Presence Of Broadband Noise Research Articles

Three psychophysical metrics of auditory temporal integration in macaques.

The relationship between sound duration and detection threshold has long been thought to reflect temporal integration. Reports of species differences in this relationship are equivocal: some meta-analyses report no species differences, whereas others report substantial differences, particularly between humans and their close phylogenetic relatives, macaques. This renders translational work in macaques problematic. To reevaluate this difference, tone detection performance was measured in macaques using a go/no-go reaction time (RT) task at various tone durations and in the presence of broadband noise (BBN). Detection thresholds, RTs, and the dynamic range (DR) of the psychometric function decreased as the tone duration increased. The threshold by duration trends suggest macaques integrate at a similar rate to humans. The RT trends also resemble human data and are the first reported in animals. Whereas the BBN did not affect how the threshold or RT changed with the duration, it substantially reduced the DR at short durations. A probabilistic Poisson model replicated the effects of duration on threshold and DR and required integration from multiple simulated auditory nerve fibers to explain the performance at shorter durations. These data suggest that, contrary to previous studies, macaques are uniquely well-suited to model human temporal integration and form the baseline for future neurophysiological studies.

DPOAE Measurements at Frequency Fine Structure Before and After Contralateral Suppression

The purpose of this study was to investigate distortion product otoacoustic emission (DPOAE) measurements before and after contralateral suppression at frequency fine structure. 8pts/octave DP-gram was measured at f2 frequencies ranging from 841 Hz to 8,000 Hz in fifty six ears of normal hearing adults with and without contralateral broad band noise (BBN) at 70 dB SPL. The data were analyzed depending on groups by gender, age(20's, 30's, and 40's+) and directions of the ear. Results showed the followings: (1) DPOAE amplitude was decreased significantly with presence of broad band noise, showing contralateral suppression. (2) At the frequency fine structure, change in DPOAE amplitude before and after suppression was significant. The great amplitude change was observed between 1,000 and 2,000 Hz for most participants. (3) Change in DPOAE amplitude before and after suppression was not significant depending on gender and age, but was significant depending on directions of the ear. (4) Change in DPOAE amplitude before and after suppression was significant for peak and dip frequencies. Also, change in DPOAE amplitude was mostly suppressed at the peak frequencies, however, change in DPOAE amplitude was varied at the dip frequencies. A larger inter-subject variability was observed in the dip frequencies. The results suggest that measuring DPOAE contralateral suppression at peak frequencies in DPOAE would improve efficiency of the auditory efferent system assessment.

Decoherence times of universal two-qubit gates in the presence of broad-band noise

The controlled generation of entangled states of two quantum bits is a fundamental step toward the implementation of a quantum information processor. In nano-devices this operation is counteracted by the solid-state environment, characterized by a broadband and non-monotonic power spectrum, often 1/f, at low frequencies. For single-qubit gates, incoherent processes due to fluctuations acting on different time scales result in peculiar short- and long-time behavior. Markovian noise gives rise to exponential decay with relaxation and decoherence times, T1 and T2, simply related to the symmetry of the qubit–environment coupling Hamiltonian. Noise with the 1/f power spectrum at low frequencies is instead responsible for defocusing processes and algebraic short-time behavior. In this paper, we identify the relevant decoherence times of an entangling operation due to the different decoherence channels originating from solid-state noise. Entanglement is quantified by concurrence, which we evaluate in an analytic form employing a multi-stage approach. The ‘optimal’ operating conditions of reduced sensitivity to noise sources are identified. We apply this analysis to a superconducting gate for experimental noise spectra.

A comparison between contralateral suppression in cochlear microphonics and distortion product otoacoustic emissions.

This study compares the contralateral suppressive effect of the auditory efferent system on cochlear microphonics versus distortion-product OAEs (DPOAEs) in order to identify the potential versus the mechanical changes of the outer hair cells. This was achieved by recording the CM and DPOAEs from the right ear of 16 normal-hearing young female adults with and without broad band noise (BBN) in the left ears. DPOAEs were recorded at 0.5, 2, and 4 kHz F2 frequencies, and at 0.5 and 2 kHz tone bursts and clicks for CM using condensation and rarefaction polarity. Results revealed that both DPOAEs and CM recordings showed suppression and enhancement effects of BBN, but there were no statistically significant differences within each recording (with-without BBN) and between recordings (CM versus DPOAEs) (P = 0.923 at 0.5 kHz, P = 0.858 at 2 kHz, and P = 0.332 at 4 kHz or clicks). This could be related to the small effect and the lack of sensitive enough equipment. In general, larger effect was observed at 0.5 kHz in DPOAEs, but at 2 kHz in CM. Interestingly, when the stimulus polarity of the CM was changed from condensation to rarefaction at 2 kHz in the presence of BBN, six participants showed CM recordings that changed from suppression to enhancement or vice versa, suggesting a possible relationship.

Study on the Selection of Specific Filters for Enhancement of Recorded Speech for Speaker Identification

Understanding the noise characteristics for finding appropriate filtering technique/s so as to obtain sufficiently clear speech samples for Speaker Identification, is one of the challenging tasks in Forensic Acoustics. Speaker's idiosyncratic speech should not be affected when the noise reduction is carried out; otherwise, Speaker Identification becomes highly erroneous. We have collected fifty noisy speech samples reported to be recorded in different modes from actual crime cases received in the laboratory. The samples are analyzed after subjecting to various filtering techniques and compared with the clear speech mixed with the noise collected from non-speech portion. Distortion levels on the speech are studied at various stages of application of filters in terms of SNR and Speaker Specific Information. Retaining the Speaker Specific Information as primary concern of our study, the limitation of filtering techniques depending on the characteristic and intensity level of noise is worked out for noisy speech samples. Subsequently a statistical study is also conducted. Listening tests were conducted to ensure that the perceptual features of the original noisy speech are preserved while applying filters. This work demonstrates the efficiency of Noise reduction filters in improving SNR and their controlled applications for preserving Speaker dependent features depending on the various noise characteristics embedded on speech samples. Audio Forensics has a challenging history of enhancement problems of speech samples received for examination. It is observed that out of the total speech samples received for Speaker Identification in the Laboratory, a large number of recordings requires enhancement. Speech is a non-linear time series represented in terms of complex number. Hence separating noise from noisy speech in spectral domain results into countless solutions. The main objective of a Noise Cancellation system is to obtain a clear signal with higher quality of speech signal. The presence of noise in speech signals can create higher degree of mismatch in performance of speech processing systems used for Speaker Identification as well as Speech Recognition. Inappropriate filtering of noise corresponds to extracting features of noise together with the actual speech signal during the feature extraction process. However, the desired parametric representation carries a high amount of error rate. The presence of broadband noise and a very low SNR deteriorate the intelligibility of most of the recorded speech samples. Speaker's idiosyncratic speech is affected when the noise reduction is carried out. Thus the Speaker Identification

Identification and classification of resonant targets with iterative, single-channel time reversal in a noisy environment

The identification and classification of mines resting on and buried beneath the sea floor is an important and challenging problem. Previous numerical results indicate that iterative time reversal using a single-element transducer increases the signal-to-noise ratio of the backscattered return while simultaneously converging to a narrow-band signal characteristic of the scattering target [D. M. Pierson, ‘‘Buried object detection using time-reversed acoustics,’’ Ph.D. dissertation, North Carolina State University 2003]. This technique offers an inexpensive and simple means for maximizing signal level in a noisy or cluttered environment. We investigate this phenomena through experiments performed in a water tank using a 6.35-mm-diam hollow steel sphere and broadband Q∼1.5) piston transducers operating in the 100-kHz to 2-MHz frequency range. Time-reversal convergence of the interrogation pulse was readily achieved using a variety of broadband (0.1–2 MHz) pulses to initiate the process. Results indicate that the spectrum of the echo rapidly converges to the dominant resonant mode of the target, with a significant enhancement in signal level even in the presence of broadband noise and coherent clutter returns. [Work supported by Office of Naval Research Award No. N000140610044.]

A Psychophysical Evaluation of Spectral Enhancement

Listeners with sensorineural hearing loss have well-documented elevated hearing thresholds; reduced auditory dynamic ranges; and reduced spectral (or frequency) resolution that may reduce speech intelligibility, especially in the presence of competing sounds. Amplification and amplitude compression partially compensate for elevated thresholds and reduced dynamic ranges but do not remediate the loss in spectral resolution. Spectral-enhancement processing algorithms have been developed that putatively compensate for decreased spectral resolution by increasing the spectral contrast, or the peak-to-trough ratio, of the speech spectrum. Several implementations have been proposed, with mixed success. It is unclear whether the lack of strong success was due to specific implementation parameters or whether the concept of spectral enhancement is fundamentally flawed. The goal of this study was to resolve this ambiguity by testing the effects of spectral enhancement on detection and discrimination of simple, well-defined signals. To that end, groups of normal-hearing (NH) and hearing-impaired (HI) participants listened in 2 psychophysical experiments, including detection and frequency discrimination of narrowband noise signals in the presence of broadband noise. The NH and HI listeners showed an improved ability to detect and discriminate narrowband increments when there were spectral decrements (notches) surrounding the narrowband signals. Spectral enhancements restored increment detection thresholds to within the normal range when both energy and spectral-profile cues were available to listeners. When only spectral-profile cues were available for frequency discrimination tasks, performance improved for HI listeners, but not all HI listeners reached normal levels of discrimination. These results suggest that listeners are able to take advantage of the local improvement in signal-to-noise ratio provided by the spectral decrements.

Operational Constraints on the Utility of Virtual Audio Cueing

The potential of virtual audio display technology to provide operators with veridical spatial cues may be substantially constrained by factors that are common in many operational settings – i.e., high noise level, limitations in the bandwidth of the audio source and/or display. The purpose of this study was to examine the effects of varying the bandwidth of a virtual sound source in the presence of broadband noise in a reverberant environment. Specifically, the signal-to-noise ratio (SNR) was varied from +50 dB to −10 dB, and the signal was low pass filtered at 1.6 kHz, 4 kHz, 8 kHz, and 15 kHz. Correlational analyses comparing actual and perceived sound source location revealed that both signal bandwidth and signal-to-noise ratio influenced auditory localization acuity, and that even under optimal bandwidth and noise conditions (15 kHz and +50 dB) localization in elevation was extremely poor. These findings have numerous implications for the design of spatial audio displays, especially those meant to be used in noisy environments.

A comparison of tonal signal extraction methods

The measurement of acoustic pressure signals in the presence of masking noise, often generated by mean flow, is a continual problem in the field of passive liner duct acoustics research. When performing acoustic liner tests in a flow duct facility, the researcher must balance two criteria. The most obvious is to design the acoustic liner such that the maximum amount of sound absorption is achieved. The other is to obtain a signal-to-noise ratio high enough for quality measurements. For grazing incidence impedance tests, these two criteria are contradictory. As the liner absorptive capacity is increased, the signal-to-noise ratio at the liner trailing edge is decreased. For this reason, measurement methods are needed that are capable of accurately extracting the portion of the measured acoustic pressure which is due to the sound source, even when the desired signal is buried beneath the broadband background noise generated by the presence of mean flow. The results to be presented provide a comparison study of three signal extraction methods for acquiring quality acoustic pressure measurements in the presence of broadband noise (to simulate effects of mean flow). The performance of each method was compared to a baseline measurement of a pure tone acoustic pressure 3 dB above a uniform, broadband noise background.

AR modeling of myoelectric interference signals during a ramp contraction.

We investigated the time-varying behaviour of the autoregressive (AR) parameters in a myoelectric (ME) signal detected during a linear force increasing contraction. The AR parameters of interest were the reflection coefficients, the AR model spectrum, and the prediction errors. We used well-conditioned ME signals for which the complete time record of the motor units firings was available. In addition, the influence of the recruitment of a new motor unit, the conduction velocity of action potentials, and additive broad-band noise were investigated using simulated ME signals. The simulated ME signals were constructed from a selected group of the available motor unit action potential trains. The results revealed that, as the contraction progressed, the AR parameters displayed a time-varying behavior which coincided with the recruitment of newly recruited motor units whose spectrum of the waveform differed from that of the rest of the ME signal. This property of the AR parameters was obscured by the presence of broad-band noise and low-amplitude motor unit action potentials, both of which are more pronounced during low-level force contractions.

Auditory filter shapes of normal-hearing and hearing-impaired listeners in continuous broadband noisea)

Listeners with sensorineural hearing impairment typically exhibit auditory processing deficits such as reduced frequency and/or temporal resolution. Such deficits may represent separate sequela of auditory pathology or may result directly from the sensitivity loss and the requirement to listen at high levels. To assess the impact of increased thresholds on frequency resolution, auditory filter characteristics were determined for hearing-impaired and normal-hearing listeners at 500 and 2000 Hz in the presence of continuous broadband noise meant as a rough simulation of hearing loss. In the fitting procedure, the low-frequency skirt of the derived auditory filter was allowed to vary as a function of signal level, permitting different filter shapes to be estimated at high versus low signal levels. Listeners with moderate hearing losses at 2000 Hz demonstrated near-normal auditory filter shapes for lower signal levels, but increasingly broad and asymmetric filters as signal level was raised. At 500 Hz, where hearing losses were mild, filter bandwidths increased little at the higher signal levels. The presence of broadband noise had essentially no effect on filter shapes of either listener group. The filter shape abnormalities demonstrated by listeners with moderate hearing loss, which were not observed in normal-hearing listeners at the same signal levels, indicate that poor frequency resolution in these patients for high-intensity stimuli does not follow directly from decreased sensitivity, but instead reflects an independent pathology.

Sensitivity of auditory nerve fibers to spectral notches

1. Listeners use direction-dependent spectral cues introduced by the torso, head, and pinnae to localize the source of a sound in space. Among the prominent direction-dependent spectral features in the free field-to-eardrum transfer function are narrow regions of low acoustic energy referred to as spectral notches. In this paper, we studied the sensitivity of single auditory nerve fibers in the barbiturate-anesthetized cat to broadband noise that had been filtered by a function whose shape approximated natural notches in the free field-to-eardrum transfer function. 2. Two experimental paradigms were employed. The first was the repeated presentation of a burst of broadband noise filtered by the simulated-notch function. Center frequency of the notch was held constant at or around the fiber characteristic frequency (CF). We refer to this as a "stationary" notch stimulus. The second paradigm was the repeated presentation of a broadband noise that was constructed from noise segments, each filtered by the simulated notch, whose CF was incremented and then decremented in a systematic way. We refer to this as a "moving" notch stimulus. Results from these two paradigms were compared with respect to notch detection. 3. Data were obtained from 161 single auditory nerve fibers having CFs ranging from 0.4 to 40 kHz. Most fibers studied had CFs > 5 kHz, and they detected the presence of the spectral notch in an intensity- and frequency-dependent manner. Each fiber responded vigorously to the presence of broadband noise. When the CF of the notch encroached on the response area of the fiber, there was a demonstrable reduction in discharge rate. The greatest reduction in discharge rate occurred when the notch was centered at the fiber's CF and when the level of the notch signal was some 15-55 dB above the fiber's noise threshold. There was close association in the frequency-intensity plane between the position of the most effective notch and the fiber's threshold tuning curve. 4. For high-spontaneous rate fibers, a moving-notch stimulus, but not a stationary one, reduced the discharge below the spontaneous rate at and in the immediate vicinity of the most effective notch frequency. This increases sensitivity to a spectral notch and suggests a mechanism by which localization ability is enhanced when there is relative motion between a sound source and the head.(ABSTRACT TRUNCATED AT 400 WORDS)

Frequency Selectivity for Hearing-Impaired and Broadband-noise-masked Normal Listeners

When evaluating frequency selectivity, it is difficult to determine if the deviation from normal performance observed for hearing-impaired listeners reflects abnormal cochlear function or normal, level-dependent changes in frequency selectivity. This experiment was designed to investigate the dependence of frequency-selectivity measures on threshold and signal level. Auditory-filter characteristics, critical ratios, forward-masked psychophysical tuning curves, and narrowband-noise masking patterns were obtained from normal-hearing listeners in quite and in the presence of broadband noise at five levels. These findings were then compared to previously obtained frequency-selectivity measurements for subjects with mild-to-moderate sensorineural hearing loss whose absolute thresholds are comparable to the normal-hearing listeners' masked thresholds. The results suggest that frequency selectivity deterioriates as threshold increases for all subjects. However, the poor frequency selectivity exhibited by hearing-impaired listeners may not be explained entirely by the effects of threshold and signal level. Nevertheless, because frequency selectivity is poorer in the normal auditory system at higher stimulus levels, the deviation from normal performance observed for hearing-impaired listeners may not be as large as previously suggested.

Detection of auditory sinusoides of fixed and uncertain frequency by budgerigars ( Melopsittacus undulatus) and zebra finches ( Poephila guttata)

Three budgerigars and three zebra finches were tested for their ability to detect sinusoidal stimuli in the presence of broadband noise. Masked thresholds for 1, 2, and 4 KHz pure tones were measured with a fixed frequency condition, in which only one test frequency was presented in a session and with an uncertain frequency condition, in which three signal frequencies were presented in random order in one session. The critical signal/noise ratios obtained in the fixed frequency condition were similar to those reported in a previous study (Okanoya and Dooling, 1987) for both species. When tested in the uncertain frequency condition, critical ratios for zebra finches increased for 1.5 dB at 1 KHz signal but remained unchanged 2 and 4 kHz. The critical ratios for budgerigars showed no difference at any frequency in the uncertain frequency condition. These results suggest that (1) budgerigars and zebra finches are similar in the degree to which attention factors are involved in the detection of signals in noise and (2) the unusual shape of the budgerigar critical ratio function is not the result of central attentional processes.

White noise and pure tone masking of pure tone thresholds of a harbour seal listening in air and underwater

Background noises mask the detection of sound throughout a limited frequency range termed the critical bandwidth. Critical bandwidths of a harbour seal (Phoca vitulina) were measured, using behavioural psychophysical techniques, by indirect (critical ratios) and direct (two-tone masking) methods underwater and in air. Underwater critical ratios were determined at 4, 8, 16, and 32 kHz, using white noise spectrum levels of 50, 56, 60, and (or) 70 dB re 1 μPa. The critical ratios (pooled data, threshold ±SD) were 19 ± 9, 22 ± 7, 25 ± 7, and 27 ± 5 dB for the respective frequencies. In-air critical ratios were determined at 2, 4, 8, and 16 kHz, using white noise spectrum levels ranging from 23 to 50 dB re 20 μPa. The critical ratios (pooled data) were 25 ± 8, 23 ± 10, 21 ± 15, and 23 ± 16 dB for the respective frequencies. The arithmetic mean of the critical ratios in both media was 23 dB. This suggests that the seal is equally sensitive to pure tone signals in the presence of broad band noise in both air and water. Direct measurements of the critical bandwidth underwater were determined at 4, 8, 16, and 32 kHz, using a pure tone masker ranging from 96 to 120 dB re 1 μPa. In-air direct measurements of the critical bandwidth were measured at 2, 4, and 8 kHz, using a pure tone masker set at 80 dB re 20 μPa. The bandwidths, estimated at 23 dB below the masking level, were all under 2.25 kHz and become proportionately narrow at higher frequencies. These results show a narrow critical bandwidth for the harbour seal, thus indicating high frequency resolution in both media. The directly measured critical bandwidths from the two-tone masking study were not 2.5 times the critical bandwidth estimated from the critical ratios, as previously reported in some other mammals.

Frequency resolution for broadband‐noise masked normal listeners

When evaluating frequency resolution of hearing‐impaired listeners, it is often difficult to determine if changes observed in auditory analysis with increasing auditory threshold reflect abnormal cochlear function or represent normal auditory processing at high stimulus levels. This experiment was designed to investigate the dependence of frequency‐resolution measures on threshold and signal level. Auditory‐filter characteristics, critical ratios, psychophysical tuning curves, and masking patterns were obtained from normal‐hearing listeners in quiet and in the presence of broadband noise at five levels (30 to 70 dB SPL). These findings were then compared to previously obtained frequency‐resolution results for subjects with sensorineural hearing loss whose auditory thresholds in quiet were comparable to the normal‐hearing listener's masked thresholds. These comparisons, while limited to individuals with moderate hearing loss and broadband‐noise masked normal listeners, suggest that frequency resolution observed in hearing‐impaired listeners is similar to that seen in the normal auditory system at high stimulus sound‐pressure levels. [Work supported by NIH NS 18015.]

Inner hair cell responses to tonal stimulation in the presence of broadband noise.

The effects of broadband noise (BBN) on the tone-evoked de receptor potential from inner hair cells of guinea pigs were measured. The effects of the noise were: suppression of the receptor potential, no net change, or greater depolarization relative to the tone alone, evoked receptor potential. The effects appear to be consistent with a two-tone suppression hypothesis. The time course of the suppression effect is immediate and constant in time. This observation suggests no obvious involvement of a local feedback loop in outer hair cells or one depending on the efferent nerves. Inner hair cell "sensitivity" is a variable in the magnitude of the suppression. Comparison of masked, tone-evoked de receptor potential intensity functions to responses from auditory-nerve fibers (taken from the literature for experiments using a similar paradigm) differentiates the phenomena of suppression and adaptation in the auditory periphery.

Profile analysis and background noise.

Spectral shape discrimination, or profile analysis, of complex waveforms (21 components) in the presence of broadband noise and special sinusoidal maskers of random amplitude was studied. The first experiment involved the discrimination between a standard flat spectrum and a "rippled" spectrum in broadband noise of different spectrum levels. Thresholds obtained under control conditions, without noise or without a standard, were used to estimate constants of an equation that predict thresholds where standard and noise are both present. The model assumes an external variance, produced by the noise, is added linearly to an internal variance caused by the flat standard. The mean squared error is less than 2 dB. The second experiment involved the detection of an increment on the center component of the 21-component standard. Added to the standard was an additional masking sinusoid of random amplitude. Both the frequency and the range of the random amplitude were varied and both showed a systematic influence on the detectability of the 1000-Hz increment.

Interaural correlation discrimination: II. Relation to binaural unmasking.

Many theoretical models of binaural interaction assume that sensitivity to interaural correlation underlies binaural unmasking. This paper explores the extent to which sensitivity to changes in interaural correlation implied by results from binaural detection experiments are consistent with sensitivity to changes in interaural correlation implied by results from binaural detection experiments are consistent with sensitivity to changes in interaural correlation measured directly in correlation discrimination experiments. The vehicle for this exploration is a simplified model of the underlying processes assumed by many models of binaural unmasking for the detection of narrow-band signals in the presence of broadband noise. Consideration is given to psychometric function slopes, detection thresholds, bandwidth effects, duration effects, level effects, and interaural-parameter effects. Although many of the results obtained from our analysis are consistent with the notion that the cue in binaural detection tasks is a change in interaural correlation, some significant inconsistencies are noted.

The effect of broadband noise on the human brainstem auditory evoked response. II. Frequency specificity.

A series of experiments evaluated the effects of broadband noise (ipsilateral) on wave V of the brainstem auditory evoked response (BAER) elicited by tone bursts or clicks in the presence of high-pass masking noise. Experiment 1 used 1000- and 4000-Hz, 60-dB nHL tone bursts in the presence of broadband noise. With increasing noise level, wave V latency shift was greater for the 1000-Hz tone bursts, while amplitude decrements were similar for both tone-burst frequencies. Experiment 2 varied high-pass masker cutoff frequency and the level of subtotal masking in the presence of 50-dB nHL clicks. The effects of subtotal masking on wave V (increase in latency and decrease in amplitude) increased with increasing derived-band frequency. Experiment 3 covaried high-pass masker cutoff frequency and subtotal masking level for 1000- and 4000-Hz tone-burst stimuli. The effect of subtotal masking on wave V latency was reduced for both tone-burst frequencies when the response-generating region of the cochlear partition was limited by high-pass maskers. The results of these three experiments suggest that most of the wave V latency shift associated with increasing levels of broadband noise is mediated by a place mechanism when the stimulus is a moderate intensity (60 dB nHL), low-frequency (1000 Hz) tone burst. However, the interpretation of the latency shifts produced by broadband noise for 4000-Hz tone-burst stimuli is made more complex by multiple technical factors discussed herein.