摘要:

The widespread use of echocardiography has generated considerable interest in the ultrasonic properties of myocardial collagen. This study was designed to investigate the effect of collagen on the propagation of ultrasound by measuring the anisotropy of ultrasonic velocity through formalin fixed specimens of bovine Achilles tendon. Tendon was chosen for this study because it possesses a high content of collagen and a well‐defined unidirectional arrangement of fibers. Ultrasonic velocity data were acquired from nine samples of fixed tendon that were each insonified at multiple angles relative to the fibers in 2° increments for a full 360°. Analysis of the data revealed a substantial angular dependence of velocity qualitatively similar to that reported for formalin fixed specimens of normal human myocardium, but approximately 17 times larger in magnitude. Together with measured values of density, these results were used to compute the elastic stiffness coefficientsC11(corresponding to propagation perpendicular to the fibers) andC33(corresponding to propagation parallel to the fibers) of fixed tendon, yielding 3.08 and 4.51 GPa, respectively.

ISSN:0001-4966    

DOI:10.1121/1.410139

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

A model of the bat sensorimotor system is developed using acoustics, signal processing, and control theory to illustrate the fundamental issues in accomplishing prey capture with echolocation. This model indicates that successful nonpredictive tracking of an ideal prey can be accomplished with a very simple system. Circular apertures approximate the mouth and ears for deriving acoustic beam patterns, using the big brown batEptesicusfuscusas a model. Fundamental and overtone frequency components in the emissions allow two simultaneous acoustic beams to be defined. A pair of nonlinear, time‐variable, sampled‐data controllers alter the bat’s heading by applying yaw and pitch heading corrections. The yaw correction attempts to position the prey in the midsagittal plane by nulling the interaural intensity difference of the fundamental component. The pitch correction compares the intensities of the overtone and fundamental components and acts to null their difference. By initiating pitch correction when the overtone intensity first exceeds that of the fundamental, the ambiguity problem is solved and the prey is directed to the capture region. Simulations of passive prey capture indicate that the capture probability decreases as the prey speed increases. Both quick and sluggish prey are considered, with sluggish prey found to be caught with slightly better efficiency. The magnitude of the prey’s lateral motion just prior to capture is observed to be an important factor determining capture. The presence of a blind stage is considered, during which the interference of the emission with the echo is assumed to disrupt any sonar information. The presence of such a blind stage is found to have negligible effect on capture efficiency.

ISSN:0001-4966    

DOI:10.1121/1.410140

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

The vibrato rate for ten singers, all singing Schubert’s Ave Maria, was measured on sonograms. Commercially available CD records were used to insure that the vibrato originated in a real musical performance. It was found, that the vibrato rate typically increased at the end of each tone, +15% in average, while no typical structure could be found in the beginning of a tone. Disregarding the increase of vibrato rate toward tone endings, the mean rate across singers was 6.0 Hz. The average variation between maximum and minimum rate within an artist is about ±8% of the artist’s average.

ISSN:0001-4966    

DOI:10.1121/1.410141

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

The maximum bow force for Helmholtz oscillations, and the frequency shift as a function of bow force, have been measured for unstopped notes on a variety of violin strings. A bowing machine is briefly described on which data using bowing velocities at 5 and 10 cm/s were obtained. Computer simulations using the standard friction function model of the bowed string were also done. The combination of the measurements and the simulations allow an assessment of the probable validity of the friction curve model of the force between bow hair and string in bowed string motion.

ISSN:0001-4966    

DOI:10.1121/1.410142

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

A new method of solution to the equation of a perfectly flexible string, when struck at any point by hard or soft narrow hammers, is developed. The hard hammer is modeled as a point mass, and the soft hammer is modeled as a point mass backed by a linear or nonlinear spring and a dashpot, representing the compliance and dissipation of the felt. For each hammer the equation describing the string–hammer contact force during the periods of contact, and of recontacts, is derived explicitly. The Green’s function for a fixed‐fixed string is represented by an infinite series of Heaviside functions. The analysis is exact in the spatial domain thereby eliminating modal truncation error and capturing all discontinuities in the contact force. The method predicts the contact force and system response under impacts given any hammer to string mass ratio that experiences any number of multiple contacts during the hammer strike.

ISSN:0001-4966    

DOI:10.1121/1.410143

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

In this paper, a quantitative and parametric model is presented that incorporates the role of context‐dependent formant transitions in phonetic decoding of speech. The idea is to use the locus equations established from speech science to constrain the model parameters so that the number of parameters for the context‐dependent model reduces to the same order as that for the context‐independent model. In contrast to the knowledge‐based, largely qualitative approaches employing also the formant transition information, our approach allows the parameters of the phonetic classifier, including the locus‐equation slopes and intercepts, in conjunction with the hidden Markov model parameters, to be subject to mathematical optimization via an effective and efficient training procedure developed in this study. Detailed analysis of the results obtained from automatic training shows that the estimates of the locus‐equation slopes and intercepts are consistent with those manually derived and reported in the speech science literature. Further, the experimental results using a phonetic classifier trained on the TIMIT database demonstrate the effectiveness of our new model, measured by a 15% classification error rate reduction, in comparison with a conventional statistical phonetic classifier under identical training and testing conditions.

ISSN:0001-4966    

DOI:10.1121/1.410144

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

This paper describes a linear predictive (LP) speech synthesis procedure that resynthesizes speech using a 6th‐order polynomial waveform to model the glottal excitation. The coefficients of the polynomial model form a vector that represents the glottal excitation waveform for one pitch period. A glottal excitation code book with 32 entries for voiced excitation is designed and trained using two sentences spoken by different speakers. The purpose for using this approach is to demonstrate that quantization of the glottal excitation waveform does not significantly degrade the quality of speech synthesized with a glottal excitation linear predictive (GELP) synthesizer. This implementation of the LP synthesizer is patterned after both a pitch‐excited LP speech synthesizer and a code excited linear predictive (CELP) speech coder. In addition to the glottal excitation codebook, we use a stochastic codebook with 256 entries for unvoiced noise excitation. Analysis techniques are described for constructing both codebooks. The GELP synthesizer, which resynthesizes speech with high quality, provides the speech scientist a simple speech synthesis procedure that uses established analysis techniques, that is able to reproduce all speed sounds, and yet also has an excitation model waveform that is related to the derivative of the glottal flow and the integral of the residue. It is conjectured that the glottal excitation codebook approach could provide a mechanism for quantitatively comparing the differences in glottal excitation codebooks for male and female speakers and for speakers with vocal disorders and for speakers with different voice types such as breathy and vocal fry voices. Conceivably, one could also convert the voice of a speaker with one voice type, e.g., breathy, to the voice of a speaker with another voice type, e.g., vocal fry, by synthesizing speech using the vocal tract LP parameters for the speaker with the breathy voice excited by the glottal excitation codebook trained for vocal fry.

ISSN:0001-4966    

DOI:10.1121/1.411319

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

A speaker structures utterances very clearly by grouping words into phrases. This facilitates the listener’s recovery of the meaning of the utterance and the speaker’s intention. To this purpose, a speaker uses, among other things, suprasegmental cues, such as intonation, pauses and prefinal lengthening of speech sounds. The research described here is concerned with the relationship between the strength of prosodic boundaries in spoken utterances as perceived by untrained listeners (perceptual boundary strength, PBS) and the phonetic cues melodic discontinuity, pause, declination reset and, to a limited extent, prefinal lengthening. The results indicate that untrained listeners can give reliable and usable judgments of PBS and that this is true even if the lexical contents of the utterances is made unrecognizable, thus blocking access to lexical, syntactic, and semantic information. There is a clear relation between PBS and the phonetic cues, the general trend being for PBS values to increase as more phonetic cues are associated with a given word boundary. The experimentally obtained PBS values were also compared with boundaries predicted on the basis of a syntactic and metrical analysis of the material. A high agreement was found between the PBS values found and the theoretically predicted prosodic structure.

ISSN:0001-4966    

DOI:10.1121/1.410145

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Temporal auditory analysis of acoustic events in various frequency channels is influenced by the ability to detect amplitude modulations which for normal hearing involves low‐pass filtering with a cutoff frequency around 100 Hz and a rejection slope of about 10 dB per decade. These characteristics were established in previous studies measuring modulation transfer functions. For cochlear implant subjects, the delivery of detailed amplitude modulation information has been recently shown to result in very significant improvements in speech understanding. Several previous studies on cochlear implant subjects have reported capacities for temporal resolution rather equivalent to those of normally hearing subjects but with some notable individual differences. Recently two studies on some cochlear implant subjects indicated modulation transfer functions often quite similar to those of normal hearing but exhibiting marked individual differences in shape and absolute sensitivity. The present study compared amplitude modulation detection and phonetic recognition in a group of cochlear implant subjects to determine the extent to which the two tasks are correlated. Nine individuals who had been implanted with an Ineraid device and who demonstrated open speech understanding ranging from excellent to poor were chosen and tested in the present study. For each subject modulation transfer functions were measured at the most apical electrode and phonetic recognition of isolated vowels and intervocalic consonants was assessed. Results showed a strong correlation between the depth of high‐frequency rejection in modulation transfer functions and success in vowel and consonant intelligibility. These results emphasize the importance of temporal speech features and offer perspectives for customizing signal processing in cochlear implants.

ISSN:0001-4966    

DOI:10.1121/1.410146

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

The intelligibility of speech stimuli recorded within the uterus of a pregnant sheep was determined perceptually using a group of untrained judges. The intrauterine sound environment of the ewe was intended to simulate that of a pregnant woman. Two separate lists, one of meaningful and one of nonmeaningful speech stimuli, were delivered through a loudspeaker to the side of the ewe and were simultaneously recorded with an air microphone located 15 cm from the flank and with a hydrophone previously sutured to the neck of the fetus. Perceptual test tapes generated from these recordings were played to 102 judges. The intelligibility of the phonemes recorded in the air was significantly greater than the intelligibility of phonemes recorded from the uterus. A male talker’s voice was more intelligible than a female talker’s voice when recorded from within the uterus, but not so when recorded in the air. An analysis of the feature information transmission from recordings inside and outside the uterus revealed that voicing information is better transmittedinuterothan place or manner information.

ISSN:0001-4966    

DOI:10.1121/1.410147

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP