Showing papers on "Bandwidth (signal processing) published in 1976"

Auditory filter shapes derived with noise stimuli

Abstract: A wide‐band noise having a deep notch with sharp edges was used to mask a tone. The notch was centered on the tone, and threshold was measured as the width of the notch was increased from 0.0 to 0.8 times the tone frequency (0.5, 1.0, or 2.0 kHz). The spectrum level of the noise was 40 dB SPL. If it is assumed that the auditory filter is reasonably symmetric at these intensities, then the shape of the filter centered on the tone can be estimated from the first derivative of the curve relating tone threshold to the width of the notch in the noise. The 3‐dB bandwidths of the filters obtained were about 0.13 of their center frequency. In the region of the passband, the Gaussian curve provides a good approximation to the shape of the derived filters. The equivalent rectangular bandwidths of the Gaussian approximations are about 0.20 of their center frequency, which is comparable to the critical‐band estimates of R. Zwicker, G. Flottorp, and S. S. Stevens [’’Critical bandwidth in loudness summation,’’ J. Acoust. Soc. Am. 29, 548–557 (1957)]. The Gaussian approximation cannot be used outside the passband, because the tails of the derived filters do not fall as fast as the Gaussian curve. Subject Classification: [43]65.58, [43]65.35; [43]80.50.

An algorithm for reducing the bandwidth and profile of a sparse matrix

Abstract: A new algorithm for reducing the bandwidth and profile of a sparse matrix is described. Extensive testing on finite element matrices indicates that the algorithm typically produces bandwidth and profile which are comparable to those of the commonly-used reverse Cuthill–McKee algorithm, yet requires significantly less computation time.

The waveguide laser - A review

Abstract: The present article reviews the fundamental physical principles essential to an understanding of waveguide gas and liquid lasers, and the current technological state of these devices. At the present time, waveguide laser transitions span the visible through submillimeter regions of the wavelength spectrum. The introduction discusses the many applications of waveguide lasers and the wide variety of laser configurations that are possible. Section 1 summarizes the properties of modes in hollow dielectric waveguides of circular, rectangular, and planar cross section. Section 2 considers various approaches to optical feedback including internal and external mirror Fabry-Perot type resonators, hollow waveguide distributed feedback structures, and ring-resonant configurations. Section 3 discusses those aspects of molecular kinetic and laser theory pertinent to the design and optimization of waveguide gas lasers such as the scaling laws for discharge-excited gas lasers, molecular models useful in maximizing the oscillation bandwidth, the effects of gas flow rate, and the physics of optically-pumped far-infrared lasers. Finally, a review of the waveguide gas and liquid lasers reported to date is given in Section 4.

The Capture Effect in FM Receivers

Abstract: In this paper a theoretical explanation of the capture effect is given by calculating the instantaneous frequency of the output signal of a limiter when two frequency modulated (FM) signals are present at the limiter input. When this signal is applied to a demodulator with unlimited bandwidth, the output signal of the demodulator proves to have an extreme capture effect. When however the demodulator bandwidth is limited, the capture effect is shown not be be extreme. This phenomenon is explained and possibilities are given to minimize the capture effect. Some of the results of measurements on limiters and demodulators are given in this paper; they prove that a weak capture effect can be obtained. A method of calculating the degree of capturing is included.

A digital filter bank for spectral matching

Abstract: A new digital filter bank design is proposed for the processing of speech waveforms where spectral pattern matching techniques are applicable. Outputs in decibels from the 30 channels of the filter bank are computed every 12 ms. Care has been taken to select a time window and filter center frequency and bandwidth values that take into account the acoustic characteristics of speech. A distance metric is proposed for comparing a spectral frame with previously derived reference patterns. The metric incorporates procedures for crude speaker/microphone normalization, signal level normalization, background noise normalization, and procedures for emphasizing differences in the region of spectral peaks.

Analysis of Transit Time Effects on Doppler Flow Measurement

Abstract: A relation is derived between the transmitted spectral density and the output spectral density of broad bandwidth, random signal, Doppler flow measurement systems operating under conditions where the fluid transit time is limited by the transmitted signal bandwidth and not by beam geometry. The fact that this result is already known to hold for pulsed radio frequency (RF) Doppler proves that random or pseudorandom Dopplers will give the same output spectrum as pulsed RF Dopplers, provided that the transmitted spectral density of the RF system has the same envelope as that of the noise system.

The input admittance of the rectangular cavity-backed slot antenna

Abstract: The input admittance of the rectangular cavity-backed slot antenna is investigated. The slot is assumed narrow so that the voltage distribution in its aperture is sinusoidal. Equations which represent the input admittance of this slot, backed by a rectangular cavity in which a single propagating wave is assumed to exist, are given. Calculations based on these representations are compared to available measured data. As the depth of the cavity increased the resonant frequency decreased and the bandwidth became narrower. Input admittance curves as a function of electrical slot length are also presented for several size cavities.

A Feedback Receive Amplifier for Optical Transmission Systems

Abstract: We consider the design and implementation of a lownoise feedback receive amplifier for use in optical communication systems. The feedback amplifier configuration is advantageous in that it offers a wide bandwidth with good signal to noise ratio.

Performance of Phase-Locked Loops in the Presence of Fading Communication Channels

Abstract: An approach is presented for the analysis of phase-locked loops whose input signal has passed through time-varying channels. The specific channels considered in detail are the Rice-Nakagami, Rayleigh, and lognormal fading channels. Loop performance is characterized in terms of the steady-state probability density function of the reduced phase error process. The basic parameters which characterize performance include the loop signal-to-noise ratio (SNR) and the variance and bandwidth of the fading components introduced by the channel. Particular channel models are used to illustrate the theory for the firstorder loop. The results are also applied to the analysis of the PSK noisy reference problem in the presence of these time-varying channels.

Interference canceling method and apparatus

Abstract: Apparatus for canceling interference suitable for use in conjunction with stationary phased array antennas or transducer arrays designed for satellite or other communication systems employing N-phase PSK (Phase Shift Keying) modulation is disclosed. The techniques used in the apparatus involves processing of signals received by a main array and an auxiliary array of a phased array antenna so that an error signal is derived which is fed back to circuitry which modifies at least one signal received by the auxiliary array. The modified signal or signals are summed with the signal received by the main array so that a sum wave is generated whose interference component is minimal. The feedback circuitry exponentiates or raises the sum wave to the N th power to eliminate modulation, since the N th power of an N-phase PSK signal is a narrowband carrier. Then a term proportional to the desired signal raised to the N th power is filtered from the exponentiated sum wave and the remainder is utilized for error signal purposes. This technique operates without sacrificing bandwidth or degrading the desired signal and permits reception of signals with frequency spectra substantially overlapping one another.

A 500-stage CCD transversal filter for spectral analysis

Abstract: The operation and design of 500-stage charge-coupled device (CCD) transversal filters are described. The filters have been mask programmed for implementing two spectral analysis techniques: 1) bandpass filtering and 2) Fourier analysis using the chirp z transform (CZT) algorithm. The bandpass filter has a measured fractional 3 dB bandwidth of 0.0108 and 38 dB sidelobe rejection. The dynamic range is 75 dB with less than 45 dB total harmonic distortion. A sliding transform is defined which is useful for calculations of the power spectral density and is shown to be particularly advantageous in a CCD-CZT implementation. Using the sliding transform, a 500-point spectrum is calculated using CCD's with resolutions which can be varied from 1-200 Hz. The dynamic range of the power spectral output was measured to be 80 dB. A discussion is given of the performance limitation of a general CCD filter due to the inherent characteristics of the device. The results are evaluated for the 500-stage devices described above and indicate that sample rates from 25 Hz to 10 MHz are possible with a dynamic range approaching 100 dB while retaining high linearity.

Acoustoelectric convolvers for programmable matched filtering in spread-spectrum systems

Abstract: Acoustoelectric convolvers for a spread-spectrum communication application age described with a 100-MHz bandwidth. The use of convolvers as programmable matched filters provides the ability to change the coding waveform from bit-to-bit, thus offering improved multipath performance, security against decoding, and protection against repeat jamming. In this paper, we describe design and performance details of a prototype convolver which processes signals of 10-µs duration with a 100-MHz bandwidth. A dynamic range of 50 dB is obtained, and error signals are 30 dB below the output signal with input signal levels of +14 dBm. A test circuit is described which creates typical spread-spectrum signals in which each bit is encoded into 512 chips and data is encoded by inverting the phase of an entire bit at a data rate of 100 kbits/s.

Noise‐intensity discrimination: Effects of bandwidth conditions and mode of masker presentation

Abstract: Noise‐intensity discrimination was studied as a function of both signal and masker bandwidth. Five bandwidths of noise—ranging from 100 to 10 000 Hz—were employed. Maskers were presented at each of three spectrum levels (5, 25, and 45 dB re 0.0002 μbar). Discrimination thresholds were relatively unaffected by changing bandwidth over a two‐decade range when the signal and masker were filtered together, with either continuous or gated presentation of the masker. When the masker bandwidth was greater than that of the signal, the reciprocity between signal power density and signal bandwidth was found to be 5 dB per log unit of bandwidth with continuous maskers and 5–10 dB (depending upon level) with gated maskers. The results were compared with predictions of energy‐detector models of noise‐intensity discrimination. Modifications of simple energy‐detection schemes were discussed.Subject Classification: [43]65.58, [43]65.75, [43]65.50; [43]50.70.

Surface Acoustic Wave Ring Filter

Abstract: A surface acoustic wave low loss filter device having input and output transducers located along opposed sides of a rectangular propagation path with frequency selective reflective gratings at each of the four corners of the rectangle. Two traveling surface waves traverse the device along opposed paths encountering frequency filtering at the gratings. The two waves arrive at the output transducer additively in phase eliminating the bidirectionality loss normally associated with surface acoustic wave devices. At frequencies for which the gratings are reflective there can be nearly lossless transmission from input to output. At all other frequencies, transmission between input and output transducers is negligible. The device has high sidelobe rejection, adjustable passband skirt slopes, and an adjustable bandwidth.

Algorithm 508: Matrix Bandwidth and Profile Reduction [F1]

Abstract: This program, REDUCE, reduces the bandwidth and profile of sparse symmetric matrices, using row and corresponding column permutations. I t is a realization of the algorithm described by the authors in [4]. I t was extensively tested and compared with several other programs [5] and was found to be considerably faster than the others, generally superior for bandwidth reduction and as satisfactory as any other for profile reduction.

Adaptive Haar Transform Video Bandwidth Reduction System For RPV' s

Abstract: A practical video bandwidth compression system is described in detail. Video signals are Haar transformed in 2 dimensions and the resulting transform coefficients are adaptively filtered to achieve reduced transmission data rates to less than 1 bit/pel, while maintaining good picture quality. Error detection and compensation is included into the transmission bit structure.© (1976) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The influence of stimulus bandwidth on localization of sound in space

Abstract: The ability of listeners, deprived of prominent interaural time and intensity cues, to locate noise bands differing in width was investigated. To minimize binaural cues, we placed the sound source at various positions in the median sagittal plane. To eliminate binaural cues, we occluded one ear. The stimuli consisted of broadband noise and bands of noise centered at 8.0 kHz. The width of the latter ranged from 1.0 to 6.0 kHz. The results from seven listeners showed that localization proficiency for sounds in the median sagittal plane decreased with decreases in bandwidth for both binaural and monaural listening conditions. This function was less orderly for monaural localization of horizontally positioned sounds. Another consequence of a reduction in bandwidth was an increasing tendency of listeners to select certain loudspeakers over others as the source of the sound. A previous finding showing that localization of sound in the median sagittal plane is more accurate when listening binaurally rather than monaurally was confirmed.

Wideband, Noncoherent, Frequency-Hopped Waveforms and Their Hybrids in Low-Probability-of-Intercept Communications

Abstract: : Frequency hopping is a commonly used technique for achieving wide spread spectrum bandwidths in intercept-resistant and interference-resistant communications. This report develops the techniques necessary to determine the contribution of a frequency-hopped modulation to communication system detectability, independent of such scenario-related parameters as relative geometry, antenna gains, and link margins. A variety of frequency-hopped modulation schemes, associated processing techniques, and losses are discussed. Optimum intercept receivers are considered in order to place a theoretical bound on a signal detectability. This, in turn, leads to the development of quality factors which permit any analysis of the impact of waveform parameters alone on convertness. A parametric analysis is performed in terms of these quality factors for a large family of modulations. The result is a small subset of signals optimized for convertness, consisting of fast hop pulsed waveforms and slow hop continuous waveforms, both with pseudonoise hop bandwidth spreading. Selection of the final modulation must ultimately depeend on such additional system synchronization time, implementation complexity, and jam resistance. The impact of these factors is discussed qualitatively.

Microwave level gaging system

Abstract: A method and apparatus for measuring liquid level. A generated broad-band swept-frequency C.W. microwave signal (2-4 GHz) is upverted to a high frequency band signal (34-36 GHz), which is transmitted towards, and reflected from, a liquid surface. The reflected signal is downverted to the frequency band of the original generated signal, and then the phase difference between the original and downverted signals is measured by a microwave phase discriminator and a quantizer, which generates video pulses proportional to the total phase shift across the swept C.W. band. During an adjacent sweep in the same direction, the original signal is compared with a signal transmitted through a calibration cable equivalent to a known free-space path length. The unknown signal path to and from the liquid surface, can then be calculated by comparison of the video pulse train outputs during the CALIBRATE and OPERATE modes of operation, either by the ratio of the number of pulses, or the average time between pulses during each sweep. Alternately, the mode of operation can be switched several hundred times during a single sweep across the bandwidth, and the unknown signal path corresponding to a particular liquid level can be calculated by comparison of the spacing during adjacent CALIBRATE and OPERATE modes to give several hundred measurements at different frequencies. Deviate measurements can then be eliminated, and the remaining measurements can be averaged to give a highly accurate true average measurement by known methods.

Effects of Finite-Bandwidth Driver Pumps on the Parametric-Decay Instability

Abstract: The effects of a finite-bandwidth driver pump on the parametric-decay instability are investigated experimentally. The results include the dependence of threshold power, growth rate, and saturation level on the bandwidth of several coherently and randomly modulated pumps.

Light-emitting diodes with a modulation bandwidth of more than 1 GHz

Abstract: The design principle and the fabrication of high-speed l.e.d.s with a 3dB modulation bandwidth in the gigahertz range is described. The modulation characteristic, radiance and spectrum have been measured. The results demonstrate that these l.e.d.s are suited as light generators in optical transmission systems with a bandwidth in excess of 1 GHz.

Auditorium simulator economizes on delay line bandwidth

Abstract: A filter network for use with an acoustic signal reproduction system having at least two, spatially separable, speaker means each capable of reproducing acoustic waves from corresponding electrical signal. The network includes a frequency divider for separating an electrical signal representative of acoustic waves into first and second components, the first component including primarily those audio frequencies, which when acoustically reproduced tend to provide unambiguous binaural phase localization. The second component includes primarily those audio frequencies which when acoustically reproduced tend not to provide unambiguous binaural phase localization. The network also includes structure for delaying the first component for a predetermined period of time to produce a delayed signal so that when the combined first and second components are applied to one of the speaker means and the combined second component and the delayed signal are applied to the other of the speaker means the acoustic field produced tends to simulate spaciousness or ambience of a larger room than the actual listening area.

Bandwidth switching circuit for intermediate frequency amplifier stage in FM receiver

Abstract: This invention provides a bandwidth switching circuit for an intermediate frequency amplifier stage in an FM receiver that insures clear reception of desired signals by automatically switching the intermediate frequency amplifier stage between the wide and narrow bandwidths according to the radio field conditions. The bandwidth switching circuit includes a detector for detecting beat components due to interference contained in received signals and a change-over switch for switching the bandwidth switching circuit according to signals detected by the detector, whereby the bandwidth of the intermediate frequency amplifier stage is automatically switched depending on whether the beat components are present or not.

Spectral occupancy of digital angle-modulation signals

Abstract: The spectral or band occupancy of an RF signal is often defined as the bandwidth that contains a specified fraction (usually 99 percent) of the modulated RF power. The band occupancy of binary and quaternary PSK signals with and without RF filtering and with modulation pulses of several shapes has been evaluated and the results presented in graphical and tabular form. For a binary FSK signal with phase deviation of ± π/2, sometimes called an FM-PSK signal, numerical values of the spectral occupancy with rectangular and raised-cosine signaling have been obtained and the results given in graphical form. For a binary PSK signal with signaling rate 1/T and with arbitrary baseband pulse shaping, we have derived a lower bound on the fraction of the continuous power contained outside any given band, but have not been able to get a bound on the total band occupancy. However, for an FM-PSK signal, a lower bound on the total band occupancy has been derived, and it is shown that the value of this lower bound for 99-percent power occupancy is 1.117/T. The 99-percent power occupancy bandwidth of an FM-PSK signal is 1.170/T with rectangular signaling and 2.20/T with raised-cosine signaling.

Amplitude selectivity versus constant delay in minimum-phase lossless filters

Abstract: A classic filter problem is the construction of minimumphase transfer functions which simultaneously possess linear phase in the passband and steep amplitude selectivity. This paper presents a detailed quantitative treatment of this problem for lossless transducers, and it is shown that the bandwidth for linear phase is strictly constrained independent of the complexity of the transducer once the amplitude selectivity is prescribed. Prototype, but nonrational, physically realizable transfer functions are constructed which satisfy the bandwidth constraints, and polynomials which approximate the prototypes are then calculated to yield physical LC linear phase ladder networks. The resultant structures, though minimum phase, can have respectable selectivity and phase properties. For example, an 8-element ladder is synthesized which realizes flat delay to ± 2.5 percent over 80 percent of the passband, with 60 dB of loss at twice cutoff, and 3-dB passband tolerance. Finally, the paper shows how to further improve amplitude selectivity at the price of small amounts of nonlinear phase distortion, and quantitative measures of this improvement are presented.

Input filtering apparatus for loudspeakers

Abstract: Improved input filtering apparatus for loudspeaker systems, and loudspeaker systems including such apparatus. The bass roll-off point of input filtering apparatus for loudspeakers is automatically adjusted to an optimum in accordance with the amplitude and spectral content of the audio signal being received at the time, thereby attenuating components in the signal liable to cause "bottoming" of the loudspeaker. The input filter apparatus comprises a first high-pass filter having a breakpoint frequency at or near the lower threshold of the audio frequency range, a second variable bandwidth, high-pass filter connected to receive the first high-pass filter output, a feedback circuit responsive to the second filter output to provide a feedback signal as a linear function thereof with a gain which is substantially inversely proportional to the square of the frequency, and circuit means including threshold means connected with the second filter and responsive to the said feedback signal to relatively rapidly increase the breakpoint frequency of the second filter in response to values of the feedback signal which exceed a threshold and to relatively showly reduce that breakpoint frequency in response to values of the feedback signal which do not exceed the said threshold. Bass equalization circuit means having a frequency response at the low end of the audio spectrum which is substantiallythe inverse of the frequency response of said loudspeaker means are provided between the output of the second filter and the loudspeaker drive circuit.