Showing papers on "Noise published in 1989"

Headphone simulation of free-field listening. II: Psychophysical validation

Abstract: Listeners reported the apparent spatial positions of wideband noise bursts that were presented either by loudspeakers in free field or by headphones. The headphone stimuli were digitally processed with the aim of duplicating, at a listener’s eardrums, the waveforms that were produced by the free‐field stimuli. The processing algorithms were based on each subject’s free‐field‐to‐eardrum transfer functions that had been measured at 144 free‐field source locations. The headphone stimuli were localized by eight subjects in virtually the same positions as the corresponding free‐field stimuli. However, with headphone stimuli, there were more front–back confusions, and source elevation seemed slightly less well defined. One subject’s difficulty with elevation judgments, which was observed both with free‐field and with headphone stimuli, was traced to distorted features of the free‐field‐to‐eardrum transfer function.

Noise in nonlinear dynamical systems

Abstract: Noise is commonly regarded as having a destructive but relatively innocuous effect, blurring our view of a system but having no effect on the underlying processes involved. In this paper we show, using examples from stochastic nonlinear dynamics, that these intuitive ideas about noise can be very misleading. For example, an effect known as stochastic resonance means that the addition of extra noise to a system can actually improve the signal-to-noise ratio.

Noise-immune phase unwrapping algorithm

Abstract: A new phase unwrapping algorithm is proposed which combines noise immunity with computational efficiency. It is based on the requirement that the unwrapped map should be independent of the route by which unwrapping takes place.

Noise in nonlinear dynamical systems: Noise-induced transitions

Abstract: Will reading habit influence your life? Many say yes. Reading noise induced transitions is a good habit; you can develop this habit to be such interesting way. Yeah, reading habit will not only make you have any favourite activity. It will be one of guidance of your life. When reading has become a habit, you will not make it as disturbing activities or as boring activity. You can gain many benefits and importances of reading.

On reliable curvature estimation

Abstract: An empirical study of the accuracy of five different curvature estimation techniques, using synthetic range images and images obtained from three range sensors, is presented. The results obtained highlight the problems inherent in accurate estimation of curvatures, which are second-order quantities, and thus highly sensitive to noise contamination. The numerical curvature estimation methods are found to perform about as accurately as the analytic techniques, although ensemble estimates of overall surface curvature such as averages are unreliable unless trimmed estimates are used. The median proved to be the best estimator of location. As an exception, it is shown theoretically that zero curvature can be fairly reliably detected, with appropriate selection of threshold values. >

Noise and vibration of electrical machines

Abstract: A. Generation and Elimination of Noise and Vibration. 1. Basic acoustic terms. 2. Generation process of noise and vibration in electrical machines. 3. Electromagnetic noise and causes of vibration. 4. Vibration of rotating electrical machines. 5. Generation of airborne noise in electrical machines. 6. The effect of changes in running condition on the noise of rotating electrical machines. 7. Design considerations to reduce noise and vibration of electromagnetic origin. 8. Mechanical noise and vibrations. 9. Noises of aerodynamic origin. 10. Secondary noise reducing measures. B. Experimental Investigation of Noise and Vibration Phenomena. 11. Measuring noise and vibration phenomena. 12. Measuring the steady-state vibrations of electrical machines. 13. Noise measurements on electrical machines under steady-state operating conditions. 14. Measuring transient noise phenomena. 15. Measuring techniques of transient vibroacoustic signals. 16. Indirect measuring of transient vibroacoustic signals. C. Some Practical Applications of Vibroacoustic Methods in the Testing of Rotating Electrical Machines. 17. Noise and vibration testing in practice. 18. Applying vibration measurement to assessing the technical condition of rotating machines and to scheduling their maintenance. Epilogue with economic considerations. Appendices. References. Subject Index.

Integration of acoustic and visual speech signals using neural networks

Abstract: Results from a series of experiments that use neural networks to process the visual speech signals of a male talker are presented. In these preliminary experiments, the results are limited to static images of vowels. It is demonstrated that these networks are able to extract speech information from the visual images and that this information can be used to improve automatic vowel recognition. The structure of speech and its corresponding acoustic and visual signals are reviewed. The specific data that was used in the experiments along with the network architectures and algorithms are described. The results of integrating the visual and auditory signals for vowel recognition in the presence of acoustic noise are presented. >

Speech recognition using noise-adaptive prototypes

Abstract: A probabilistic mixture mode is described for a frame (the short term spectrum) of speech to be used in speech recognition. Each component of the mixture is regarded as a prototype for the labeling phase of a hidden Markov model based speech recognition system. Since the ambient noise during recognition can differ from that present in the training data, the model is designed for convenient updating in changing noise. Based on the observation that the energy in a frequency band is at any fixed time dominated either by signal energy or by noise energy, the energy is modeled as the larger of the separate energies of signal and noise in the band. Statistical algorithms are given for training this as a hidden variables model. The hidden variables are the prototype identities and the separate signal and noise components. Speech recognition experiments that successfully utilize this model are described. >

A robust orthogonal algorithm for system identification and time-series analysis

Abstract: We describe and illustrate methods for obtaining a parsimonious sinusoidal series representation or model of biological time-series data. The methods are also used to identify nonlinear systems with unknown structure. A key aspect is a rapid search for significant terms to include in the model for the system or the time-series. For example, the methods use fast and robust orthogonal searches for significant frequencies in the time-series, and differ from conventional Fourier series analysis in several important respects. In particular, the frequencies in our resulting sinusoidal series need not be commensurate, nor integral multiples of the fundamental frequency corresponding to the record length. Freed of these restrictions, the methods produce a more economical sinusoidal series representation (than a Fourier series), finding the most significant frequencies first, and automatically determine model order. The methods are also capable of higher resolution than a conventional Fourier series analysis. In addition, the methods can cope with unequally-spaced or missing data, and are applicable to time-series corrupted by noise. Fially, we compare one of our methods with a wellknown technique for resolving sinusoidal signals in noise using published data for the test time-series.

Eye tracking image pickup apparatus for separating noise from feature portions

Abstract: Characteristic features of images of an object eye are extracted to enable non-contact detection of eye movement. Two images of the eye are focused, and a differential image is generated to eliminate background noise and to permit feature extraction to be performed. In one feature of the invention, the illuminating light is polarized for use as a reference and the reflected light is separated to two light paths, each of which is focused to form an image of the object. In one path a polarizing plate blocks the regularly reflected light from the cornea so that only a diffused reflection component of the illuminating light from the other parts of the eye is passed, while in the other path both the regularly and diffusedly reflected light components are passed. A resulting differential image emphasizes the regular reflection component from the cornea relative to the background. In another aspect of the invention, two light sources are placed at different positions relative to the optical axis, to provide bright and dark images of the pupil without otherwise affecting the reflected image. A resulting differential image emphasizes the pupil relative to background noise.

Temporal resolution in children.

Abstract: The auditory temporal resolving power of young children was measured using an adaptive forced-choice psychophysical paradigm that was disguised as a video game. 20 children between 3 and 7 years of age and 5 adults were asked to detect the presence of a temporal gap in a burst of half-octave-band noise at band center frequencies of 400 and 2,000 Hz. The minimum detectable gap (gap threshold) was estimated adaptively in 20-trial runs. The mean gap thresholds in the 400-Hz condition were higher for the younger children than for the adults, with the 3-year-old children producing the highest thresholds. Gap thresholds in the 2,000-Hz condition were generally lower than in the 400-Hz condition and showed a similar age effect. All the individual adaptive runs were "adult-like," suggesting that the children were generally attentive to the task during each run. However, the variability of threshold estimates from run to run was substantial, especially in the 3-5-year-old children. Computer simulations suggested that this large within-subjects variability could have resulted from frequent, momentary lapses of attention, which would lead to "guessing" on a substantial portion of the trials.

Inhibiting the Lombard effect.

Abstract: The Lombard effect is the tendency to increase one’s vocal intensity in noise. The present study reports three experiments that test the robustness of the Lombard effect when speakers are given instructions and training with visual feedback to help suppress it. The Lombard effect was found to be extremely stable and robust. Instructions alone had little influence on the response to the noise among untrained speakers. When visual feedback correlated with vocal intensity was presented, however, subjects could inhibit the Lombard response. Furthermore, the inhibition remained after the visual feedback was removed. The data are interpreted as indicating that the Lombard response is largely automatic and not ordinarily under volitional control. When subjects do learn to suppress the effect, they seem to do so by changing overall vocal level rather than their specific response to the noise.

A family of distortion measures based upon projection operation for robust speech recognition

Abstract: Consideration is given to the formulation of speech similarity measures, a fundamental component in recognizer designs, that are robust to the change of ambient conditions. The authors focus on the speech cepstrum derived from linear prediction coefficients (the LPC cepstrum). By using some common models for noisy speech, they show analytically that additive white noise reduces the norm (length) of the LPC cepstral vectors. Empirical observations on the parameter histograms not only confirm the analytical results through the use of noise models but further reveal that at a given (global) signal-to-noise ratio (SNR), the norm reduction on cepstral vectors with larger norms is generally less than on vectors with smaller norms, and that lower order coefficients are more affected than higher order terms. In addition, it is found that the orientation (or direction) of the cepstral vector is less susceptible to noise perturbation than the vector norm. As a consequence of the above results, a family of distortion measures based on the projection between two cepstral vectors is proposed. The new measures have the same computational efficiency as the band-pass cepstral distortion measure. >

Reverberant overlap‐ and self‐masking in consonant identification

Abstract: Two effects of reverberation on the identification of consonants were evaluated for ten normal‐hearing subjects: (1) the overlap of energy of a preceding consonant on the following consonant, called ‘‘overlap‐masking’’; and (2) the internal temporal smearing of energy within each consonant, called ‘‘self‐masking.’’ The stimuli were eight consonants /p,t,k,f,m,n,l,w/. The consonants were spoken in /s–at/ context (experiment 1) and generated by a speech synthesizer in /s–at/ and /–at/ contexts (experiment 2). In both experiments, identification of consonants was tested in four conditions: (1) quiet, without degradations; (2) with a babble of voices; (3) with noise that was shaped like either natural or synthetic /s/ for the two experiments, respectively; and (4) with room reverberation. The results for the natural and synthetic syllables indicated that the effect of reverberation on identification of consonants following /s/ was not comparable to masking by either the /s/‐spectrum‐shaped noise or the babble. In addition, the results for the synthetic syllables indicated that most of the errors in reverberation for the /s–at/ context were similar to a sum of errors in two conditions: (1) with /s/‐shaped noise causing overlap masking; and (2) with reverberation causing self‐masking within each consonant.

Responsivity Nonuniformity Limited Performance Of Infrared Staring Cameras

Abstract: . The effect of noise, including system noise, background noise, and cell-to-cell nonuniformity (spatial noise), is mathematically treated and experimentally verified for staring-mode infrared cameras. Spatial noise is shown to be dominant in high background environments (3 to 5 Am or 8 to 12 Am imagery at background temperatures greater than 0°C) even after compensation. Camera sensitivity is quantified by a contrast signal-to-noise ratio that includes the effects of system, background, and spatial noise. Past analysis of camera performance has assumed that the cell-to-cell nonuniformity can be completely removed by using nonuniformity correction techniques. We present data showing that neither variations in detector spectral response nor excess low frequency noise can be fully corrected using existing nonuniformity correction techniques. Furthermore, we show that even the small amounts of nonuniformity that persist after the application of correction algorithms will significantly degrade camera performance.

Accuracy improvements in microwave noise parameter measurements

Abstract: Factors contributing to the accuracy of microwave noise parameter measurements are examined theoretically and experimentally. It is shown that for good accuracy the test source impedances need not be grouped around the impedance that produces the minimum noise figure. System calibration and device under test (DUT) S-parameter accuracy are important to the derived noise parameter accuracy, and the use of a vector network analyzer is advantageous. An algorithm is implemented which avoids errors caused by different noise-source 'on' and 'off' impedances. >

Filtering of colored noise for speech enhancement and coding

Abstract: A report is presented on experiments using a colored-noise assumption Kalman filter to enhance speech additively contaminated by colored noise, such as helicopter noise and jeep noise, with a particular application to linear predictive coding (LPC) of noisy speech. The results indicate that the colored-noise Kalman filter provides a significant gain in SNR, a clear improvement in the sound spectrogram, and an audible improvement in output speech quality. The authors demonstrate that such gains are unavailable with white noise assumption Kalman and Wiener filters. The colored-noise prefilter greatly enhances the quality and intelligibility of LPC output speech for noisy inputs. >

Noise Modeling and Estimation of Remotely-Sensed Images

Abstract: A noise model is defined for remotely sensed images, and the noise statistics are estimated by using the means and variances from small (4x4 or 8x8) image blocks. Since most images contain many small but homogeneous areas, a scatter plot of variance vs (mean)' reveals characteristics of the noise. The Hough transform is then applied to the scatter plot to detect a straight line through the maj or cluster of data points. This defines the image noise statistics. Images from SAR, Landsat TM, and passive microwave Sensors are used for illustration.

Spatially mediated release from auditory masking in an anuran amphibian

Abstract: Summary. 1. The acoustic environment in which many species of frogs must communicate is characterized by high levels of background noise. Because the anuran auditory system is directionally sensitive, spatial cues should be useful in enhancing the ability of these animals to detect and localize calling conspecifics under such conditions. 2. We presented female green treefrogs, Hyla cinerea, with synthetic conspecific advertisement and aggressive calls in the presence of background broadband noise to assess the importance of directional information in signal detection, discrimination and localization. 3. We found that angular separation of call and noise sources facilitated a release from masking; females which failed to orient towards and approach speakers broadcasting calls positioned adjacent to a noise source did so when the noise sources were separated from the speakers by 45 ~ or 90 ~ . We estimate the improvement in signal-to-noise ratio with separation to be 3 dB or less. This increase was insufficient to facilitate discrimination between advertisement and aggressive calls.

Modeling of sound propagation in fitted workshops using ray tracing

Abstract: This article describes the rayscat computer model, for prediction of noise levels in empty or fitted rooms. The model is based on a ray‐tracing technique and takes into account both the real geometry of the room and areas with different fittings (furniture, machines, storage, etc.). Experimental results obtained in a test room are presented, demonstrating the influence of the fitting distribution on noise levels. Finally, the experimental results are compared with those obtained by numerical simulation using the rayscat model. Predicted values agree closely with measured ones.

Computer-aided noise analysis of MESFET and HEMT mixers

Abstract: A numerical approach to the noise analysis of MESFET and HEMT mixers of arbitrary topology is discussed. A qualitative picture of the complex physical mechanisms responsible for the generation of the intermediate frequency (IF) noise is outlined, and the corresponding computational algorithms are presented. The derivation of a noisy nonlinear model for the microwave FET is addressed, and it is shown that a satisfactory solution to this problem can be obtained by combining a conventional time-domain model with standard noise information. The method has been implemented in a computer program designed to work in conjunction with an existing general-purpose harmonic-balance simulator. An application is described in detail to demonstrate the excellent performance of this software tool. >

Acoustic analysis of gradient-coil noise in MR imaging.

Abstract: A survey was conducted of acoustic noise levels in magnetic resonance (MR) imaging systems. Static magnetic flux and radio-frequency pulses did not affect the function of shielded sound-pressure detection equipment. Noise levels were measured at bore isocenter during a variety of imaging sequences in six MR imaging systems with magnetic fields of 0.35-1.5 T. Measured noise ranged from 82 to 93 dB on the A-weighted scale and from 84 to 103 dB on the linear scale. Noise levels increased during sequences employing thinner section thickness and shorter repetition and echo times and were independent of field strength. Gradient-coil noise in MR imaging is an annoyance but is well within safety guidelines.

Localization and noise in edge detection

Abstract: Two aspects of edge detection are analyzed, namely accuracy of localization and sensitivity to noise. The detection of corners and trihedral vertices is analyzed for gradient schemes and zero-crossing schemes. It is shown that neither scheme correctly detects corners of trihedral vertices, but that the gradient schemes are less sensitive to noise. A simple but important conclusion is that the noise present in digital images of typical indoor scenes is small and the signal-to-noise ratio is high. The noise present in digital images is so small as to make the performances of a variety of filters almost indistinguishable. As a consequence small filters can be used and the exact shape of the filter is not critical. >