Low-frequency Narrowband Noise Research Articles

An improved parallel narrowband active noise control system with local on-line secondary-path modeling equipped with frequency estimation algorithm

Active noise control technology shows good performance in those low-frequency narrowband noise control applications. Suffering from time-varying frequencies and secondary path, the performance of narrowband active noise control system may deteriorate seriously. In this work, an improved narrowband active noise control system is proposed to improve the noise reduction performance in those time-varying system. In the improved system, a frequency tracker based on the adaptive notch filter is adopted to estimate the frequencies of the noise signal. The result of frequency estimation is used to generate the reference signal and the prior information of the secondary-path modeling process. Then, the local secondary-path modeling can be conducted in the system with unknown fixed tonal noise signal or time-varying tones. Simulations and experiments are conducted to verify the performance of the proposed algorithm, and the results show that the proposed algorithm has good behavior.

The Onset-Offset N1-P2 Cortical Auditory Evoked Response in Individuals With High-Frequency Sensorineural Hearing Loss: Responses to High- and Low-Frequency Narrowband Noise.

This study aimed to determine whether onset-offset N1-P2 auditory evoked responses differ in amplitude, latency, and offset-to-onset trough-to-peak N1-P2 amplitude ratios (OOAR) between normal hearing (NH) sensitivity and moderate high-frequency sensorineural hearing loss (HFSNHL) groups when stimuli target regions of peripheral hearing sensitivity where the groups are in the normal range (i.e., 500 Hz) versus where they differ regarding presence of hearing loss (i.e., 4000 Hz). Onset-offset N1-P2 auditory evoked responses were measured from 10 participants with normal hearing sensitivity and seven participants with moderate HFSNHL using 500-Hz and 4000-Hz narrowband noise (NBN) stimuli. Stimuli were 2000 ms with 40-ms rise-fall times presented at 50 dB SL referenced to stimulus behavioral thresholds. Amplitudes and latencies were analyzed for N1 and P2 onset and offset components via repeated measures analysis of variance (ANOVA). OOARs were compared between groups using one-way ANOVA and across stimuli per group using paired samples t tests. Despite dB SPL stimulus presentation differences between groups, there were no significant differences in individual/absolute amplitude and latency waveform components between groups for either stimulus. Derived comparative calculations of OOAR for 4000-Hz NBN were significantly larger (p < .025; NH: .39; HFSNHL: .62) for the group with HFSNHL than the group with NH sensitivity; 500-Hz NBN OOAR did not reach significance. OOARs revealed no significant difference between stimuli for the group with normal hearing sensitivity, with .38 OOAR for both stimuli (p = .961). OOAR comparisons for the HFSNHL group across stimuli were significant (p = .012), with the 4000-Hz NBN OOAR being nearly double the size of the 500-Hz NBN OOAR. OOARs may provide insight to the balance of excitatory and inhibitory neural firing in the central auditory nervous system (CANS). Larger OOARs may be a biomarker of reduced CANS inhibition, perhaps indicative of a homeostatic central auditory gain mechanism.

Study on characteristics of flow structure and generation of narrow-band in low-frequency noise for a slat

Low-frequency narrow-band noise is one of the important components in the slat noise. Based on the transient flow field analysis for multi-element airfoil 30P-30N, the main mode characteristics of the slat pressure fluctuation are analyzed by means of proper orthogonal decomposition (POD) and dynamic model decomposition (DMD), and the key feature modes and the distribution of narrow-band frequencies for the slat are obtained. Empirical mode decomposition (EMD) and cross-correlation analysis are used to reconstruct the signal by preserving the low frequency characteristics of the original transient pressure signal. The locations of noise sources of the low-frequency narrow-band are determined according to the delay time and geometric relationship for characteristic points. The results show that the low-frequency narrow-band sound sources are mainly concentrated on regions of feature modes with large pressure fluctuations, such as slat trailing edge, downstream of the shear layer and the recirculation zone. Meanwhile, there are still some sound sources of low-frequency narrow-band distributed in regions of non-featured modes. The key characteristics of these regions are the interaction of flow structure between the trailing edge of the slat and the leading edge of the main wing due to collision of the shear layer.

1205 自動車ドアミラー周りの流れ場と空力騒音に関する研究

In order to reproduce the real driving condition of an automobile in the laboratory, the door mirror noise of the automobile was estimated by the wind tunnel test giving the uniform flow. Moreover, the scale model of the door mirror was analyzed by the wind tunnel for clarifying the relationship between the flow field around the door mirror and the aerodynamic noise. In particular, we discussed the low frequency narrow band noise and the flow field around the door mirror because the noise was 10dB larger than the background noise in the real automobile wind tunnel test. The experimental results indicated that when the clearance between the base and the visor of the door mirror is changed it influenced to the noise level in the low frequency domain. The noise level was increased due to the width of the wake when the clearance between the base and the visor was increased. From above results, we could grasp the phenomena about the narrow band noise in the vicinity of the 300 Hz generated from the actual automobile door mirror as it caused by the vortex shedding from the base.

Separating the Contributions of Olivocochlear and Middle Ear Muscle Reflexes in Modulation of Distortion Product Otoacoustic Emission Levels

Objectives: Mediated by the medial olivocochlear system (MOCS), distortion product otoacoustic emission (DPOAE) levels are reduced by presentation of contralateral acoustic stimuli. Such acoustic signals can also evoke a middle ear muscle reflex (MEMR) that also attenuates recorded DPOAE levels. Our aim is to clearly differentiate these two inhibitory mechanisms and to analyze each separately, perhaps allowing the development of novel tests of hearing function. Methods: DPOAE were recorded in real time from chinchillas with normal auditory brainstem response thresholds and middle ear function. Amplitude reduction and its onset latency caused by contralateral presentation of intermittent narrow-band noise (NBN) were measured. Stapedius and tensor tympani muscle tendons were divided without disturbing the ossicular chain, and DPOAE testing was repeated. Results: Peak reduction of (2f₁ - f₂) DPOAE levels occurred when the center frequency of contralateral NBN approximated the primary tone f₂, indicating an f₂-frequency-specific response. For a 4.5-kHz centered NBN, DPOAE (f₂ = 4.4 kHz) inhibition was 0.1 dB (p < 0.001). This response remained present after tendon division, consistent with an MOCS origin. Low-frequency NBN (center frequency: 0.5 kHz) reduced otoacoustic emission levels (0.1 dB, p < 0.001) across a wide range of DPOAE frequencies. This low-frequency response was abolished by division of the middle ear muscle tendons, clearly indicating MEMR involvement. Conclusions: Following middle ear muscle tendon division, DPOAE inhibition by contralateral stimuli approximating the primary tone f₂ persists, whereas responses evoked by lower contralateral frequencies are abolished. This distinguishes the different roles of the MOCS (f₂ frequency specific) and MEMR (low frequency only) in contralateral modulation of DPOAE. This analysis helps clarify the pathways involved in an objective test that might have clinical benefit in the testing of neonates.

Sub-inertial modulation of nonlinear Kelvin waves in the coastal zone

Abstract. Observational evidence is presented for interaction between nonlinear internal Kelvin waves at the ωt,i (where the ωt is the semidiurnal frequency and the ωi is the inertial frequency) and random oscillations of the background coastal current at the sub-inertial Ω frequency in the Japan/East Sea. Enhanced coastal currents at the sum ω+ and difference ω-frequencies ω±=ωt,i ± Ω have properties of propagating Kelvin waves, which suggests permanent energy exchange from the sub-inertial band to the mesoscale ω± band. This interaction may be responsible for a greater-than-predicted intensification, steepening and breaking of boundary-trapped Kelvin waves. The problem of interaction between the nonlinear Kelvin wave at the frequency ω and the low-frequency narrowband noise with representative frequency Ω&amp;amp;ll;ω is investigated using the theory of nonlinear weak dispersion waves.

Factors affecting the use of envelope interaural time differences in reverberation

At high frequencies, interaural time differences (ITDs) are conveyed by the sound envelope. Sensitivity to envelope ITDs depends crucially on the envelope shape. Reverberation degrades the envelope shape, reducing the modulation depth of the envelope and the slope of its flanks. Reverberation also reduces the envelope interaural coherence (i.e., the similarity of the envelopes at two ears). The current study investigates the extent to which these changes affect sensitivity to envelope ITDs. The first experiment measured ITD discrimination thresholds at low and high frequencies in a simulated room. The stimulus was either a low-frequency narrowband noise or the same noise transposed to a higher frequency. The results suggest that the effect of reverberation on ITD thresholds was multiplicative. Given that the threshold without reverberation was larger for the transposed than for the low-frequency stimulus, this meant that, in absolute terms, the thresholds for the transposed stimulus showed a much greater increase due to reverberation than those for the low-frequency stimulus. Three further experiments indicated that the effect of reverberation on the envelope ITD thresholds was due to the combined effect of the reduction in the envelope modulation depth and slopes, as well as the decrease in the envelope interaural coherence.

Differences between psychoacoustic and frequency following response measures of distortion tone level and masking

The scalp-recorded frequency following response (FFR) in humans was measured for a 244-Hz pure tone at a range of input levels and for complex tones containing harmonics 2-4 of a 300-Hz fundamental, but shifted by ±56 Hz. The effective magnitude of the cubic difference tone (CDT) and the quadratic difference tone (QDT, at F(2)-F(1)) in the FFR for the complex was estimated by comparing the magnitude spectrum of the FFR at the distortion product (DP) frequency with that for the pure tone. The effective DP levels in the FFR were higher than those commonly estimated in psychophysical experiments, indicating contributions to the DP in the FFR in addition to the audible propagated component. A low-frequency narrowband noise masker reduced the magnitude of FFR responses to the CDT but also to primary components over a wide range of frequencies. The results indicate that audible DPs may contribute very little to the DPs observed in the FFR and that using a narrowband noise for the purpose of masking audible DPs can have undesired effects on the FFR over a wide frequency range. The results are consistent with the notion that broadly tuned mechanisms central to the auditory nerve strongly influence the FFR.

Open-Loop Adaptive Filter for Power Electronics Applications

An open-loop adaptive filter, which can be used in various power electronics control systems, is presented. The purpose of the filter is to give as fast a step response as possible while retaining good noise canceling properties. The proposed filter consists of a first-order infinite-impulse-response filter, the coefficients of which are adapted according to the changes in the input signal. In particular, good performance is obtained if the filter must suppress a low-frequency narrow-band noise. The performance of the filter is verified through step response simulations and with a laboratory prototype of a welding machine. The control system of the prototype is implemented on a field-programmable gate array. The proposed filter is compared to two optimum linear filters: (1) the moving average filter and (2) a filter whose step response and white noise gain are both optimized. The step response simulations show that, with the proposed filter, the step response time can be considerably decreased compared to these filters. The prototype also shows that, when using the proposed filter, the step response of the welding current can be made better than that of the original analog control.

Effect of Ipsilateral and Contralateral Low-frequency Narrow-band Noise on Temporary Threshold Shift in Humans

Objective – To evaluate the effect of ipsilateral and contralateral low-frequency (250 Hz) narrow-band noise (NBN) on the temporary threshold shift (TTS) induced by a 2 kHz tone in young normally hearing subjects with a functioning auditory efferent system.Material and Methods – Sixteen young volunteers served as subjects. All the subjects were young (20–30 years), disease-free and had a medical history negative for otological disease, noise exposure and use of ototoxic drugs. They had normal hearing [thresholds of 125–8000 Hz below 20 dB hearing level (HL)], transient-evoked otoacoustic emissions and contralateral suppression. The subjects were randomly assigned to one of three different groups. Subjects in Group A (n=5) were exposed to a 90 dB HL 2 kHz pure tone for 10 min. Subjects in Group B (n=6) were exposed to a 90 dB HL 2 kHz pure tone and an ipsilateral 45 dB HL 250 Hz NBN for 10 min. Subjects in Group C (n=5) were exposed to a 90 dB HL 2 kHz pure tone and a contralateral 45 dB HL 250 Hz NBN for 10 min. The right ear served as the test ear. The TTS 2 min after the end of the exposure (TTS2) was measured in all subjects at 2, 3 and 4 kHz.Results – TTS2 in Group A was significantly higher at 3 kHz (p=0.011) and at 4 kHz (p=0.003) than TTS2 in Group B. At 4 kHz, TTS2 in Group C was significantly higher (p=0.013) than TTS2 in Group B. Although TTS2 in Group C was lower than TTS2 in Group A, this difference was not significant. The presence of an ipsilateral low-frequency NBN significantly reduced TTS2 induced by a 90 dB HL 2 kHz tone. A contralateral low-frequency NBN reduced TTS2 in this group of subjects; however, the reduction was not significant.Conclusion – The results of this study show that an ipsilateral low-intensity, low-frequency (250 Hz) NBN can give protection from a TTS induced by a 2 kHz tone. Contralateral low-frequency NBN did not induce any protective effect.

Sound lateralization and interaural discrimination.: Effects of brainstem infarcts and multiple sclerosis lesions

Subjects with brainstem lesions due to either an infarct or multiple sclerosis (MS) underwent two types of binaural testing (lateralization testing and interaural discrimination) for three types of sounds (clicks and high and low frequency narrow-band noise) with two kinds of interaural differences (level and time). Two major types of abnormalities were revealed in the lateralization performances: perception of all stimuli, regardless of interaural differences (time and/or level) in the center of the head (center-oriented), or lateralization of all stimuli to one side or the other of the head (side-oriented). Similar patterns of abnormal lateralization (center-oriented and side-oriented) occurred for MS and stroke patients. A subject’s pattern of abnormal lateralization testing was the same regardless of the type of stimulus or type of interaural disparity. Lateralization testing was a more sensitive test than interaural discrimination testing for both types of subjects. Magnetic resonance image (MRI) scanning in three orthogonal planes of the brainstem was used to detect lesions. A semi-automated algorithm superimposed the auditory pathway onto each MRI section. Whenever a lesion overlapped the auditory pathway, some binaural performance was abnormal and vice versa. Given a lateralization test abnormality, whether the pattern was center-oriented or side-oriented was mainly determined by lesion site. Center-oriented performance was principally associated with caudal pontine lesions and side-oriented performance with lesions rostral to the superior olivary complex. For lesions restricted to the lateral lemniscus and/or inferior colliculus, whether unilateral or bilateral, just noticeable differences (JNDs) were nearly always abnormal, but for caudal pontine lesions JNDs could be normal or abnormal. MS subjects were more sensitive to interaural time delays than interaural level differences particularly for caudal pontine lesions, while stroke patients showed no differential sensitivity to the two kinds of interaural differences. These results suggest that neural processing of binaural stimuli is multilevel and begins with independent interaural time and level analyzers in the caudal pons.

Membrane potential responses of supragranular pyramidal neurons to sound stimuli in cat primary auditory cortex

Subjects with brainstem lesions due to either an infarct or multiple sclerosis (MS) underwent two types of binaural testing (lateralization testing and interaural discrimination) for three types of sounds (clicks and high and low frequency narrow-band noise) with two kinds of interaural differences (level and time). Two major types of abnormalities were revealed in the lateralization performances: perception of all stimuli, regardless of interaural differences (time and/or level) in the center of the head (center-oriented), or lateralization of all stimuli to one side or the other of the head (side-oriented). Similar patterns of abnormal lateralization (center-oriented and side-oriented) occurred for MS and stroke patients. A subject’s pattern of abnormal lateralization testing was the same regardless of the type of stimulus or type of interaural disparity. Lateralization testing was a more sensitive test than interaural discrimination testing for both types of subjects. Magnetic resonance image (MRI) scanning in three orthogonal planes of the brainstem was used to detect lesions. A semi-automated algorithm superimposed the auditory pathway onto each MRI section. Whenever a lesion overlapped the auditory pathway, some binaural performance was abnormal and vice versa. Given a lateralization test abnormality, whether the pattern was center-oriented or side-oriented was mainly determined by lesion site. Center-oriented performance was principally associated with caudal pontine lesions and side-oriented performance with lesions rostral to the superior olivary complex. For lesions restricted to the lateral lemniscus and/or inferior colliculus, whether unilateral or bilateral, just noticeable differences (JNDs) were nearly always abnormal, but for caudal pontine lesions JNDs could be normal or abnormal. MS subjects were more sensitive to interaural time delays than interaural level differences particularly for caudal pontine lesions, while stroke patients showed no differential sensitivity to the two kinds of interaural differences. These results suggest that neural processing of binaural stimuli is multilevel and begins with independent interaural time and level analyzers in the caudal pons.

Optical imaging of neural coding of interaural time differences in the rat's superior olivary complex

Subjects with brainstem lesions due to either an infarct or multiple sclerosis (MS) underwent two types of binaural testing (lateralization testing and interaural discrimination) for three types of sounds (clicks and high and low frequency narrow-band noise) with two kinds of interaural differences (level and time). Two major types of abnormalities were revealed in the lateralization performances: perception of all stimuli, regardless of interaural differences (time and/or level) in the center of the head (center-oriented), or lateralization of all stimuli to one side or the other of the head (side-oriented). Similar patterns of abnormal lateralization (center-oriented and side-oriented) occurred for MS and stroke patients. A subject’s pattern of abnormal lateralization testing was the same regardless of the type of stimulus or type of interaural disparity. Lateralization testing was a more sensitive test than interaural discrimination testing for both types of subjects. Magnetic resonance image (MRI) scanning in three orthogonal planes of the brainstem was used to detect lesions. A semi-automated algorithm superimposed the auditory pathway onto each MRI section. Whenever a lesion overlapped the auditory pathway, some binaural performance was abnormal and vice versa. Given a lateralization test abnormality, whether the pattern was center-oriented or side-oriented was mainly determined by lesion site. Center-oriented performance was principally associated with caudal pontine lesions and side-oriented performance with lesions rostral to the superior olivary complex. For lesions restricted to the lateral lemniscus and/or inferior colliculus, whether unilateral or bilateral, just noticeable differences (JNDs) were nearly always abnormal, but for caudal pontine lesions JNDs could be normal or abnormal. MS subjects were more sensitive to interaural time delays than interaural level differences particularly for caudal pontine lesions, while stroke patients showed no differential sensitivity to the two kinds of interaural differences. These results suggest that neural processing of binaural stimuli is multilevel and begins with independent interaural time and level analyzers in the caudal pons.

Relationship between psychophysical tuning curves and "suppression".

This study examined two-tone unmasking and auditory frequency selectivity about 3 kHz for the purpose of demonstrating a qualitative relationship between the two. An adaptive 2IFC forward-masking procedure was used to collect psychophysical tuning curves (PTC's) and two-tone masking data under a quiet and noise condition for the same normal-hearing listeners. In the noise condition, a narrowband noise masker, centered one decade down from the probe, was gated on with the tonal masker(s). Kiang and Moxon [J. Acoust. Soc. Am. 55, 620-630 (1974)] have found that low-frequency narrowband noise serves to decrease the sharpness of electrophysiological tuning curves by affecting only the tip segments. The data for four highly practiced listeners indicate that the gated-noise masker was effective in broadening the PTC's and in lessening the magnitude of two-tone unmasking. The mutually reflected changes in tuning curves and in two-tone unmasking indicate a close relationship between frequency selectivity and unmasking: the greater the magnitude of unmasking above the center frequency of the PTC, the sharper the tuning of the PTC.