The generic features of internal jet flows such as those exhibited in speech sound production are discussed, particularly in terms of the vorticity field, and the relevant scales of motion are identified. An approximate description of a jet as a train of vortex rings, useful for sound-field prediction, is described using the scales both of motion and of vocal-tract geometry. It is shown that the aeroacoustic source may be expressed as the convolution of (1) the acoustic source time series due to a single vortex ring with (2) a function describing the arrival of vortex rings in the source region. It is shown that, in general, the characteristics of the aeroacoustic source are determined not only by the strength, spatial distribution, and convection speed of the jet vorticity field, but also the shape of the vocal tract through which the jet flow passes. For turbulent jets, such as those which occur in unvoiced sound production, however, vocal-tract shape is the dominant factor in determining the spectral content of the source.

Frication noise modulated by voicing, as revealed by pitch-scaled decomposition

A decomposition algorithm that uses a pitch-scaled harmonic filter was evaluated using synthetic signals and applied to mixed-source speech, spoken by three subjects, to separate the voiced and unvoiced parts. Pulsing of the noise component was observed in voiced frication, which was analyzed by complex demodulation of the signal envelope. The timing of the pulsation, represented by the phase of the anharmonic modulation coefficient, showed a step change during a vowel-fricative transition corresponding to the change in location of the noise source within the vocal tract. Analysis of fricatives [see text] demonstrated a relationship between steady-state phase and place, and f0 glides confirmed that the main cause was a place-dependent delay.