Showing papers on "Noise (signal processing) published in 1991"

Filtering of colored noise for speech enhancement and coding

Abstract: Scalar and vector Kalman filters are implemented for filtering speech contaminated by additive white noise or colored noise, and an iterative signal and parameter estimator which can be used for both noise types is presented. Particular emphasis is placed on the removal of colored noise, such as helicopter noise, by using state-of-the-art colored-noise-assumption Kalman filters. The results indicate that the colored noise Kalman filters provide a significant gain in signal-to-noise ratio (SNR), a visible improvement in the sound spectrogram, and an audible improvement in output speech quality, none of which are available with white-noise-assumption Kalman and Wiener filters. When the filter is used as a prefilter for linear predictive coding, the coded output speech quality and intelligibility are enhanced in comparison to direct coding of the noisy speech. >

Spectrally optimal sampling for distribution ray tracing

Abstract: Nonuniform sampling of images is a useful technique in computer graphics, because a properly designed pattern of samples can make aliasing take the form of high-frequency random noise. In this paper, the technique of nonuniform sampling is extended from two dimensions to include the extra parameter dimensions of distribution ray tracing. A condition for optimality is suggested, and algorithms for approximating optimal sampling are developed. The technique is demonstrated at low sampling densities, so the characteristics of aliasing noise are clearly visible. At supersampling rates, this technique should move noise into frequencies above the passband of the pixel-reconstruction filter.

Cumulant-based approach to harmonic retrieval and related problems

Abstract: A frequently encountered problem in signal processing is that of estimating the frequencies and amplitudes of harmonics observed in additive colored Gaussian noise. In practice, the observed signals are contaminated with spatially and temporally colored noise of unknown power spectral density. A cumulant-based approach to these problems is proposed. The cumulants of complex processes are defined, and it is shown that specific 1-D slices of the fourth-order cumulant of the noisy signal for the direction of arrival (DOA) and retrieval of harmonics in noise (RHN) problems are identical to the autocorrelation of a related noiseless signal. Hence correlation-based high-resolution methods may be used with fourth-order cumulants as well. The effectiveness of the proposed methods is demonstrated through standard simulation examples. >

Method and apparatus for cancelling spread-spectrum noise

Abstract: A spread-spectrum noise canceller is provided for cancelling user code noise from a spread-spectrum communication channel. The spread-spectrum noise canceller includes a receiver for receiving a spread-spectrum signal (114, 202 or 302) including a first (108, 204 or 304) and at least a second (110, 206 or 306) signal as well as a noise canceller operatively coupled to the receiver for reducing spread-spectrum noise in the first received signal (108, 204 or 304) by substantially processing the at least second received signal out of the received spread-spectrum signal (114, 202 or 302). In addition, a method is provided which cancels user code noise from a spread-spectrum communication channel. The method includes receiving a spread-spectrum signal (114, 202 or 302) including a first (108, 204 or 304) and at least a second (110, 206 or 306) signal and subsequently reducing spread-spectrum noise in the first received signal (108, 204 or 304) by substantially processing the at least second received signal 110, 206 or 306) out of the received spread-spectrum signal (114, 202 or 302).

Noise squelch circuit with adaptive noise shaping

Abstract: A noise squelch circuit for a radio receiver (100) includes an adaptive filter (204) for shaping frequency characteristics of a demodulator out put (115) according to factors which effects squelch sensitivity. Such factors may include channel spacing of the receiver, received signal strength level, received signal deviation, and SINAD. The adaptive filter (204) comprises a switched capacitor filter, the response of which may be controlled by a control signal (212) according to one or more of such factors.

A new method of channel identification

Abstract: A method of channel identification is proposed that exploits the spectral correlation properties of pulse- and carrier-modulated signals to identify channels in the presence of arbitrary noise and nearly arbitrary interference Although a pilot or training signal is required, no replica of the transmitted pilot/training signal is needed at the receiver The price paid for this simplicity and the tolerance to extreme channel corruption from noise or interference is that the method is slow That is, relatively long averaging times are needed for measurement of the spectral correlation of the received signal >

Speech signal coding/decoding system based on the type of speech signal

Abstract: An input speech signal is encoded by an adaptive quantizer which quantizes the predicted residual signal between the digital input speech signal, and prediction signals provided by predictors and a shaped quantization noise provided by a noise shaping filter. An inverse quantizer, to which the encoded speech signal is supplied, is provided for noise shaping and local decoding. A noise shaping filter makes the spectrum of the quantization noise similar to that of the original digital input speech signal by using the shaping factors. The shaping factors are changed depending upon the prediction gain (ex. ratio of input speech signal to predicted residual signal or the prediction coefficients). On a decoding side of the system there are an inverse quantizer, predictors, and a post noise shaping filter. The shaping factors for the post noise shaping filter are similarly changed depending upon the prediction gain.

Noise reduction system

Abstract: A technique is provided to remove noise from images and to enhance their visual appearance through the utilization of a technique which converts an image into a set of coefficients in a multi-scale image decomposition process, followed by modification of each coefficient based on its value and the value of coefficients of related orientation, position, or scale, which is in turn followed by a reconstruction or synthesis process to generate the enhanced image. Also contributing to the improved enhancement is a set of orientation tuned filters of a specialized design to permit steering, with the analysis and synthesis filters also having a self-inverting characteristic. Additionally, steerable pyramid architecture is used for image enhancement for the first time, with the steering being provided by the above orientation tuned filters. The utilization of related coefficients permits coefficient modification with multipliers derived through a statistical or neural-network analysis of coefficients derived through the utilization of clean and degraded images, with the modifiers corresponding to vectors which result in translating the degraded image coefficients into clean image coefficients, in essence by cancelling those portions of a coefficient due to noise. Further improvements include an overlay of classical coring on single coefficients. Thus, the subject technique provides improved image enhancement through the use of a multi-band or scale-oriented analysis and synthesis transform having improved coefficient modification, good orientation tuning, improved bandpass characteristics, and good spatial localization.

Method and apparatus for continuously measuring volumetric flow

Abstract: Method and apparatus for adapting the volumetric flow rate measurement system thaught by Yelderman in U.S. Patent No. 4,507,974 to clinical environments by reducing the effects of physiological noise. Signal processing techniques are used to characterize the background noise power spectrum of the system under test so that the effect of noise aberrations on the measured data may be eliminated and so that the predominant periodicities of the background noise spectra may be avoided. The invention further cross-correlates the input data of the system with the corresponding output data of the system to determine weighting values for each input frequency so that data collected at noisy frequencies is discounted. Low frequency noise or drift is also removed from the output signal by fitting the average of the output data to a quadratic function which is then subtracted from the original output signal, point by point. Finally, the processed data is fit to a lagged normal distribution curve in the frequency domain to solve for the parameters necessary to mathematically model the transfer function of the system. Given the input to the system as well as the frequency domain transfer function and noise data of the system, the volumetric flow of the system then may be determined for virtually any input even in very noisy environments.

Zero intermediate frequency noise blanker

Abstract: An essentially zero intermediate frequency receiver (100) for recovering an information signal from a received signal (110), which includes means for blanking noise signals which may otherwise deteriorate performance, comprises a receiver (10) for recovering the information signal and a noise blanker (28). The receiver (28) comprises at least one conversion mixer (32B) for operating on the received signal (110) to provide an essentially baseband signal (125B), at least one delay filter (40B) coupled to the conversion mixer (32B) for producing a delayed essentially baseband signal, and at least one blanker switch (S1-S4) for operating on the delayed essentially baseband signal to temporarily prevent recovery of the information signal in response to a control signal (58). To provide the control signal (58), the noise blanker (28) is coupled to the receiver (10) for operating on either the essentially baseband signal (125B) or the received signal (110) as a noise blanker input signal.

Active noise controller

Abstract: PURPOSE:To adequately control a noise based upon any signal component and to reduce the size of the device by selecting and controlling a signal component which has high autocorrelativeness or signal component having no correlation as a component which is dominant to the noise even if the noise is based upon both the components. CONSTITUTION:A noise generation state detecting means 5 detects a signal regarding the noise generation states of plural noise sources and signal component selecting means 41, 43, and 45 select the signal component with high autocorrelativeness or the signal component having no correlation as the component which is dominant to the noise from the output signal of the noise generation state detecting means 5. An adaptive digital filter 13 filters the output signal of the signal component selecting means 45 according to a specific filter coefficient and outputs a signal for driving a control sound source. At this time, an adaptive controller 16 sequentially updates the filter coefficient according to the output signals of residual noise detecting means 8a-8h and the output signal of the signal component selecting means 45 so that the output signals of the residual noise detecting means 8a-8h are reduced.

Noise suppression system

Abstract: A noise cancellation system, comprising a symmetrical assembly (24, 26) of microphone inputs is disclosed. A controller (46) receives the output of the microphone assembly (49, 50) and generates an electrical cancellation signal having a polarity opposite the polarity of a portion of a noise to be cancelled and a magnitude equal to the magnitude of the portion of the noise to be cancelled. An actuator (16, 18) receives the electrical cancellation signal and outputs an audio cancellation signal.

Speech enhancement based conceptually on auditory evidence

Abstract: A new idea, enhancing speech based on auditory evidence, is explored for the problem of enhancing speech degraded by stationary and nonstationary additive white noise. Distinguishing different objectives for heavy and light noise interference, two related algorithms are developed. For speech degraded by heavy noise, the improvement in signal-to-noise ratio (SNR) is as high as 12 dB; for lightly noisy speech, the improvement is modest and decreases as the SNR of the noisy speech increases. Quantizing noise is used to assess the capacity for reducing nonstationary noise using these algorithms; a significant reduction of such noise and an improvement in speech quality are achieved. The advantages of the proposed algorithms for speech enhancement include no need for prior knowledge of the noise and only a modest computational requirement. >

Colorimetric calibration for scanners and media

Abstract: Colorimetric calibration techniques were studied for scanners that do not adhere to colorimetric requirements (the Luther condition) from the aspects of accuracy and signal noise. A newly developed calibration technique was compared with conventional polynomial regression models and was found to be more accurate. Computer simulations were performed to find the relationship between scanner responsivities and resultant chroma noise. The scanner matching the Luther condition exhibits larger chroma noise than a scanner having three separated responsivities due to the overlap among responsivities of each channel.

EMC: Electromagnetic Theory to Practical Design

Abstract: Probability Noise and Random Processes The Sampling Theorem, Oversampling and Discrete-Time Signals Signal Detection in Gaussian and Shot Noise Coherent and Non-Coherent Integration Estimation of Range, Position and Acceleration of a Target and Prediction of Target Position as a Function of Tracking Time Waveform Analysis and Ambiguity Large Time-Bandwith Signals.

Adaptive processing techniques based on hidden Markov models for characterizing very small channel currents buried in noise and deterministic interferences.

Abstract: Techniques for characterizing very small single-channel currents buried in background noise are described and tested on simulated data to give confidence when applied to real data. Single channel currents are represented as a discrete-time, finite-state, homogeneous, Markov process, and the noise that obscures the signal is assumed to be white and Gaussian. The various signal model parameters, such as the Markov state levels and transition probabilities, are unknown. In addition to white Gaussian noise, the signal can be corrupted by deterministic interferences of known form but unknown parameters, such as the sinusoidal disturbance stemming from AC interference and a drift of the base line owing to a slow development of liquid-junction potentials. To characterize the signal buried in such stochastic and deterministic interferences, the problem is first formulated in the framework of a Hidden Markov Model and then the Expectation Maximization algorithm is applied to obtain the maximum likelihood estimates of the model parameters (state levels, transition probabilities), signals, and the parameters of the deterministic disturbances. Using fictitious channel currents embedded in the idealized noise, we first show that the signal processing technique is capable of characterizing the signal characteristics quite accurately even when the amplitude of currents is as small as 5-10 fA. The statistics of the signal estimated from the processing technique include the amplitude, mean open and closed duration, open-time and closed-time histograms, probability of dwell-time and the transition probability matrix. With a periodic interference composed, for example, of 50 Hz and 100 Hz components, or a linear drift of the baseline added to the segment containing channel currents and white noise, the parameters of the deterministic interference, such as the amplitude and phase of the sinusoidal wave, or the rate of linear drift, as well as all the relevant statistics of the signal, are accurately estimated with the algorithm we propose. Also, if the frequencies of the periodic interference are unknown, they can be accurately estimated. Finally, we provide a technique by which channel currents originating from the sum of two or more independent single channels are decomposed so that each process can be separately characterized. This process is also formulated as a Hidden Markov Model problem and solved by applying the Expectation Maximization algorithm. The scheme relies on the fact that the transition matrix of the summed Markov process can be construed as a tensor product of the transition matrices of individual processes.

Wireless remote control apparatus for camera

Abstract: A wireless camera remote control apparatus comprises a transmitter unit for transmitting an activating pulse and a plurality of code pulse signals corresponding to given operations of the camera; and a receiver unit responsive to a code defined by the plurality of code pulses for causing the camera to execute a given operation. The wireless camera remote control apparatus has an immunity to disturbance noise and a reduced power consumption.

Optical information recording/reproducing apparatus

Abstract: There is provided an optical information recording/reproducing apparatus including a unit for detecting the focus error signal from the reflected light flux from a recording layer of an optical recording medium, and a unit for focusing the light flux on the recording layer of the optical disk on the basis of the focus error signal. In the case of detecting the focus error signal, the light flux of the effective numeric aperture NAeff<1 due to an objective lens and the SIL within a pupil is obtained by a splitting device as the focus error signal, whereby it is possible to suppress the reflected light from the bottom surface of the SIL from being mixed into the focus error signal as a noise.

Apparatus and method for equalizing a corrupted signal in a receiver

Abstract: An equalization system for equalizing a corrupted signal is disclosed. The equalization system includes a complex matched filter (400) and a maximum likelihood sequence estimator (MLSE) (405) for removing the effects of phase shift, amplitude variations, intersymbol interference, etc. resulting from multi-pathing and noise contributed by the receiver front end. The system estimates a correlation signal C(t) (505) and synchronizes C(t) 505 to maximize its energy as seen on the taps of the complex matched filter (400). Taps having amplitude coefficients below a predetermined threshold are set to zero to produce a modified CIR estimate. The modified CIR estimate which has had the effects of noise virtually eliminated, is then used to construct the complex matched filter (400) and is also used as input to the MLSE (405) to produce a better equalized data signal.

Read-out of photodiodes using sigma-delta oversampled analog-to-digital converters.

Abstract: Sigma-delta analog-to-digital conversion is used in sensing apparatus that generates a digital signal descriptive of light energy received by a photosensor, such as one of a plurality of photosensors that together receive various elements of a radiant-energy image. A preamplifier generates an analog output signal responsive to the photocurrent of the photosensor, which analog output signal is undesirably accompanied by wideband noise. The analog output signal is supplied to a sigma-delta analog-to-digital converter, the decimation filter of which not only suppresses in the digital signal a component arising from the quantization noise from the sigma-delta modulator portion of the analog-to-digital converter, but also suppresses a component arising from remnant wideband noise from the preamplifier.

Notch filter noise rejection system in a cardiac control device

Abstract: A physiological event signal sensing system in a cardiac control or monitoring device for detecting spontaneous cardiac electrical events which may be obscured by continuous or burst EMI line frequency noise. The noise rejecting sensing system of this invention senses and samples cardiac signals which may include a noise component which is produced by power line interference in addition to a physiological signal component. The sampling frequency is selected to be an integer multiple of at least one common power line frequency. The system notch filters the cardiac signal to remove line frequency components, using either or both lowpass and highpass notch filtering coefficients, then limits the filtered output to the amplitude of the corresponding filter input to remove filter output signals caused by the sudden termination of line frequency noise which is characteristic of burst noise.

Rapid programmable 300 ps optical delay scanner and signal-averaging system for ultrafast measurements

Abstract: A device is presented that sweeps out programmable optical delays of 300 ps (or less) at 30 Hz, with shorter‐delay scans possible at much higher rates. It is compact, vibration‐free, linear to within 0.02%, and has a position repeatability of 1 part in 105. With this scanner and a PC‐based signal‐averaging data acquisition system, ultrafast autocorrelation measurements with very high signal/noise are demonstrated in both the fs and ps domains.

A radially-Gaussian, signal-dependent time-frequency representation

Abstract: An optimization formulation for designing signal-dependent kernels that are based on radially Gaussian functions is presented. The method is based on optimality criteria and is not ad hoc. The procedure is automatic. The optimization criteria are formulated so that the resulting time-frequency distribution (TFD) is insensitive to the time scale and orientation of the signal in time-frequency. Examples demonstrate that the optimal-kernel TFD offers excellent performance for a larger class of signals than any current fixed-kernel representation. The technique performs well in the presence of substantial additive noise, which suggests that it may prove useful for automatic detection of unknown signals in noise. The cost of this technique is only a few times greater than that of the fixed-kernel methods and the 1/0 optimal kernel method. >

Microscopic study of 1/ f noise in metal nanobridges

Abstract: Extensive studies of 1/f noise and its microscopic constituents have been conducted in clean metal nanobridges 3--40 nm wide. The resistance noise results from the fluctuation of metastable defects between discrete configurations; at low temperatures, activation energies, scattering cross-section changes, and attempt times are measured. Interactions between defects dominate the high-temperature noise signal, and are, in fact, required to produce a 1/f noise signal. The measured interaction strength is too large to be explained by a simple model of fluctuating elastic dipoles interacting through the lattice strain field. The analysis suggests that collective reconfigurations of regions of a ``defect glass'' are responsible both for the discrete fluctuations and the strong interaction energy. Implications for more disordered systems are discussed.

Condensed oximeter system with noise reduction software

Abstract: A compact pulse oximetry system which separates the combined signal into its respective AC and DC components. By separating the signal into AC and DC components, a smaller order bit A/D converter may be used while still maintaining signal accuracy. Instead of using the combined signal to calculate the oxygen saturation content, the system microprocessor computes the Ratio of Ratios using the derivative of the separated AC component of the diffused signal to calculate the oxygen saturation of the measured fluid. To calculate the Ratio of Ratios, a ratio of the derivative value of the separated AC component is used. Instead of taking a single sample between the peak and valley of the signal, the oximeter system samples each value. To decrease the effect of system noise, a linear regression is performed over each sample.

Digital automatic gain control

Abstract: There is provided a mechanism for Automatic Gain Control in a receiver. It comprises: determining, within a certain dynamic range, the difference in power between the desired signal and a signal received, and providing open loop gain control for the signal in response to the differential so determined, scaled by the receiver's gain characteristics, such that the signal is positioned within dynamic range so as to reduce saturation and noise.