Showing papers on "Fundamental frequency published in 1973"

A study of locking phenomena in oscillators

Abstract: Impression of an external signal upon an oscillator of similar fundamental frequency affects both the instantaneous amplitude and instantaneous frequency. Using the assumption that time constants in the oscillator circuit are small compared to the length of one beat cycle, a differential equation is derived which gives the oscillator phase as a function of time. With the aid of this equation, the transient process of "pull-in" as well as the production of a distorted beat note are described in detail. It is shown that the same equation serves to describe the motion of a pendulum suspended in a viscous fluid inside a rotating container. The whole range of locking phenomena is illustrated with the aid of this simple mechanical model.

An optimum processor theory for the central formation of the pitch of complex tones

Abstract: A comprehensive theory is formulated for the central formation of the pitch of complex tones, i.e., periodicity pitch [Schouten, Ritsma, and Cardozo, J. Acoust. Soc. Amer. 34, 1418–1424 (1962)]. This theory is a logical deduction from statistical estimation theory of the optimal estimate for fundamental frequency, when this estimate is constrained in ways inferred from empirical phenomena. The basic constraints are (i) the estimator receives noisy information on the frequencies, but not amplitudes and phases, of aurally resolvable simple tones from the stimulus and its aural combination tones, and (ii) the estimator presumes all stimuli are periodic with spectra comprising successive harmonics. The stochastic signals representing the frequencies of resolved tones are characterized by independent Gaussian distributions with mean equal to the frequency represented and a variance that serves as free parameter. The theory is applicable whether frequency is coded by place or time. Optimum estimates of fundamental frequency and harmonic numbers are calculated upon each stimulus presentation. Multimodal probability distributions for the estimated fundamental are predicted in consequence of variability in the estimated harmonic numbers. Quantification of the variance parameter from musical intelligibility data in Houtsma and Goldstein [J. Acoust. Soc. Amer. 51, 520–529 (1972)] shows it to be dependent upon the frequency represented and not upon other stimulus frequencies. The quantified optimum processor theory consolidates known data on pitch of complex tones.

Discrimination of fundamental frequency contours in synthetic speech: implications for models of pitch perception

Abstract: The just‐noticeable difference (JND) for selected aspects of voice fundamental frequency (F0) contours was determined by varying the F0 control parameter of a digitally simulated terminal analog speech synthesizer. Data were obtained from three subjects for a number of 250‐msec segments of the synthetic vowel /ɛ/ differing only in fundamental frequency. Results indicate that the subjects can detect a change of 0.3 Hz in a constant F0 contour when F0 = 120 Hz, but the JND is an order of magnitude larger (2.0 Hz) when the F0 contour is a linear descending ramp (32 Hz/sec). Sensitivity to rate of change of F0 in linear ramps is surprisingly good; greatest sensitivity occurs when one ramp increases and the other decreases (JND = 12 Hz/sec). High‐pass filtering of the stimuli improves performance slightly, suggesting that the fundamental component is not involved in the detection of changes in F0. Substitution of the synthetic stimulus /ya/ with its dynamic formant contours in place of /ɛ/ degrades performance...

Scattering and emission of a quantum system in a strong electromagnetic wave

Abstract: A method is considered for consistent analysis of a quantum-mechanical system situated in a potential that depends periodically on the time, for example, in the field of a strong classical electromagnetic wave The emission of such a system is considered, and particularly the shift of the fundamental frequency ω' and the appearance of satellites ω' ± hω

Optimum design of vibrating cantilevers

Abstract: We determine the optimum tapering of a cantilever carrying an end mass, i.e., the shape which, for a given total mass, yields the highest possible value of the first fundamental frequency of harmonic bending vibrations in the vertical plane.

Directive harmonic generation in the radiation field of a circular piston

Abstract: An experimental and theoretical investigation is presented of farfield distortion of a finite‐amplitude wave generated by a circular‐piston source. Nearfield distortion is neglected. Thus the boundary condition is that the acoustic signal at the beginning of the farfield is a pure sine wave of amplitude proportional to the small‐signal directivity factor for the piston. The method of applying weak‐shock theory to obtain directivity patterns and propagation curves is outlined. A criterion for the maximum range at which weak‐shock theory is valid is derived for each harmonic. An ad hoc method of matching at this range the small‐signal solution, with absorption included, to the weak‐shock solution is proposed. Data obtained for a fundamental frequency of 450 kHz and source levels of 109 and 127 dB (re 1 μbar at 1 yd) are presented. Theoretical and experimental beam patterns are in good agreement. Propagation data presented for the 127‐dB source level are in poor agreement with the predictions of unmodified w...

Effect of support flexibility on the fundamental frequency of vibrating beams

Abstract: The effect of rotational and translational support flexibility on the fundamental frequency of both an almost-clamped-clamped beam and a flexibly supported cantilever beam is considered. In each case the effect of a rotationally flexible support becomes more pronounced for decreasing values of the length-to-depth ratio. It is shown that the effect of end-fixity on the fundamental frequency can be of a magnitude equal to or greater than that due to the effect of shear deformation or rotatory inertia. Results using Bernoulli-Euler beam theory and Timoshenko beam theory are compared. Expressions are formulated that give the fundamental frequency as a function of the support flexibility, length to depth ratio and fundamental frequency for a rigid support.

Method and apparatus for transmitting and receiving electrical speech signals transmitted in ciphered or coded form

Abstract: A method of, and apparatus for, transmitting and receiving electrical speech signals transmitted in ciphered form, wherein at the transmitter end there are formed in sections or intervals from the speech signals to be transmitted, by frequency analysis, signal components or parameter signals containing frequency spectrum-, voiced/voiceless information- and fundamental sound pitch coefficients, these signal components are ciphered, the ciphered signal components or parameter signals are transformed into a transmission signal and this transmission signal is transmitted over a transmission channel, and at the receiver end there is reobtained from the transmission signal the ciphered signal components or parameter signals and deciphered, and from the thus-obtained deciphered signal components or parameter signals there is generated by synthesis a speech signal which is similar to the original speech signal. According to the invention there is employed at the transmitter end for the synthesis of the transmission signal harmonic frequencies of a common fundamental frequency with constant fundamental period at least for each signal section or signal interval, the amplitudes of the individual harmonic frequencies are determined by means of the ciphered signal components or parameter signals, and from the received transmission signal by frequency analysis over at least a respective one full fundamental period there is reobtained the fundamental frequency of the ciphered parameter signals or signal components in intervals or sections. Further, for the receiver end synthesis of the speech which is similar to the original speech signal there are employed harmonic frequencies of a common fundamental frequency and such frequencies are individually modulated by the deciphered parameters signals or signal components, and the transmitter end-frequency analysis of the speech signal and the receiver end-frequency analysis of the transmission signal is carrier out by means of individually accessible harmonic frequencies of a respective common fundamental frequency.

Anharmonic overtone generation in a computor organ

Abstract: The production of musical notes containing anharmonic overtones is implemented in a computor organ of the type disclosed in U.S. patent application Ser. No. 225,883, filed Feb. 14, 1972, and now U.S. Pat. 3,809,786. In such an instrument, the sampled amplitudes of a musical waveshape are computed in real time by individually calculating the amplitude contributions of the Fourier components constituting the waveshape. In accordance with the present invention, certain of these Fourier components are evaluated at frequencies offset from multiples of the nominal fundamental frequency of the note being generated. This is accomplished by utilizing in the overtone amplitude calculations offset values Eta which establish the extent of anharmonicity of each overtone. This results in complete freedom of control of the anharmonicity of individual overtones. The overtone offset ( Eta ) values may be stored in a memory, or may be generated by appropriate circuitry. In certain embodiments the offset is proportional to the frequency of the note being produced, preferably being a constant number of cents. Other embodiments include, among other things, constant frequency offset independent of time, time variant anharmonicity, offset of alternate overtones in opposite frequency directions, and overtone selection to insure correct frequency of a subjective fundamental.

Signal recovery system for vortex type flowmeter

Abstract: A signal recovery system coupled to the sensor of a vortex-type flowmeter wherein fluidic variations are induced whose frequency is a function of the flow rate of the fluid. The sensor yields an electrical signal containing a fundamental frequency proportional to the fluidic variations as well as frequency components or noise arising from turbulence in the fluid admitted into the flowmeter. The recovery system includes a voltage-controlled band-pass filter coupled to the sensor to transmit only those frequencies which lie within a narrow range whose center frequency is determined by the applied control voltage and to discriminate against all other frequencies. In order to recover the fundamental frequency from the sensor output and to reject frequencies reflecting hydraulic noise, a control voltage is generated whose level is a function of the existing velocity of the fluid passing through the meter, the control voltage being applied to the filter to adjust the band-pass setting thereof so that the center frequency substantially corresponds to the fundamental frequency in the sensor output. The output of the filter is applied to a Schmitt trigger to provide a square wave whose frequency corresponds to the fundamental frequency, the output of the trigger being indicated to afford a reading of flow rate.

On optimal design of vibrating structures

Abstract: Optimal design problems of linearly elastic vibrating structural members have been formulated in two ways. One is to minimize the total mass holding the frequency fixed; the other is to maximize the fundamental frequency holding the total mass fixed. Generally, these two formulations are equivalent and lead to the same solution. It is shown in this work that the equivalence is lost when the design variable (the specific stiffness) appears linearly in Rayleigh's quotient and when there is no nonstructural mass. The maximum-frequency formulation then is a normal Lagrange problem, whereas the minimum-mass problem is abnormal. The lack of recognition of this can lead to incorrect conclusions, particularly concerning existence of solutions. It is shown that existence depends directly on the boundary conditions and, when a sandwich beam has a free end, a solution to the maximum-frequency problem does not exist.

Digital tone signal generator

Abstract: Counter circuits respond to depressed switches to generate two digital counts equivalent to audio frequency signals represented by a depressed switch. Digital output signals generated from the counts comprise substantially the fundamental frequency components of the desired audio frequency signals. The outputs are summed and processed to a transmission line.

AMDF Pitch Extractor

Abstract: A method is described for estimating the fundamental frequency component of voiced speech using the Average Magnitude Difference Function (AMDF). The technique, a variation of autocorrelation analysis, uses a difference signal formed by delaying the input speech various amounts and subtracting the delayed waveform from the original. The difference signal is always zero at delay = o, and exhibits deep nulls at delays corresponding to the pitch period for a voiced sound having a quasi‐periodic structure. Unlike the generation of the autocorrelation function, the AMDF calculations require no multiplications, a desirable property for real‐time speech processing. Also, since the computations involve numerous repetitive operations, they are very suitable for fabrication in special‐purpose hardware. The implementation of the AMDF pitch extractor will be described and experimental results presented to illustrate the basic measurement properties.

Integrating analog to digital converter with variable time base

Abstract: A dual slope analog to digital converter is disclosed wherein unwanted alternating signals of a fundamental frequency and integer harmonics thereof which may be superimposed on the signal to be converted are rejected by separately introducing a signal of the fundamental frequency as an additional converter input, sensing its period and precisely integrating the analog input signal for said period. The converter remains in adjustment during periods of quescence; and is so structured that its performance is not affected by the absence of the introduced separate fundamental frequency signal, or by large magnitude transient excursions of the frequency of said unwanted signal.

Paired nonlinear active elements in a waveguide cavity adapted to support orthogonal te mode waves and te mode waves

Abstract: A pair of nonlinear semiconductive active devices are located in a cavity dimensioned to support electromagnetic waves at the desired fundamental frequency in the TE10 mode. The cavity is further dimensioned to support electromagnetic waves in the TE01 mode at the second harmonic of the fundamental frequency. Coupling irises are arranged to couple out of the cavity either the TE10 mode waves or the TE01 mode waves.

Automatic pulse phase shifter for A.C.-D.C. or D.C.-A.C. converter

Abstract: An automatic pulse phase shifter in which a voltage-controlled oscillator having a fundamental frequency six times the frequency of a synchronous power supply of a converter, such as a rectifier and an inverter, is used to produce pulses with precise 60* intervals independent of the phase displacement or frequency variations due to voltage variations or disturbances in the synchronous power supply, which pulses are phase-shifted in accordance with a predetermined control signal.

Pulse eddy current testing apparatus using pulses having a 25% duty cycle with gating at pulse edges

Abstract: Pulses having a pulse width equal to one-quarter wavelength at a multiple (including 1) of the fundamental frequency of the pulses are applied to the test coil assembly of a pulse eddy current testing apparatus, and the output signals are supplied to an amplifier tuned to said multiple of the fundamental frequency. The output of the amplifier is supplied to a pair of phase-sensitive detectors which are gated at the leading and trailing edges of the applied pulses to produce quadrature signal components. These components are utilized to produce indications of defects or flaws in the object under test. The test coil assembly is advantageously designed to produce an approximately null output in the absence of defects or flaws. The pulses may have a 25 percent duty cycle with the amplifier tuned to the PRF thereof.

Maintaining desired speed of cutting tool in numerically controlled machine tool

Abstract: In a numerically controlled machine tool in which a fundamental pulse frequency determines speed of cutting tool motion along an axis, and pulses are distributed to axes according to programmed direction of cutting tool movement, successive pulses are counted into successive equal groups, each containing a number of pulses which is a multiple of the number of axes. The number of possible pulse distributions in a group is limited; hence an augmenting pulse frequency can be precomputed for each possible distribution, based on a relationship between total stairstep motion distance signified by pulses of the group and corresponding direct distance. For each group, pulses of the proper augmenting frequency are injected between pulses of the fundamental frequency so that for a given fundamental frequency speed in the same in any direction.

Signal conversion apparatus

Abstract: Identification of complex signals such as a specific phoneme spoken by different speakers is accomplished by analyzing and normalizing the spoken phoneme''s group of frequencies (formants) to a standard group, while maintaining the original harmonicratio information as channel number differences. A set of filters followed by rectifiers, to an electronic switching matrix, shifts the original filter output set through sequential sets of channels until the fundamental frequency at some input channel activates the lowest numbered ouput channel.

Fundamental‐frequency component of a finite‐amplitude plane wave

Abstract: A method due to Westervelt [Proceedings of the Third International Congress on Acoustics, Stuttgart 1959 (Elsevier, Amsterdam, 1961), Vol. 1, pp. 316–321] is used to describe the fundamental frequency component of an initially sinusoidal finite‐amplitude plane wave. The result, expressed in terms of the extra loss (in decibels) introduced by nonlinearity, is given as 10 log10[1 + Γ2(1 − e−2σ/Γ)2/16] where Γ is the acoustic Reynold's number and σ is range normalized to the shock formation distance. This relation is shown to lie within 1 dB of Blackstock's results obtained from Burgers' equation [D. T. Blackstock, J. Acoust. Soc. Am. 36, 534–542 (1964)].

Centralized controlling apparatus having control frequencies

Abstract: A centralized controlling apparatus is provided and includes a pair of frequency relays which are selectively responsive to two types of frequency signals, the same being different from a fundamental frequency and higher harmonics thereof. One of the two types of frequency signals is used as an opening signal and the other is used as a closing signal. The two types of frequency signals are respectively applied along with a fundamental frequency to a distribution or transmission line for a predetermined period of time such that two driving elements of a differential type relay are selectively operated in accordance with the switching of the frequency relays such that a main circuit to a load is either opened or closed.

Tone generating system

Abstract: A system for generating sustained pulse trains having frequencies related to the fundamental frequency of a controlling input signal includes means for extracting the fundamental frequency of the input, a first register for accumulating a count related to this fundamental frequency, a second register for repeatedly producing an output at selectable rates which are related to the accumulated count and divider circuits for producing various ratios of the output. The accumulated count can be adjusted to compensate for deviations of the input frequency from a desired scale.

The effect of fundamental frequency variations on the perception of stress in German.

Abstract: An analysis of fundamental frequency variations occurring with stressed syllables in a sample of natural German speech is used to examine some of the results obtained by Isacenko and Schadlich from experiments with synthesized speech. Isacenko and Schadlich’s results indicated that perceptible rises and falls in fundamental frequency can lead to the perception of stress. The present analysis indicates that not all syllables with which perceptible fundamental frequency variations occur are heard as stressed; but it is possible that the last change in pitch direction in an ‘information unit’ leads to the perception of stress on the syllable with which the change is associated.

The origin of the heart sounds

Abstract: Applying mathematical frequency analysis to phonocardiographic records the author could show that: 1. heart sounds are not composed of noises of short duration, as supposed hitherto, but consist of short complexes comprising a fundamental frequency and wholefigured upper partials; 2. the harmonic upper partials of first heart sound, second heart sound, and mitral opening snap have common zero-crossing points with the fundamental frequency, which means that there is phase balance between fundamental frequency and hormonics; 3. because of statements 1 and 2 one can conclude that spheric sound emitters are the sources of heart sounds; 4. a proposed vibration model is in aggreement with the statements 1 to 3. A vibration equation is derived from this model; 5. there is a strong correlation between the fundamental frequency of the first part of first heart sound and heart volume as well as between the fundamental frequency of mitral opening snap and volume of the left atrium; 6. variation in size of the left ventricle causes corresponding variations of the fundamental frequency of the first part of first heart sound; 7. in patients with mitral stenosis and atrial fibrillation it seems possible to evaluate the degree of stenosis by the variation of the fundamental frequency of the first heart sound; 8. the membranes of the heart valves are not the sources of heart sounds; 9. there was no evidence for the existence of a so called “pure muscle tone”.

A Theory on the Characteristics of Pitch and Formant Frequency Transitions in Human Speech

Abstract: Perceptual experiments have shown that the characteristics of fundamental frequency (pitch) and formant frequency variations usually represent a more important acoustic cue than those of the formant amplitudes. Unfortunately, however, the exact nature of these frequency transitions is far more subtle. If the speech production process is viewed as a closed‐loop feedback control system, application of modern control theory techniques yields a rather interesting model for the vocal‐tract control function. This system may be viewed in terms of the familiar phase‐locked loop. The loop filter model, which appears to fit both theoretical considerations and the empirical (sound spectrograph) results, is the so‐called “imperfect integrator,” with transfer function F(s) = (s+a)/(s+b). A discussion of this proposed model, including samples of synthetic speech, is presented.