摘要:

Bats use the rich food resources of the night by specializing in audition. They emit short echolocation sounds and listen to the echoes returning from potential prey. The bat’s auditory system analyzes spectral and temporal parameters of echoes for detecting, locating, and identifying a target. Different bat species have solved the problem of acoustic target detection and pattern recognition even in clustered situations by focusing on certain acoustical features of a target. The specialized motion detection by horseshoe bats, for instance, analyzes small echofrequency shifts modulated onto a long constant frequency echolocation signal. These frequency modulations are Doppler shifts within echoes returning from wing beating insects. For detecting modulations as small as 10 Hz or 0.01%, horseshoe bats have in the cochlea an extremely narrow filter (Q?500) matched to the carrier frequency (i.e., echolocation sound) of 83 kHz. The filter is realized by structural differentiations of the basilar membrane and the filter frequencies are represented on the basilar membrane in an expanded fashion. We have called this specialized patch of the basilar membrane an ’’acoustical fovea.’’ The ’’foveal frequencies’’ are largely overrepresented in the tonopical arrangement of the ascending auditory pathway. The bats have developed a feedback system which lowers the emitted frequency during flight in such a way that the Doppler shifted echofrequency is kept precisely at a fixed reference frequency of the fovea. This feedback system and other neuronal data disclose an intricate coupling of the auditory and vocalizing system. The evolution of echolocation in bats has driven the analyzing capacities of audition in both frequency and time domain close to theoretical limits. Investigations of such specialized systems give fascinating insights into capacities and possible general principles of auditory information processing.

ISSN:0001-4966    

DOI:10.1121/1.384812

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The design of Tonpilz piezoelectric transducers often involves the satisfaction of multiple, conflicting design specifications. To arrive at an optimal compromise solution to a specific design formulation, nonlinear goal programming techniques can be applied. For this optimization technique, a mathematical model of the transducer and its associated housing is constructed and the values of the desired transducer responses and attributes—the design objectives—are computed. The nonlinear goal programming formulation minimizes the differences between the objectives and their specifications. The use of priorities and weights in this minimization process is the key to the great utility of the technique. An example of the application of nonlinear goal programming in a simple hypothetical transducer design is presented to demonstrate the value of the optimal compromise approach for this or more complex systems.

ISSN:0001-4966    

DOI:10.1121/1.384813

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The frequency response of sound pressure and top plate mobility is studied around the two first resonances of the guitar. These resonances are shown to result from a coupling between the fundamental top plate mode and the Helmholtz resonance of the cavity. A simple model is proposed for low‐ frequency guitar function. The model predicts frequency responce of sound pressure and top plate mobility which are in close quantitative agreement with experimental responses. The absolute sound pressure level and mobility level are predicted to within a few decibels, and the equivalent piston area of the top plate is determined. All parameters of this model can directly be derived from measurements of the frequencies of the two first resonances and of the cavity Helmholtz resonance. The Helmholtz resonance is found as the antiresonance in the spectrum of top plate mobility.

ISSN:0001-4966    

DOI:10.1121/1.384814

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A simplified treatment is given of the mechanism of sound production in musical instruments driven by air jets, which is sufficiently explicit that semiquantitative predictions can be made about the effects of certain variables upon the harmonic structure of the sound produced. In particular it is found that the amplitude of the even harmonics, generally, and of the second harmonic, particularly, is quite critically dependent upon the offset of the pipe lip from the symmetry plane of the jet. A completely symmetrical relationship (zero offset) reduces the generated amplitude of the second harmonic by a large factor. Experimental results with an adjustable organ pipe are found to confirm these predictions. The implications of these results for the voicing of organ pipes and recorders and for subtle tonal variation in flute playing are briefly discussed.

ISSN:0001-4966    

DOI:10.1121/1.384815

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The timing of the last tones constituting the final retard is studied in performances of motor music, i.e., music dominated by long sequences of short and equal note values frequently accompanied by similar series of twice as long note values. The results suggest that the retard length is related to the length of the final cadence and that the retards are divided into two phases, the first of which is variable while the second is more regular; its length and decrease in tempo depends on the length of the last conceptual unit (motive) of the piece and, as regards the decrease in tempo, also the preretard mean tempo, with which the piece is played. The same preretard mean tempo also determines the duration of the note preceding the final chord. These observations are expressed in a set of equations by means of which retards are computed for a set of compositions. The musical quality of such rule generated retards is assessed by a jury of experienced musicians and music listeners.

ISSN:0001-4966    

DOI:10.1121/1.384816

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A traditional model of the speech signal has provided the underpinning of vocoder technology since the inception of analysis/synthesis telephony. The model is a first‐order approximation to human speech generation in which the source of vocal sound and the resonant acoustic system are treated as linear, separable elements. This source‐system model cannot properly account for a number of acoustic factors now known to exist in speech generation. We propose and implement here a signal model based more directly upon the phsyics of of speech generation. We also implement parametric control of the synthesis model by an adaptive procedure that minimizes the spectral difference between a human speech input and the synthetic output of the model.The adapted parameters constitute a low bit‐rate representation of the input human speech. We test a preliminary form of the system by computer simulation and demonstrate that in simple inital trials the signal model is able to adapt in a realistic manner.

ISSN:0001-4966    

DOI:10.1121/1.384817

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Laryngeal articulatory movements and their coordination with supralaryngeal events have proved to be important for control of voicing and pre‐ and post‐aspiration in obstruents. A reciprocal pattern of activity generally has been observed among laryngeal abductor and adductor muscles in the control of glottal opening in voiceless obstruent production. Current notions about laryngeal articulatory control rest, however, mainly on studies using simple linguistic materials, where voiced and unvoiced segments alternate in a regular manner. The present study examines laryngeal activity in voiceless obstruent clusters using the combined techniques of electromyography, fiberoptic filming, and transillumination of the larynx. The results indicate that laryngeal articulatory movements are precisely coordinated with the oral articulations of clusters to meet the aerodynamic requirements of speech production. Several laryngeal movements may occur in a cluster. Comparison of temporal patterns of glottal area variations obtained by fiberoptic filming and by transillumination of the larynx, showed them to be practically identical.

ISSN:0001-4966    

DOI:10.1121/1.384774

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Five monaural chinchillas were trained with a method of shock‐avoidance conditioning to respond to silent intervals, or gaps, in an otherwise continuous noise. The noise was low‐pass filtered at either 10 or 6 kHz and presented at six intensities ranging between 23‐ and 77‐ dB sound‐pressure level (SPL). Gap detection thresholds were determined according to the method of constant stimuli. For both noise bands, gap thresholds were approximately 3 ms at the highest intensity levels and increased to approximately 6 ms at the lowest level. The results obtained from the chinchilla are in general agreement with those obtained from man.

ISSN:0001-4966    

DOI:10.1121/1.384818

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

According to a recent extension of our theory of intensity perception [Limetal., J. Acoust. Soc. Am. 62, 1256–1267 (1977)], two stimuli are matched in loudness if and only if their intensities divide the respective dynamic ranges proportionally in terms of just noticeable differences. This study reports results of intensity discrimination and loudness matching experiments designed to test this prediction. Data were obtained over most of the dynamic range for three different types of sounds: a 1000‐Hz tone in quiet, a 1000‐Hz tone partially masked by a 2‐octave band of noise, and spectrally flat wide‐band noise. Of the five subjects tested, three produced results that had sufficient internal consistency to be useful for testing the predictions. For these subjects, the data and the theory were found to be reasonably consistent. Comparison with other studies, however, reveals that loudness matching results vary with matching paradigm by an amount that is significant with respect to the task of evaluating the theory. Hence, a rigorous test of the theory requires an improved understanding of the effects of matching paradigm.

ISSN:0001-4966    

DOI:10.1121/1.384819

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

These experiments are concerned with the frequency distribution of two‐tone suppression in forward masking. In each experiment the threshold of a 20‐msec probe tone following a 300‐msec masker was determined as a function of probe frequency. In experiments I and II this was done for two maskers (a single tone with frequencyfm, and that tone with a suppressing tone added) which had previously been equated for their masking effectiveness atfmby adjusting the levels of the components atfm. The maskers were equally effective only in a restricted frequency region aroundfm, a result which is not consistent with the idea that suppression is equivalent to a simple reduction in level of the suppressed tone. In experiment III probe thresholds were measured for a fixed tone at 2 kHz with and without a suppressing tone whose frequency was systematically varied. The suppression, measured as the reduction in probe threshold produced by adding the suppressing tone, was found to have two components. One of these was limited to a narrow range of probe frequencies around 2 kHz and is attributed to a qualitative change in the cues available to the observer when a suppressing tone is added to the masker. The other component shifted in frequency as the suppressor frequency was altered and is explained as a reduction in level of only part of the excitation pattern of the suppressed tone.

ISSN:0001-4966    

DOI:10.1121/1.384820

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP