摘要:

The signal processing gain by digital beamforming in Doppler sonar was investigated in terms of the enhancement of signal‐to‐reverberation ratio (SRR) at the postbeamforming Doppler‐filter output with an objective to determine the minimum number of bits necessary for the quantization of beamformer channel input signals without appreciable degradation of sonar performance. The formulation of the problem follows closely the author’s earlier work which extends Davenport’s analysis of bandpass limiter to the more general multichannel multibit signal processors. Owing to the Doppler shift of target signal frequency and the relatively narrow bandwidth of Doppler filters, we express the frequency selective effect in the nonlinear interacting power series in terms of a new set of coefficientscmk, which bear crucial significance in sonar performance. Extensive numerical calculations of ’’Doppler processing gain’’ were carried out to demonstrate that four‐bit quantization of array transducer signals is theoretically sufficient to yield a performance essentially identical to that of a linear beamformer, but severe loss of gain could result if fewer than four bits are taken at the quantizer output. It is further demonstrated numerically and substantiated analytically that, for small input SRR, the processing gain of a digital beamformer with Doppler filters cannot exceed that of a linear (or optimized four‐bit digital) beamformer even it its channel signals are quantized into more than four bits.

ISSN:0001-4966    

DOI:10.1121/1.381367

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The crossed olivocochlear bundle (COCB) was stimulated with biphasic pulse trains while recording the cochlear summating potential (SP) with electrodes placed in scala vestibuli and tympani of either the first, second, or third cochlear turns of 21 guinea pigs. The outputs of the two electrodes were subsequently added (AVE SP) and subtracted (DIF SP) so that various components of the SP could be analyzed. It is shown that the DIF SP was consistently altered in a positive direction in all three cochlear turns at all frequencies and intensities during efferent activation. The greatest relative COCB effect for the DIF SP was achieved when it was recorded at low intensities and from the second and third turns of the cochlea. Both AVE SP components were significantly decreased in magnitude when recorded from the first turn during COCB stimulation. Data collected from turns two and three suggested that the efferent system exerts a strong positive influence on the overall AVE SP response. The results suggest that the efferent influences on the SP are consistent with models of COCB action on hair cells. Further, the findings conform to what would be predicted by other biasing techniques, and therefore it is recommended that COCB stimulation be considered as a tool for studying the origin and function of the cochlear potentials.

ISSN:0001-4966    

DOI:10.1121/1.381368

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Several aspects of two‐tone suppression in auditory‐nerve fibers have been reproduced in a nonlinear computational model for motion of the basilar membrane. In the model, a distinction is made between mechanical nonlinearity (related in the model to membrane velocity) and neural excitatory signal (related in the model to first or second spatial derivative of membrane displacement). Forf1(frequency of exciting tone) equal to CF (characteristic frequency), the model successfully reproduces the physiologically observed distinction betweenf2(frequency of suppressing tone) greater than CF andf2

ISSN:0001-4966    

DOI:10.1121/1.381369

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A set of experiments which assesses the ability of human observers to monitor two earphone channels for the purpose of performing one or two independent and simultaneous frequency difference‐limen tasks is described. Performance (d′) was significantly poorer with dichotic stimulus presentation than with monaural, control conditions. Under dichotic presentation conditions, performance was equivalent whether the observers were instructed to listen to one or both channels. A detailed analysis of the data indicated that the observers could discriminate a change but seemed to have difficulty in identifying the channel in which the change occurred. Consistent with results reported in the simultaneous signal‐detection literature using intensity detection or discriminations, we found that observers cannot successfully monitor more than one channel. It is suggested that when the dichotic stimulus presentation provides useful information which is not present during monaural tasks (i.e., lateralization cues), observers may be able, using this added information, to perform a divided attention task with little or no apparent performance decrement relative to single‐channel tasks.

ISSN:0001-4966    

DOI:10.1121/1.381370

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

on four subjects, perception of the movement velocity of the fused auditory image (FI) was studied by means of click‐train dichotic stimulation with gradually changing interaural time delays. With the signal used, the subjects were able to perceive differences in the velocities of FI movement. Absolute velocity difference limens (DL’s) were determined on the assumption that FI movements was uniform and that its trajectory might be approximated by an arc of a circle. The velocity DL’s were found to be nearly linearly related to the velocity of FI movement and increased from 14°/sec to 140°/sec.

ISSN:0001-4966    

DOI:10.1121/1.381371

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Monaural minimum‐audible‐field (MAF) measurements were taken for five subjects at seven angles of source elevation, φ  (−60°?φ?+60°), in the lateral vertical plane containing the interaural axis. These measurements were made by automated ’’method of limits’’ threshold determinations, using narrow‐band random noise (center frequencies from 4 to 16 kHz), emitted from a special ’’point’’ source. A method was devised for extracting from the MAF data, functions which display the elevation‐dependent changes in sensitivity, primarily caused by the pinna. Most of these derived functions contain a narrow response dip, whose minimum increases in frequency from ∠6.5 kHz monotonically to ∠14 kHz, with increasing source elevation. For corresponding elevations there are many intersubject similarities in these derived response functions and also strong agreement with known data regarding the pinna’s acoustic response. The percept of source elevation is hypothesized to be based upon the detection of the relative absence of specific high‐frequency spectral‐ energy content related to minima in the pinna’s response functions.

ISSN:0001-4966    

DOI:10.1121/1.381346

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

In an earlier paper, wqe examined the distribution of binaural resolvins power by measuring threshold increments of interaural delay as a function of overall dealy [E. R. Hafter and J. Demaio, J. Acoust. Soc. Am. 57, 181–187 (1975)]. In the current study, similar measures were made for interaural increments of intensity. As before, the stimuli were bandpass clicks of either low (0. 1–2 kHz) or hish (3–4 kHz) frequency. For overall interaural differences as sreat as 24 dB, it seems that performance was based on the interaural differences, and not on the monaural increments/decrements that are concommitant with a binaural change in level. As was the case with time, sensitivity to interaural intensity was reasonably constant across the range tested, indicating that, unlike the case for vision, spatial resolution in the auditory system is not concentrated in the center. A simple binaural trading ratio which converts intensity time can be shown to fit the data for low‐frequency clicks quite well. However, the fit to high frequencies is so poor as to suggest that separate mechanisms were used for detecting time and intensity.Finally, a number like the binaural masking‐level difference (MLD) was computed for the two kines of clicks. Suprisingly, the MLD’s for low and high frequencies were a similar 7.2 and 8.0 dB.

ISSN:0001-4966    

DOI:10.1121/1.381372

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Three experiments were conducted in order to compare the perception of the phonetic features of place and manner of articulation, specifically, the labial‐alveolar and the nasal‐stop distinctions. The results of experiment 1 showed that both features are perceived in a nearly categorical manner, with within‐category discrimination performance being quite poor compared to cross‐category performance in each case. Experiment 2, which used a selective adaptation paradigm, indicated that for each of these features there exist channels of analysis that are sensitive to the critical information specifying the contrast and that these channels operate in a context‐ conditioned fashion. Finally, in experiment 3, a right‐ear advantage was obtained for both place and manner, implicating the left hemisphere in the processing of each of these features. Taken together, the results of the three studies provide strong support for the claim that the place and manner features undergo similar forms of processing, even though they are specified by very different acoustic parameters.

ISSN:0001-4966    

DOI:10.1121/1.381373

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The paper discusses the temporal behavior of all measurable consonants, detailed in all possible conditions, in an extensive reading by one speaker. The data indicate a strong parallelism in duration distributions among similar kinds of consonants, and interesting similarities and differences between different kinds of consonants in terms of phoneme‐sequential constraints and higher‐level linguistic factors.

ISSN:0001-4966    

DOI:10.1121/1.381374

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Design of pulse‐recording systems and evaluation criteria (method of analyzing the pulse signature) are investigated with the objective of defining optimal approaches to pulse signal analysis. A representative situation which this paper addresses is the modeling of acoustic emission (AE) pulse analysis as a nondestructive means of failure detection in which pulse density counting is presently the most common evaluative criterion. The instrumentation is modeled and selected analytical pulses are passed through the system. Two alternatives are considered here: frequency spectrum analysis, and time domain reconstruction of the pulse or pulse train (deconvolution). The pulse recording/analysis problem is modeled, and the various analysis techniques are considered. Within practical constraint optimal system designs are defined. It is shown that deconvolution of a pulse is a superior approach for transient pulse analysis. Reshaping of a transducer output back of the original input pulse is possible and gives an accurate representation of the generating pulse in the time domain. Frequency spectrum analysis methods and AE measurement systems have potential for segregation of different pulse shapes. Using deconvolution, in principle any definable transducer and filter system can be used to reconstruct pulse characteristics, i.e., to generate time domain signature. A number of major conclusions about the selection of design variables are made for general usage. In addition there are families of optimal selections for transducer and filter system parameters which give superior deconvoluted output signals. These may be significant when working with actual hardware and unknown characteristics. The optimal design results are new and possibly different from the expectations of engineers accustomed to working in the field of signal conditioning. In obtaining these results modern rational design techniques on a rather complex design problem are demonstrated.

ISSN:0001-4966    

DOI:10.1121/1.381338

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP