Showing papers on "Center frequency published in 1983"

Suggested formulae for calculating auditory‐filter bandwidths and excitation patterns

Abstract: Recent estimates of auditory‐filter shape are used to derive a simple formula relating the equivalent rectangular bandwidth (ERB) of the auditory filter to center frequency. The value of the auditory‐filter bandwidth continues to decrease as center frequency decreases below 500 Hz. A formula is also given relating ERB‐rate to frequency. Finally, a method is described for calculating excitation patterns from filter shapes.

Gap detection as a function of frequency, bandwidth, and level.

Abstract: The threshold for detection of a temporal gap in a noiseband was measured. A notched noise masker was used to restrict listening to a limited spectral region. Threshold was measured as a function of center frequency, bandwidth, and level. For a signal bandwidth of one‐half the center frequency, the gap threshold decreased from 22.5 ms for a center frequency of 0.2 kHz to 3.2 ms at 8.0 kHz: a wideband condition provided an estimate of 2.3 ms, a value in agreement with previously published estimates. Bandwidth manipulation showed that the variation with frequency was not due to changes in absolute bandwidth alone. The effect of changes in level was determined at three frequencies, 0.4, 1.0, and 6.5 kHz, using a signal bandwidth of half the center frequency. At all frequencies gap threshold decreased as the signal spectrum level was raised from 10 to 25 dB, but a further increase to 40 dB showed no additional improvement. At frequencies up to about 1.0 kHz, the variation of gap threshold with frequency matches well the reciprocal of the bandwidth of the auditory filter, as determined from masking experiments using a notched‐noise masker. This suggests that the temporal response of the auditory filter may limit gap detection at low frequencies.

Temporal gap detection in noise as a function of frequency, bandwidth, and level

Abstract: Temporal gap resolution is measured with Bekesy tracking procedure and filtered noise stimuli in the frequency range below 6000 Hz. Stimulus parameters include high‐pass and low‐pass cutoff frequency, band center frequency, bandwidth in a 2‐oct range, and signal level in the low‐to‐moderate intensity range. The pattern of results indicates that gap resolution improves with an increase in stimulus frequency in a manner that can be described by a linear function with a slope of about 2 ms/oct. This relationship applies to signal levels greater than 25–30 dB SL. A linear trend also describes gap threshold as a function of the empirical critical bandwidth within the same frequency range. Implications of the results for simple functional models of temporal processing are examined.

System for digital multiband filtering

Abstract: A digital filter system in which the frequency spectrum of an input signal is divided into M consecutive subbands. Each subband is generated by multiplying the impulse reponse of a low pass filter by a sinusoid (sine or cosine) whose frequency is equal to the center frequency of its respective subband. The sinusoids of adjacent bands are phase shifted by 90° relative to each other to establish a condition enabling aliasing components to be cancelled when the subbands are recombined.

Crossed beam high frequency anti-theft system

Abstract: An article surveillance system employs a label or tag containing a non-linear impedance element, such as a semiconductor diode, connected to a metal antenna loop configured to pick up two distinct radio frequency transmissions displaced on either side of a selected center frequency. The non-linear impedance element connects opposing sides of a closed loop section at one end of the antenna to form a tuned tank circuit having a resonant frequency twice that of the selected center frequency. A first transmitter generates a tone modulated radio frequency displaced on one side of the center frequency, and a second transmitter generates a continuous wave radio frequency displaced from the center frequency on the other side. Both transmitter signals are fed separately to respective radiating antennae located adjacent to a surveillance area. The antennae are chosen to produce circularly polarized transmission of both frequencies within the surveillance area. The two different frequencies picked up by the transponder antenna are mixed by the non-linear impedance causing the tank circuit to resonate at a single higher frequency equal to their sum, which is double the center frequency; that resonant frequency is reradiated to be picked up by a receiver antenna or antennae suitably placed with respect to the surveillance zone to be detected by a very narrow band receiver responsive to the sum frequency. The modulating tone signal is derived from the received signal to produce a gradually increasing charge that is compared against a preselected threshold level to trigger an alarm for a fixed interval only when the detected signal is of a sufficient strength and duration.

Conversion of acoustic signals into visual signals

Abstract: For displaying spoken words as color pictures on a screen, each audio frequency, ie each acoustic sound, is assigned a respective color hue and each audio frequency spectrum a respective color mixture, by conducting acoustic signals through a three-channel triangular filter, each channel having a different central frequency, and controlling the intensity of a respective electron beam of a color television monitor as a function of a respective filter channel output

Method of fitting hearing prosthesis to a patient having impaired hearing

Abstract: Disclosed is a process of fitting a hearing prosthesis to a deaf or severely hearing impaired patient. The prosthesis is connected to the patient, and a signal is then applied to the prosthesis across an audioband. The frequency response of the prosthesis is adjusted so that the patient detects a desired response to the signal. In one application the prosthesis may include a sound processor driving a transmitter, a transcutaneous receiver, and an implanted electrode. A constant amplitude signal is applied to the sound processor, and the frequency response of the sound processor is adjusted so that the patient detects a generally uniform response to the signal. Other signals can be applied, such as bursts of a sine wave or other periodic wave, and band-filtered noise can be employed with the band center frequency being swept either step-wise or continuously. The transmitter and receiver are first adjusted for normal operating coupling and then a constant amplitude continuous sinusoidal signal, for example, is applied. In a multiple channel system, the signal is applied sequentially to each channel. For each channel, the signal is varied in discrete frequency steps across an audio band, and the frequency response of the transmitter is adjusted so that the patient detects a generally uniform response. The dynamic range is identified at each such frequency step between a threshold level and a discomfort level to establish desired aided thresholds and discomfort levels.

Prosthetic device for optimizing speech understanding through adjustable frequency spectrum responses

Abstract: Electronic circuitry for providing compensatory amplification to restore speech clarity for aurally handicapped persons comprising multiple active filters in a lowpass, bandpass, highpass (LP/BP/HP) configuration which provides composite filter responses applicable to infinite combinations of hearing deficiencies through multiple adjustments of filter gains, BP center frequency, LP/HP break frequencies, and BP filter "Q". This action achieves a precise corrective hearing response in wearable behind-the-ear and in-the-ear hearing aids.

Use of pseudorandom noise in studies of frequency selectivity: The periphery of the auditory system

Abstract: Frequency selectivity of single auditory nerve fibers in the rat was studied using pseudorandom noise based on ternary m-sequences as the stimulus, and the results were compared to those of earlier studies in which noise based on binary m-sequences was used. Pseudorandom noise based on ternary m-sequences has fewer anomalies than noise based on binary m-sequences. Detailed tests using linear and nonlinear filters showed that the present method provides acurate measures of bandwidth and center frequency. Period histograms of the response, locked to the periodicity of the noise, were cross-correlated with one period of the noise to obtain estimates of the impulse response function of the peripheral auditory system. Fourier transforms of these cross-correlograms were used as estimates of the filter function of single auditory nerve fibers. The results obtained using ternary noise were not different from previous results showing a downward shift in center frequency and increase in bandwidth with increasing stimulus intensity for fibers with center frequencies between 1000 and 5000 Hz. The difference between spectral selectivity based on phase-locked responses and that based on discharge rate is discussed.

Frequency modulation-polarization spectroscopy method and device for detecting spectral features

Abstract: A method and device for detecting dichroic and/or birefringent narrow spectral features in a sample is described The method includes the steps of providing a beam of light having an optical frequency bandwidth which is narrow compared to the width of the narrow spectral feature and having a center frequency ωc which lies near the narrow spectral feature, polarization phase modulating a beam of light with a single RF frequency to provide a pure FM spectrum having upper and lower sidebands in which either the carrier and sidebands have been polarized with respect to one another, exposing the sample containing the narrow spectral feature to the polarized modulated light so that the FM sidebands probe the narrow spectral feature, polarization analyzing and then photodetecting the light emerging from the sample to detect a RF beat at the specific RF frequency used for the polarization phase modulation, and electronically monitoring the amplitude of the RF beat signal to indicate the strength of the narrow spectral feature The device includes a polarization phase modulator and a polarization analyzer positioned on opposite sides of the sample In a preferred embodiment the polarization phase modulator produces a frequency modulated optical spectrum with the sidebands polarized precisely orthogonal to the carrier

Photoinduced grating filters in GeO2 thin-film waveguides.

Abstract: Narrowband grating filters were fabricated in GeO2 thin-film optical waveguides by optically induced changes in the refractive index. Intense counterpropagating laser beams inside the waveguide resulted in distributed feedback reflectors having a peak efficiency of 40%. The spectral response of the filters was measured by thermal tuning of the center frequency and agreed with the results of a coupled-mode analysis. The filter bandwidths were <0.01 nm.

Pitch and spectral estimation of speech based on auditory synchrony model

Abstract: This paper describes a system for processing sonorant regions of speech, motivated by knowledge of the human auditory system. The spectral representation is intended to reflect a proposed model for human auditory processing of speech, which takes advantage of synchrony in the nerve firing patterns to enhance formant peaks. The auditory model is also applied to pitch extraction, and thus a temporal pitch processor is envisioned. The spectrum is derived from the outputs of a set of linear filters with critical bandwidths. Saturation and adaptation are incorporated for each filter independently. Each “spectral” coefficient is determined by weighting the amplitude response at that frequency (corresponding to mean firing rate) by a measure of synchrony to the center frequency of the filter. Pitch is derived from a waveform generated by adding the (weighted) rectified filter outputs across the frequency dimension. The system performance is evaluated by processing of a variety of signals, including natural and synthetic speech, and results are compared with other processing methods and with known psychoacoustical data from these types of stimuli. [Work supported in part by NINCDS and the System Development Foundation.]

A Broadband Submillimeter Wave Spectrometer System with On-Line Microcomputer Data Analysis

Abstract: A submillimeter wave spectrometer operating in the frequency range 100 to 800 GHz has been constructed for the study of transient molecules in the gas phase. The instrument employs harmonic generation of millimeter wave frequencies and a He-cooled InSb photoconducting detector. A high degree of flexibility is achieved using an exchangeable free-space Pyrex absorption cell and a microcomputer for on-line data analysis. The spectrometer can be operated in a free-running video mode together with a fast signal averager or phase-locked to a microwave reference with source modulation. It is shown that the reproducibility of line center frequency measurements up to 600 GHz is ± 10 kHz. Transitions with absorption coefficients of at least 3 · 10−8 cm−1 can be detected in the range from 150 to 250 GHz. Ground state rotational transitions of OCS between 200 and 690 GHz are reported and analysed together with previous data.

Magnetic bearing control device

Abstract: PURPOSE:To prevent the dynamic stiffness of revolving shaft in its proper frequency from reducing by providing the band-pass filter having the center frequency close to the proper frequency of revolving shaft, the band-elimination filter having less center frequency than it and the phase lead circuit in series connection. CONSTITUTION:An adding machine 4 to compose the detection signal from a sensor 2 and the standard position from a standard shaft position indicator 3 outputs a deflection signal obtained by subtracting the detection signal from the standard position. This deflection signal is transmitted to an adding machine 15 through the band-pass filter 11 having the center frequency close to the proper frequency of revolving shaft, the band-elimination filter 12 having a less center frequency than it, and a serial circuit consisting of a phase lead circuit 13 to conpensate the phase lag caused by the filters 11, 12. The current from electromagnet 9 to coil 10 is controlled by the adding machine 15 after the output of integrating circuit 16 is subtracted from the output signal of serial circuit 14.

Extended bandwidth switched element phase shifter having reduced phase error over bandwidth

Abstract: Switched line phase shifters are provided with an increased operating frequency range for a given level of phase setting accuracy by providing increased-resolution phase shifters and by translating phase commands in accordance with the center frequency of the signal to be phase shifted.

Visual sound device

Abstract: This invention describes a visual sound device for use in the visual interpretation of a received electrical sound signal, which has an electro visual means that responds visually in amplitude to the amplitude variations of the intelligence contained within a band of frequencies contained within the frequency spectrum of a received electrical sound signal The device consists of at least one channel, which has a filter that passes the intelligence contained within the band pass of the filter and an amplifier which amplifies the intelligence, a rectifier for rectifying the amplified intelligence, and, a power amplifier which amplifies the rectified intelligence to a sufficient power level to drive an electro visual means which is connected at the output thereof The electro visual means used in this form of the invention is a spotlight, which varies visually in amplitude to the amplitude variations of the intelligence passed by the filter The device can be used for pleasure, such as when it is used to observe, in visual form, music, voice, or other sound signals present in electrical form at the output of a radio, a stereo, a public address system, a phonograph, a tape player, etc Or, it can be used as a means of visually identifying the sources of sound contained in the audio range, as well as sources of sound contained in the ranges below and above the audio range The device can contain any number of different channels One of the channels contains a filter, which has a manually adjustable center frequency, which gives the device a search feature, which enables an operator to manually search the sound signal for a particular bit of information contained within the frequency range of the received electrical sound signal The device, also, incorporates automatic gain control to compensate for the changes in the strength of the received electrical sound signal

Mode selection and frequency tuning by injection in pulsed TEA-CO 2 lasers

Abstract: An analytical model is presented which describes certain characteristics of the injection locking of a pulsed TEA-CO 2 laser by means of tunable CW laser radiation. The requirements for SLM generation as the injection frequency is tuned away from line center are discussed. Results indicate the practical importance of the locking time, a parameter which depends on both the injected power and the detuning from the molecular line center frequency.

Multichannel Bragg cells: compensation for acoustic spreading.

Abstract: In some applications, the performance of multichannel Bragg cells is compromised by the spreading of the acoustic waves as they propagate; the spreading causes the signals in the channels to overlap. The overlapping can be significantly reduced by a spatial filter in a Fourier–image plane. The spatial filter is shown to be a cylindrical lens whose power is a function of the distance from the transducer. The effects of changes in the drive frequency as well as those of displacements of the filter are calculated. The reduction in the modulation transfer function as a function of propagation distance is calculated, and some bounds on the time–bandwidth product and the number of channels are dserived. In general, the overall performance can be improved by increasing the center frequency of the Bragg cell while keeping the bandwidth fixed.

Stub type bandpass filter

Abstract: A bandpass filter has a line extending from an input terminal to an output terminal. Three stubs are connected to the line at three different locations on the line at a spacing which is 1/8 of the wavelength, at the center frequency of the passband. Each of the three stubs is short-circuited at a first end and open at a second end and has a total length which is 1/4 the wavelength of said center frequency. The outermost of the three stubs is connected to the transmission line, at a position which is 1/6 the wavelength, from the first end. The intermediate of the three stubs is connected to the line at a position which is either 1/8 or 1/4 the wavelength of the center frequency.

Bandpass filters using electrically-coupled TM010 dielectric rod resonators

Abstract: The authors previously described the design of shielded TM010 dielectric rod resonators (below referred to as “TM010 resonators”), a new configuration of small-size resonators for microwave frequencies. This paper describes the design of bandpass filters using coaxially oriented electrically-coupled TM010 dielectric rod resonators. First, the resonant frequency of electrically-coupled TM010 resonators is analyzed by applying the Ritz-Galerkin method to the integral equations that express the boundary conditions. This method is shown to be effective in numerical calculation of the coupling coefficients and center frequency of the coupled resonators and the resonant frequencies for inserted TM010 resonators which are required for filter design. Next the characteristics of the coupling probe which effectively produces the strong coupling of the axially symmetric TM010 mode of resonators and suppresses the excitation of the higher modes are determined experimentally, making it possible to estimate the center frequency for a filter which takes the variation of the resonant frequency produced by the excitation and coupling hole into consideration. Finally, design of 2- and 3-stage filters of various bandwidths at 2.7 GHz demonstrates the suitability of the approach. Relative bandwidths of 1 to 10%, low losses of. 15 to. 6 db, and absence of spurious responses over bands wider than 1 octave are obtained.

Magnetic recording and reproducing device

Abstract: PURPOSE:To prevent a reproduced signal from deteriorating, by controlling the characteristics of a reproduced signal processing circuit such as a reproductive equalizer according to the tape running speed of reproduction. CONSTITUTION:If the running speed of a tape has deviation from a normal reproduction speed and the frequency axis of the reproduced signal (a) varies, the equalizing characteristics of the equalizer 2, delay characteristics of a filter 3, and discrimination thresh-old of a data discriminator 4 are all optimized by a control signal (f) outputted from a microcomputer 7 according to variation in relative speed. At the same time, the center frequency of a BPF5 and leading-in characteristics and leading-in center frequency of a PLL6 are optimized by the control signal (f) and a switching signal (g) to supply a clock (p) in the best state from the PLL6 to the data discriminator 4.

Synchronizing signal generating apparatus

Abstract: A synchronizing signal generating apparatus comprises a first frequency generator for at least generating a frequency which is 4c times a chrominance subcarrier frequency of B, G, H, and I/PAL systems, where c is a factor of (625×n) and n is an arbitrary positive integer, a second frequency generator for generating a frequency which is (11×n) times a horizontal scanning frequency, a phase control circuit for comparing phases of an output of a first frequency divider which frequency-divides an output signal frequency of the first frequency generator by 1/64489 and an output of a second frequency divider which frequency-divides an output signal frequency of the second frequency generator by 1/(625×n) to supply a phase error signal in accordance with the compared result to the first frequency generator or the second frequency generator to variably control the output signal frequency of the first frequency generator or the second frequency generator, a third frequency divider for frequency-dividing the output signal frequency of the first frequency generator to produce a frequency equal to the chrominance subcarrier frequency, and a fourth frequency divider for frequency-dividing the output signal frequency of the second frequency generator by 1/(11×n).

Probability of Error Measurement for an Interference Resistant Transform Domain Processing Receiver

Abstract: In this paper, the results of implementing a transform domain processing spread spectrum receiver are presented. Measured probability of error results for single tone interference conditions are compared to analytical results, and the improvement in system performance achievable by using a notch filter to attenuate the narrowband interference is demonstrated. The theoretical and experimental results agree very well. Measured probability of error results are also presented for an adaptive system where the notch filter tracks the center frequency of the interferer.

A Monolithic Audio Spectrum Analyzer

Abstract: A monolithic audio spectrum analyzer with 16 channels of bandpass filters, half-wave rectifiers, and postfiltering has been fabricated with double-poly NMOS technology. The chip was designed using switched-capacitor filter techniques. It performs a total of 84 poles of filtering and contains 100 operational amplifiers in an area of 225 X 280 mils. A system dynamic range of better than 43 dB, linearity of better than 1 percent, and center frequency accuracy of better than 1 percent have been achieved.

A monolithic audio spectrum analyzer

Abstract: A monolithic audio spectrum analyzer with 16 channels of bandpass filters, half-wave rectifiers, and postfiltering has been fabricated with double-poly NMOS technology. The chip was designed using switched-capacitor filter techniques. It performs a total of 84 poles of filtering and contains 100 operational amplifiers in an area of 225 × 280 mils. A system dynamic range of better than 43 dB, linearity of better than 1 percent, and center frequency accuracy of better than 1 percent have been achieved.

Frequency modulated railroad track circuit

Abstract: (Case No. 7033) A frequency modulated track circuit arrangement in which a transmitter supplies an FSK signal to the rails, with side frequencies deviating by equal amounts from a central carrier frequency and alternating at a preselected modulation rate. The receiver apparatus includes first and second verification circuit networks coupled to the rails through a band pass filter network which passes only the correct side band frequencies based on the central frequency of the transmitter. The first verification network demodulates only the correct side frequencies and decodes the resulting signal to produce an output only if the modulation rate is correct. The second verification network comprises an amplifier with a predetermined threshold level based on the known attenuation of the transmitted signal by the track circuit and produces an output only if the track signal equals or exceeds this threshold level. The two network outputs, only if both are present, activate an AND gate which supplies an output signal to a delay circuit element which energizes the associated track relay only if the duration of the verification outputs exceeds the preset delay period which eliminates very short noise pulses possibly having true characteristics.

Apparatus for rejecting jamming waves

Abstract: A variable-narrow-band rejection filter is inserted in a reception signal path for rejecting a jamming wave. Signals at input and output terminals of the narrow-band rejection filter are picked up by a pair of first and second bandpass filters each having a center frequency that can be passed thereby which is equal to a rejection frequency of the narrow-band rejection filter. A phase difference between outputs from the bandpass filter is detected by a phase comparator, and the detected signal is supplied through a switch to a hold circuit in which the supplied signal is held. The rejection frequency of the narrow-band rejection filter is adjusted into conformity with the jamming wave frequency by an output from the hold circuit. The levels of the output signals from the first and second bandpass filters are detected respectively by a pair of first and second level detectors, and the detected outputs are compared by a comparator. The foregoing switch is kept off as long as the level of the signal at the input terminal of the narrow-band rejection filter is smaller than the level of the signal at the output terminal thereof.