摘要:

The filtered-xLMS algorithm and its modified versions have been successfully applied in suppressing acoustic noise such as single and multiple tones and broadband random noise. This paper presents an adaptive algorithm based on the filtered-xLMS algorithm which may be applied in attenuating tonal acoustic noise. In the proposed method, the weights of the adaptive filter and estimation of the phase shift due to the acoustic path from a loudspeaker to a microphone are computed simultaneously for optimal control. The algorithm possesses advantages over other filtered-xLMS approaches in three aspects: (1) each frequency component is processed separately using an adaptive filter with two coefficients, (2) the convergence parameter for each sinusoid can be selected independently, and (3) the computational load can be reduced by eliminating the convolution process required to obtain the filtered reference signal. Simulation results for a single-input/single-output (SISO) environment demonstrate that the proposed method is robust to the changes of the acoustic path between the actuator and the microphone and outperforms the filtered-xLMS algorithm in simplicity and convergence speed.

ISSN:0001-4966    

DOI:10.1121/1.423276

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Relations are determined between one of the important subjective attributes of concert hall acoustics, the apparent source width, ASW, and three acoustical measures, interaural cross-correlation coefficientIACCE,LFE,and strength factorG.Although these measures previously have been found to correlate with ASW, their relations with it have not been examined sufficiently, especially in respect to their frequency characteristics. Herein, ASW’s are directly determined for electronically reproduced musical sound fields with extensive ranges of values forIACCEandLFE.Investigated as parameters are angles of incidence, the time delay difference between a pair of symmetric early lateral reflections, and the number of early lateral reflections. These studies indicate the relative efficacy ofIACCEandLFEfor determining ASW under conditions that are realistically encountered in concert halls. The results were compared with measuredIACCE’s,LFE’s, and also the strength factorG’s in existing concert halls. It is concluded that the arithmetic average of[1−IACCE]’s at 500, 1 k and 2 k Hz combined with the strength factorGlowof the sound field at frequencies below 250 Hz are physical measures highly correlated with the subjective rank ordering of concert halls and that they cover the effects on ASW of the entire octave-band frequency range from 125 to 4 k Hz.

ISSN:0001-4966    

DOI:10.1121/1.423955

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The results of a systematic study investigating the effect on the sound insulation of wood stud walls having penetrations made by electrical outlet boxes are presented. The effect on sound insulation is shown to be almost negligible, regardless of box separation, if the boxes are themselves airtight and form an airtight seal with the gypsum board surfaces. However, if the boxes are not airtight, then the degradation to the sound insulation is strongly dependent on the separation between the boxes. Other significant factors include the presence of cavity absorption, and its method of installation. A series of retrofits for poorly installed boxes is examined and show that commonly available devices for reducing airflow (and sound insulation) through electrical boxes can be very effective but are highly dependent on installation.

ISSN:0001-4966    

DOI:10.1121/1.423277

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Most acoustic sources found in the ocean environment are spatially complex and broadband. In the case of shallow water propagation, these source characteristics complicate the analysis of received acoustic data considerably. A common approach to the broadband problem is to decompose the received signal into a set of narrow-band lines. This then allows the problem to be treated as a multiplicity of narrow-band problems. Here a model-based approach is developed for the processing of data received on a vertical array from a broadband source where it is assumed that the propagation is governed by the normal-mode model. The goal of the processor is to provide an enhanced (filtered) version of the pressure at the array and the modal functions. Thus a pre-processor is actually developed, since one could think of several applications for these enhanced quantities such as localization, modal estimation, etc. It is well-known that in normal-mode theory a different modal structure evolves for each temporal frequency; thus it is not surprising that the model-based solution to this problem results in a scheme that requires a “bank” of narrow-band model-based processors—each with its own underlying modal structure for the narrow frequency band it operates over. The “optimal” Bayesian solution to the broadband pressure field enhancement and modal function extraction problem is developed. It is shown how this broadband processor can be implemented (using a suboptimal scheme) in pseudo real time due to its inherent parallel structure. A set of noisy broadband data is synthesized to demonstrate how to construct the processor and achieve a minimum variance (optimal Bayesian) design. It is shown that both broadband pressure-field and modal function estimates can be extracted illustrating the feasibility of this approach.

ISSN:0001-4966    

DOI:10.1121/1.423278

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The principal aim of this work is to estimate, or to approximate, the complexk-space spectrum of the wave field arriving on a linear array. First, using linear approximation, the location-dependent effect of the wave field magnitudes is modeled as an extra “loss” factor in the complex spectral variable. This complex spectrum model may provide a better description of the physical process and require less sensor elements than the real spectrum model because of the additional degree of freedom provided by the “loss” factor. A high-resolution algorithm combining the singular value decomposition method and the eigen-matrix pencil method is then employed to find the complex spectra representing the incoming real spectrum and the location dependent factors of multipath and multimode arrivals. Five key features (noise immunity, robustness, resolution, accuracy, and physical insight) of the proposed algorithm are studied using numerical examples.

ISSN:0001-4966    

DOI:10.1121/1.423279

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A location problem is considered where the sound which propagates along multipath are impractical to model because the environment is poorly known. The acoustic bandwidth is assumed to be large enough so that the cross-correlation functions between pairs of receivers contain multiple peaks from multipath. The highest peak may not correspond to the difference in path lengths between the source and the receivers. Using similarities in the patterns of peaks in auto- and cross-correlation functions, an algorithm is developed to identify which cross-correlation peak corresponds to the difference in first arrivals, which can be used for locating the source if these arrivals are straight. The similarities are expressed with new “correlation equations.” The number of lag-type correlation equations isO(R2N2), whereNis the typical number of multipath at each ofRreceivers. The correlation equations may be impractical to solve exactly. Accurate solutions are found in simulations for the numbers, relative travel times, and amplitudes of all the multipath with the aid of a new “augmented-template correlation function” which is a cross-correlation of nonnegative lags of an auto-correlation function with lags from a cross-correlation function. The technique relies on time series which are filtered to yield one dominant source.

ISSN:0001-4966    

DOI:10.1121/1.423257

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A new approach is introduced for self-focusing phased arrays through inhomogeneous media for therapeutic and imaging applications. This algorithm utilizes solutions to the inverse scattering problem to estimate the impulse response (Green’s function) of the desired focal point(s) at the elements of the array. This approach is a two-stage procedure, where in the first stage the Green’s functions is estimated from measurements of the scattered field taken outside the region of interest. In the second stage, these estimates are used in the pseudoinverse method to compute excitation weights satisfying predefined set of constraints on the structure of the field at the focus points. These scalar, complex valued excitation weights are used to modulate the incident field for retransmission. The pseudoinverse pattern synthesis method requires knowing the Green’s function between the focus points and the array, which is difficult to attain for an unknown inhomogeneous medium. However, the solution to the inverse scattering problem, the scattering function, can be used directly to compute the required inhomogeneous Green’s function. This inverse scattering based self-focusing is noninvasive and does not require a strong point scatterer at or near the desired focus point. It simply requires measurements of the scattered field outside the region of interest. It can be used for high resolution imaging and enhanced therapeutic effects through inhomogeneous media without making any assumptions on the shape, size, or location of the inhomogeneity. This technique is outlined and numerical simulations are shown which validate this technique for single and multiple focusing using a circular array.

ISSN:0001-4966    

DOI:10.1121/1.423291

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Distortion-product otoacoustic emissions were recorded from the tympanum of the grasshopper,Locusta migratoria. The hearing organ of this insect is in direct contact with the tympanum and does not contain sensory hair cells.2f1−f2distortions were measured for stimulus frequencies between 2–70 kHz. For frequencies between 3–9 kHz, the level of2f1–f2was 30–50 dB below the stimulus level.2f1−f2threshold curves calculated from distortion growth functions at differentf2frequencies are most sensitive between 3–9 kHz. These thresholds match the auditory sensitivity of low frequency receptor neurons in the ear [Römer, J. Comp. Physiol.109, 101–122 (1976)]. In contrast to vertebrates, the dependence of the2f1−f2level on the frequency ratiof2/f1did not show distinct maxima for mostf2frequencies. The distortion levels were largest for small ratios close to 1. The behavior of2f1−f2was significantly different for stimulus frequencies below and above 10 kHz. Below 10 kHz, the thresholds were more sensitive, the slope of distortion growth curves was shallower by a factor of at least 2, and the distortion levels reversibly decreased duringCO2-induced hypoxia. Nonlinear mechanical processing may therefore be a general feature of sensitive hearing organs, even if these involve very different morphologies. Our results suggest that the the ciliated dendrites of the receptor cells of the insect may play a role in distortion generation.

ISSN:0001-4966    

DOI:10.1121/1.423258

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The frequency spectrum of a spontaneous otoacoustic emission (SOAE) recording may contain multiple narrow peaks. These peaks correspond to multiple SOAEs emitted by the inner ear. The individual SOAEs exhibit small amplitude fluctuations. The correlation between the amplitude fluctuations of multiple SOAEs in an individual ear was studied in 19 SOAE recordings from humans. For 424 pairs of SOAEs, the normalized amplitude cross-correlation function was computed. Significant correlation was found in 63 pairs (15%): 34 pairs showed positive and 29 pairs showed negative correlation. Some SOAE pairs were part of an equally spaced triplet of emission peaks, with one SOAE apparently generated as a distortion product of the other two “primary” SOAEs. The occurrence of correlation between a distortion product SOAE and a “primary” SOAE was 56%. This is significantly higher than the occurrence of correlation for the entire set of SOAE pairs. In addition, the spectral width of the distortion product SOAE was correlated with the spectral width of the “primary” SOAEs(R=0.87,p<10−6).For 79% of the correlated SOAE pairs, the cross-correlation function peaked at positive time delay. This indicates that for these pairs the fluctuation of the lower frequency emission lagged the fluctuation of the higher frequency emission. The average peak delay was 11.0 ms (s.d. 22.1 ms). The results demonstrate that interactions between SOAEs in an individual ear frequently occur and are asymmetrical.

ISSN:0001-4966    

DOI:10.1121/1.423259

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

This study examined the transient-evoked otoacoustic emission obtained in response to a click stimulus presented in combination with a pure tone in the guinea pig. Low-pass filtered click waveforms were digitally generated using asin(t)/tfunction windowed over 3 ms with an elevated cosine envelope. Transient-evoked otoacoustic emissions were obtained using the nonlinear derived response technique. Phase locked pure tones of various frequencies at∼70 dB SPLwere electrically mixed with electrical clicks, with the pure tone present only for the three lower level stimuli in the train of four stimuli. Enhancement in the amplitude of the response spectrum at frequencies which corresponded to regions of the basilar membrane apical to the tone was observed with the addition of the tone. This finding is inconsistent with the transient-evoked otoacoustic emission being the result of independent generators. It suggests that intermodulation distortion energy may contribute to the transient-evoked otoacoustic emission, the enhancement in the emission response spectrum at frequencies below the pure tone being a result of a complex interaction on the basilar membrane of intermodulation distortion products.

ISSN:0001-4966    

DOI:10.1121/1.423243

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP