Showing papers on "Fundamental frequency published in 1979"

High-Accuracy Analog Measurements via Interpolated FFT

Abstract: By use of an interpolated fast-Fourier-transform (FFT) algorithms are developed for multiparameter measurements upon periodic signals. Eight pertinent measurements, such as fundamental frequency, phase, and amplitude, are made with enhanced accuracy compared to existing algorithms, including tapered-window-FFT algorithms. For the more general case of nonharmonic multitone signals also the method is shown to yield exact amplitudes and phases if the tone frequencies are known beforehand. These measurements are useful in a variety of applications ranging from analog testing of printed-circuit boards to measurement of Doppler signals in radar detection.

The perception of fundamental frequency declination

Abstract: A series of experiments was carried out to investigate how fundamental frequency declination is perceived by speakers of English. Using linear predictor coded speech, nonsense sentences were constructed in which fundamental frequency on the last stressed syllable had been systematically varied. Listeners were asked to judge which stressed syllable was higher in pitch. Their judgments were found to reflect normalization for expected declination; in general, when two stressed syllables sounded equal in pitch, the second was actually lower. The pattern of normalization reflected certain major features of production patterns: A greater correction for declination was made for wide pitch range stimuli than for narrow pitch range stimuli. The slope of expected declination was less for longer stimuli than for shorter ones. Lastly, amplitude was found to have a significant effect on judgments, suggesting that the amplitude downdrift which normally accompanies fundamental frequency declination may have an important role in the perception of phrasing.

The air gun impulsive underwater transducer

Abstract: We are reporting our experience with the use of high‐pressure guns at many depths to generate impulsive underwater sound in the fundamental frequency range from 10 to 200 Hz. Air guns are not often used outside of seismic exploration, but they have potential as cheap, energetic, impulsive sources of low‐frequency sound. A simple analysis shows that the fundamental frequency of waveforms increases faster with increasing depth than predicted by the Rayleigh–Willis equation. In addition, the acoustical efficiency of air gun sources is found to decrease with increasing depth, falling sharply as the ambient pressure becomes a significant fraction of the initial gun pressure. Experimental waveform and energy source level data verify these analytical results. Finally, data obtained from arrays of air guns are presented. These data demonstrate that air guns may be successfully arrayed and that the internal impedance of the air gun source is high enough that each air gun resembles a constant source strength (volume velocity) source, resulting in more radiated energy than expected from constant energy sources for some spacings.

Double-Drift Beam Bunching Systems

Abstract: The double-drift beam bunching system consists of two bunchers that are separated in space, independently driven but phase-locked together. The second buncher to be encountered by the beam is driven at twice the frequency of the first. This system offers an attractive alternative to conventional one- and two-frequency systems since it's bunching efficiency is about twice that for a single frequency system and about 25% larger than that for a two-frequency system in which both harmonics are imposed on the same electrode. The independence of the two bunchers provides for greater ease in the adjustment and stabilization of the rf amplitudes and phase to the accuracy of ±1% and ±0.5° that is required. A double-drift system, designed to operate at 4.5 to 14 MHz, has been installed on the ORNL EN-tandem and evaluated using 16O, 32S, 58Ni, and 63Cu ion beams. Performance was in close agreement with predictions; about 60% of the dc beam was bunched into a phase angle of 6° of the fundamental frequency. A brief discussion of the principles of operation, predicted performance and practical design considerations are given. Results of a theoretical study of the dynamic focussing effects and energy-modulation imperfections of ungridded klystron bunchers are presented as approximate formulas.

Flexural vibrations of certain full and annular composite orthotropic plates

Abstract: The uncoupled equation of motion for the flexural displacement of an orthotropic composite circular plate having symmetric lamination is presented. A numerical method is employed to calculate the symmetric and nonsymmetric vibrational frequencies of full and annular composite plates subjected to a variety of boundary conditions. Effects produced by lamination interchange and fiber reversal are discussed; in particular, certain laminations are capable of producing a higher fundamental frequency than either of the constituent materials alone can attain. For annular plates it is found that for certain lay‐ups the fundamental frequency derives from a nonsymmetric mode. Finally, pinhole‐center annuli are examined and, for a free inner edge, a comparison is made with corresponding full‐plate frequencies.

Pitch extraction from corrupted harmonics of the power spectrum

Abstract: Unlike most frequency domain methods for pitch extraction, here the pitch is computed from a few selected high quality peaks in the spectrum, achieving greater reliability. A new approximate greatest common devisor (AGCD) algorithm is proposed to compute the fundamental frequency of a given set of corrupted harmonics. Authentic harmonic peaks ar4e obtained by logical filtering of the spectrum and the computed fundamental frequency is subjected to an error test using the best of the harmonic peaks. Thus the algorithm provides a voiced–unvoiced decision, as well as the pitch for voiced regions. The results are uniformly good for male and female voices, and error rates are comparable to those for the best algorithms reported in the literature.

Digital memory system

Abstract: A digital memory system adapted to store samples of a received radio frequency signal and enable retransmission of a radio frequency signal from such stored samples, such retransmitted radio frequency signal having a frequency related to the frequency of the received radio frequency signal. The received signal is heterodyned to a periodic sinusoid video frequency signal having a predetermined average level. A sequence of one-bit logical signals representative of the amplitude of the video signal relative to a predetermined level other than the predetermined average level is stored. The stored samples are returned and converted to a radio frequency signal having a frequency of the received signal. By using a non-average level as the threshold voltage, the spectrum of the signal retrieved from the memory will have reduced harmonic components relative to the fundamental frequency component.

Surface acoustic wave resonators utilizing harmonic frequencies

Abstract: A surface acoustic resonator including an interdigital transducer configured to generate acoustic waves at at least one harmonic frequency, and a pair of reflection gratings capable of essentially total reflection of the acoustic waves in both fundamental and harmonic modes of operation. One-port and two-port resonators are disclosed, capable of operation at fundamental and harmonic frequencies, to provide a higher frequency of operation without correspondingly higher resolution requirements for manufacturing processes. For single-mode operation at higher frequencies, the interdigital transducer and reflection gratings have different fundamental frequencies, and utilize harmonics of different order but the same actual frequency, such that the resonator functions at a single frequency, which may be, for example, the third harmonic with respect to the transducer fundamental frequency, and the second harmonic with respect to the reflection grating-fundamental frequency.

Apparatus and method for audiometric assessment

Abstract: An apparatus for producing sounds of selectable pitch, quality and sound pressure level and a method for using the apparatus in assessing a person's hearing are disclosed. The apparatus includes a function generator for generating the fundamental frequency of the sound to be produced, a formant filter circuit for passing only one or more resonant frequencies of the fundamental frequency so as to vary the quality of the sound to be produced, and a level control for varying the loudness of the sound to be produced. The method of the invention includes adjusting the apparatus of the invention so as to produce sounds similar to those a patient produces in his own speech and using such sounds to assess the patient's hearing skills.

Transducer positioning system

Abstract: A servo system for centering a transducer over boundaries between adjacent servo tracks on a magnetic disk in which the servo tracks are each formed by alternate long and short magnetic segments, with the short segments in one track being centered with the long segments of adjacent tracks. The servo system includes a frequency doubler circuit for producing a uniform frequency square wave signal of double the fundamental frequency of the analog signal picked up by the transducer from the servo encoding, a filter connected with the transducer for producing an analog double frequency signal based on the analog signal from the transducer, a synchronous detector functioning as a multiplier for multiplying the double frequency square wave signal with the analog double frequency signal from the transducer, and a filter for averaging the resultant pulsating position error signal to provide a steady state position error signal for any particular position of the transducer over a pair of adjacent servo tracks. The steady state position error signal is applied to a servo control and servo actuator for moving the transducer until the steady state position error signal reaches zero which corresponds with the desired centered position of the transducer over the boundary between a pair of adjacent servo tracks.

Frequency following circuit

Abstract: A plurality of a signal peak detection circuits connected in cascade for operation on a complex waveform input signal, for generating a reference signal having peaks occurring in time with the peaks of the fundamental frequency component of the input signal. The reference signal is processed for producing a voltage proportional to the period between successive signal peaks, which voltage is successively stored and monitored at select times for comparison of the relative magnitude changes in the voltage, for updating an output control voltage.

Frequency synthesizing system for AM·SSB transceiver

Abstract: A frequency synthesizing system for use in an AM·SSB transceiver of double conversion type comprising a single crystal oscillator in its PLL synthesizer. The fundamental frequency of the PLL synthesizer provided by the oscillation of the crystal oscillator is selected to be n times (where n is an even number) the second intermediate frequency of the transceiver so that all the frequencies required for the operation of the AM·SSB transceiver can be derived from the oscillation frequency of the single crystal oscillator, whereby to simplify the structure of the AM·SSB transceiver and to facilitate the adjustment of the transceiver.

Apparatus and method for generating waveforms which are particularly suitable for a PWM-driven motor

Abstract: A triangle waveform having substantially linearly sloped, gradually increasing and decreasing edges and having a frequency nf is generated from an n-phase sine wave signal, each phase having a fundamental frequency f. A segment of any of the n-phases of the sine wave is detected when that segment is within a predetermined angular amount from a reference crossing level, such as the zero crossing of the sine wave signal. Successive ones of the detected segments are selected to synthesize the triangle waveform. In the preferred use of this invention, the triangle waveform is compared to a reference signal, such as the sine wave signal from which the triangle waveform is generated, this reference signal having a controllable frequency and amplitude. Pulse transitions are generated at the intersection of the triangle waveform and each of the respective phases of the reference signal. In one embodiment of this invention, the frequency of the triangle waveform is increased by an amplitude-folding technique wherein the triangle waveform (of frequency nf) is folded about a pair of equal but opposite folding levels whenever the triangle waveform reaches either of these levels, so as to produce an amplitude-folded triangle waveform of frequency mf and of peak levels determined by the folding levels.

Method of and system for determining the pitch in human speech

Abstract: Method of and arrangement for the determination of the pitch of speech signals in a system of speech analysis, wherein sequences of significant peak positions of the amplitude spectrum of a speech signal are derived (13) from time segments of the speech signal by means of a discrete Fourier transform (12). In order to reduce the influence of noise signals and noise components, respectively, in the amplitude spectrum the significant peak positions are compared with different masks (15), which have apertures at harmonic distances of the associated fundamental tone. The mask which matches the sequence of significant peak positions best is selected (20). A probable value for the pitch is now computed with the harmonic numbers now known of the significant peak positions which are located in apertures of the selected mask. The mean square error between these significant peak positions and the corresponding harmonics of the finished tone can be used as a criterion (21).

A Single-Cavity Double-Frequency Buncher

Abstract: A single-cavity buncher has been developed that resonates at both the fundamental and twice the fundamental frequency to form a more nearly ideal bunching voltage waveform in the gap. The cavity utilizes the TM020-like mode as the first harmonic of the fundamental TM010-like mode. Field distributions on or near the axis, which are seen by the beam, are essentially identical for the two modes. Many beam bunching applications require two bunchers with the harmonic buncher being physically as close as possible to the fundamental frequency buncher - the buncher described here accomplishes this property with a single cavity and excitation of two modes. Calculated parameters for cavity designs with a fundamental frequency of 0.45 GHz are presented for different cavity lengths which represent a range of interest for accelerators and rf tubes. Means of tuning and fabrication are described. A geometry chosen for PIGMI is described in more detail.

Optimal control of the natural frequency of a plate of variable thickness

Abstract: PLATE SHAPE optimization is considered, such that the fundamental frequency of the plate is a maximum for given lower and upper bounds on the weight and thickness of the plate. The existence of an optimal control is proved, and the solutions of the appropriate finite-dimensional problems are shown to be convergent to the solution of the initial infinite-dimensional optimal control problem.

Method for magneto-optical current measuring.

Abstract: of EP00043211. A method of magneto-optical current measurement utilising that rotation of the polarisation plane of a linearly polarised light beam which is dependent upon the current and on which is superimposed a high-frequency modulating rotation, the total rotation being converted into a change in intensity of the light beam, and this change being converted into an electric measuring signal, characterised in that separate frequency bands having the fundamental frequency and the first harmonic of the modulation signal as respective centre frequencies are filtered from the measuring signal, the frequency band of the harmonic and that of the fundamental frequency being subsequently demodulated, and the quotient of the two demodulation signals then being formed.

Vowel perception: The relative perceptual salience of selected spectral and waveform manipulations

Abstract: The objective of the preliminary research to be described is to quantify the psychophysical similarity of vowel‐like stimuli that differ in certain spectral and waveform characteristics. To that end, the vowel /ae/has been synthesized by adding together sinusoidal harmonics of the appropriate frequencies, amplitudes, and phases. Changes to these parameters and to fundamental frequency are made on a period‐by‐period basis. The resulting synthetic waveform is essentially indistinguishable from that produced by a conventional cascade formant synthesizer, but the present synthesis technique permits the experimenter to manipulate certain spectral and temporal details more easily. A set of 65 different vowels acoustically similar to /ae/have been synthesized by manipulating formant frequencies, formant bandwidths, spectral tilt, phase relations among harmonics, and filtering passband/stopband. Subjects are asked to estimate the psychophysical distance between each stimulus and a reference vowel in a 380‐trial ran...

Harmonic properties of the annular membrane

Abstract: Properties of a vibrating annular membrane are analyzed mathematically and numerically to investigate the relative harmonicity of the higher‐order modes compared with the fundamental mode. The harmonicity depends on the zeros of a cross‐product of Bessel functions. For a ratio of external‐to‐internal diameter up to about 1.2, the higher modes have frequencies which are very nearly exact integer multiples of the fundamental frequency. For circularly symmetric modes, the ratio of all higher radial mode frequencies to exact harmonic values is less than 1.0006 (a logarithmic cent), a ratio imperceptible to a listener. Angle‐dependent modes also give good harmonicity, especially if some lower radial modes are suppressed. Thus the modes of an annular membrane whose external‐to‐internal diameter ratio is less than 1.2 are much more harmonic than those of the full circular membrane of a conventional drum. The theoretical harmonicity is at least as good as reported for stringed melodic instruments (piano, violin). The analysis suggests characteristics for construction of an annular drum‐head which is supported on concentric rims of two cylinders; to sound the drum, a braced hoop might be used to excite radial modes, or strikers with grooved faces might be used to excite angular modes without exciting lower radial modes.

Fundamental frequency switching control system in frequency synthesizing unit

Abstract: PURPOSE:To shorten the time required for anomaly detection, by switching current and auxiliary units when the time change rate of the output level of the LPF exceeds a fixed value in respect to current and auxiliary units for fundamental frequency generation dependent upon a PLL circuit CONSTITUTION:In current and auxiliary fundamental frequency generating units consisting of main oscillators 1 and 1' and PLL circuits 2 and 2', outputs of LPFs 22 and 22' are subjected to A/D conversion by converters 6 and 6' and are stored in memories 7 and 7' Digital values stored in memories and digital values of A/D converters are compared with each other by comparators 8 and 8' If memories and comparators use fundamental frequencies fi and fi' of main oscillators as sampling pulses, comparators detect equivalently the difference between two digital values different in period, namely, the time change rate of the LPF output signal level In case that this difference exceeds a fixed value, change-over switches 3 and 3' are switched through control circuit 5 to perform switching from the current unit to the auxiliary unit or from the auxiliary unit to the current unit

Extraction unit for fundamental wave signal

Abstract: PURPOSE:To extract effectively and definitely only fundamental components from an input signal by proviing a variable characteristic filter which allows fundamental frequency components of the input signal including higher harmonics to pass through and by controlling this filter with the output of a fundamental wave detection circuit CONSTITUTION:An input signal including a higher harmonic of a sound of a musical instrument performance is supplied to voltage control type variable characteristic filter 20 and fundamental wave detection circuit 22 via buffer 12 Circuit 22 is equipped with LPFs 23a, 23b with their frequencies set higher in sequence, whose output signals are detected by signal detection circuits 24a, 24b The sequence of the lowest-pass LPF 23a is supplied from circuit 24a to gate element 26a directly, but sequences of other LPFs 23b, 23c are inputted to gates 26b, 26c through AND circuits 25b, 25c , and 27, and inverters 28b, 28c and filter 20 is controlled by gate outputs Consequently, the output signal of the lowest-pass filter LPF allowing the input signal to pass through is generated and signals of other filter sequences are inhibited, so that only fundamental wave components will be extracted

Third harmonic generation in two-photon interaction between high-power coherent optical pulses and resonant media

Abstract: A numerical investigation is made of third harmonic generation (THG) under conditions of two-photon resonance between the fundamental frequency and a selected transition in the atoms of a medium. It is shown that under conditions of coherent interaction between the pump pulse and the medium, a THG efficiency of ~20% or higher may be achieved. In this case, THG in the form of high-power ultrashort pulses may be obtained. It is shown that experimental observation of similar effects in specific media should not present particular difficulties.