Showing papers on "Fundamental frequency published in 1987"

Digital speech vocoder

Abstract: A speech analyzer and synthesizer system using a sinusoidal encoding and decoding techniques for voiced frames and noise excitation or multiple pulse excitation for unvoiced frames. For voiced frames, the analyser (100) transmits the pitch, values for each harmonic frequency by defining the offset from integer multiples of the fundamental frequency, total frame energy, and linear predictive coding, LPC, coefficients (FIG. 1). The synthesizer (200) is responsive to that information to determine the phase of the fundamental frequency and each harmonic based on the transmitted pitch and harmonic offset information and to determine the amplitudes of the harmonics utilizing the total frame energy and LPC coefficients (FIG. 2). Once the phase and amplitudes have been determined for the fundamental and harmonic frequencies, the sinusoidal analysis is performed for voiced frames. For each frame, the determined frequencies and amplitudes are defined at the center of the frame, and a linear interpolation is used both to determine continuous frequency and amplitude signals of the fundamental and the harmonics throughout the entire frame by the synthesizer. In addition, the analyzer initially adjusts the pitch so that the harmonics are evenly distributed around integer multiples of this pitch.

A spectral autocorrelation method for measurement of the fundamental frequency of noise-corrupted speech

Abstract: A method for measurement of the fundamental frequency of a voiced speech signal corrupted by high levels of additive white Gaussian noise is described. The method is based on flattening the spectrum of the signal by a bank of bandpass lifters and extracting the pitch frequency from autocorrelation functions calculated at the output of the lifters. A smoothing modified median filter is applied to the calculated pitch frequency contour to result in an improvement in the accuracy of the method. A byproduct of the pitch tracker is a voiced/ unvoiced classifier. The maximum and the variance of the autocorrelation function maxima, over the bank of lifters, serve as the basis for voiced/unvoiced classification by making use of a two-dimensional, nearest-neighbor pattern recognition approach. Results are presented for fundamental frequency measurement and voiced/unvoiced classification for several signal-to-noise ratios.

Acoustic analysis of speech variables during depression and after improvement.

Abstract: Speech recordings were made of 16 depressed patients during depression and after clinical improvement. The recordings were analyzed using a computer program which extracts acoustic parameters from the fundamental frequency contour of the voice. The percent pause time, the standard deviation of the voice fundamental frequency distribution, the standard deviation of the rate of change of the voice fundamental frequency and the average speed of voice change were found to correlate to the clinical state of the patient. The mean fundamental frequency, the total reading time and the average rate of change of the voice fundamental frequency did not differ between the depressed and the improved group. The acoustic measures were more strongly correlated to the clinical state of the patient as measured by global depression scores than to single depressive symptoms such as retardation or agitation.

Fundamental plasma emission involving ion sound waves

Abstract: The theory for fundamental plasma emission by the three-wave processes L + or - S to T (where L, S and T denote Langmuir, ion sound and transverse waves, respectively) is developed. Kinematic constraints on the characteristics and growth lengths of waves participating in the wave processes are identified. In addition the rates, path-integrated wave temperatures, and limits on the brightness temperature of the radiation are derived.

Digital speech sinusoidal vocoder with transmission of only a subset of harmonics

Abstract: A speech analyzer and synthesizer system using a sinusoidal encoding and decoding technique for voiced frames and noise excitation or multipulse excitation for unvoiced frames. For voiced frames, the analyzer transmits the pitch, values for a subset of offsets defining differences between harmonic frequencies and a fundamental frequency, total frame energy, and linear predictive coding, LPC, coefficients. The synthesizer is responsive to that information to determine the harmonic frequencies from the offset information for a subset of the harmonics and to determine the remaining harmonics from the fundamental frequency. The synthesizer then determines the phase for the fundamental frequency and harmonic frequencies and determines the amplitudes of the fundamental and harmonics using the total frame energy and the LPC coefficients. Once the phase and amplitudes have been determined for the fundamental and harmonic frequencies, the synthesizer performs a sinusoidal analysis. In another embodiment, the remaining harmonic frequencies are determined by calculating the theoretical harmonic frequencies for the remaining harmonic frequencies and grouping these theoretical frequencies into groups having the same number as the number of offsets transmitted. The offsets are then added to the corresponding theoretical harmonics of each of the groups of the remaining harmonic frequencies to generate the remaining harmonic frequencies. In a third embodiment, the offset signals are randomly permuted before being added to the groups of theoretical frequencies to generate the remaining harmonic frequencies.

Harmonic distortion in PWM inverter output waveforms

Abstract: It is usual to provide a short “dead time” between switching one device in an inverter leg off and switching the other device on, to prevent them conducting simultaneously. It is known that this expedient modifies the harmonic content of the output voltage waveform of a pulse-width modulation (PWM) inverter. It changes the amplitude of the fundamental component, which can be significant in variable-speed drives when the frequency ratio is changed. It also introduces low-amplitude, low-order harmonic components which are not wanted in uninterruptible power supplies when voltage waveforms of high purity are demanded. This problem has been treated quantitatively and it has been shown by a systematic set of experiments that the proposed theoretical method is reliable. It has been found that the amplitudes of the odd harmonics produced depend only upon the ratio of the dead time to the period of the switching frequency. Similarly the amplitudes of the even harmonics, which only occur with even frequency ratios, depend on the ratio of the dead time to the period of the fundamental frequency. Accordingly it has been possible to present generalised curves which allow the design engineer to estimate the amplitudes of these harmonics for any combinations of fundamental and modulating frequencies. These results have been presented in such a way that they are applicable to both single-phase and 3-phase PWM inverters.

Radio frequency spectroscopy apparatus and method using multiple frequency waveforms

Abstract: An apparatus and method for measuring the concentration of a chemical substance in a test sample based on a technique of waveform distortion analysis is disclosed. The apparatus includes a waveform generator that generates a periodic electromagnetic signal having a plurality of frequencies simultaneously present. Preferably the signal has a fundamental frequency and simultaneously present harmonic frequencies which shape the waveform. The shaped periodic signal is transmitted through the test sample by a probe assembly which also receives the transmitted signal from the test sample. Propagation of the shaped signal through the test sample results in a change in the waveform shape or distortion by the chemical, and a detector circuit is provided that quantifies the change in shape of the signal to determine the concentration of the chemical in the test sample. The harmonics producing the waveform shape and the fundamental frequency of the signal are both selected so that the change in shape of the signal is particularly responsive to the presence of a selected chemical substance. The magnitude of the distortion or change in shape of the signal can be directly correlated to the concentration of the selected chemical substance.

One-dimensional gas flow

Abstract: This chapter discusses the steady flow of a gas in one dimension. An important class of one-dimensional nonsteady gas flows is formed by flows occurring in conditions where there are characteristic velocities but not characteristic lengths. The simplest example of such a flow is given by gas flow in a semi-infinite cylindrical pipe terminated by a piston when the piston begins to move with constant velocity. Such a flow is defined by the velocity parameter and by parameters that give the gas pressure and density at the initial instant. If the wave is purely harmonic at some instant, it ceases to be so at later instants on account of the change in shape of the profile. The motion, however, remains periodic with the same period as before. When the wave is expanded in a Fourier series, terms with frequencies nΩ, with n being integral and Ω being the fundamental frequency, appear.

Maximum Frequency Design of Symmetric Angle-ply Laminates

Abstract: This chapter considers the optimal design of classical laminates for maximum fundamental frequency. The constituent laminae are orthotropic and are stacked so that the geometry and material axis orientation are symmetric with respect to the plate’s middle surface. The design variables are the orientations of the constituent laminae. Design derivatives of the fundamental frequency are used to determine conditions both necessary and sufficient to ensure at least a local maximum for the fundamental frequency. Specific results are presented for four- and eight-ply laminates subjected to various combinations of clamped, supported and free edge boundary conditions.

Analysis of the Double Output Induction Generator Using Direct Three-phase Model Part II - Harmonic Analysis

Abstract: This paper investigates the harmonic content of the rotor current, rotor voltage and the torque of the variable speed constant frequency double output induction generator (VSCF-DOIG). The waveforms of these variables were generated using a direct three-phase model and then analyzed numerically for their harmonic content using a Fourier series subroutine. In addition, this paper investigates the stator distortion currents that are being induced in the stator windings by the rotor current harmonics at frequencies which are not an integral multiple of the stator fundamental frequency. As a check on the analysis the calculated stator current waveform is compared with the experimental oscillogram.

Simultaneous observation of fundamental and second harmonic radio emission from the terrestrial foreshock

Abstract: There have been many reports of the terrestrial foreshock as a source of freely propagating electromagnetic (em) radiation1–7, identified as plasma emission at twice the solar-wind plasma frequency, 2fp The 2fp source is close behind the curved surface defined by the interplanetary magnetic field lines tangent to the Earth's bow shock Electrons accelerated at the shock over a wide range of energies propagate along these field lines where, from a time-of-flight effect6, they have a distribution that is unstable to the production of Langmuir waves6,8 These Langmuir waves9,10 and the unstable electron distributions11,12 have been observed The mechanism suggested for generating the 2fp radiation5,6,13,14 by the terrestrial foreshock is closely related to present models of type III solar radio emission and rely on some of the energy in the Langmuir waves converting to em waves The em emission of type III bursts is known to be produced in the solar wind at both the fundamental and second harmonic15, and whether fundamental emission is produced in the terrestrial foreshock is of considerable interest Comparison of nearby fundamental and harmonic emissions and the Langmuir wave energy density in the source will help discriminate between the different conversion models8,14,16 We present here unambiguous measurements made with the sounder experiment aboard the International Sun–Earth Explorer-1 (ISEE-1) and the radio experiment on ISEE-3 of simultaneous fundamental and second harmonic em emission from the Earth's foreshock

Pseudosinusoidal oscillator drive system

Abstract: A circuit (62, 64) for receiving a periodic input signal at frequency f, and for producing a pseudosinusoidal staircase output signal at a fundamental frequency f from which predetermined harmonics of the fundamental frequency are absent. Also provided are an oscillator in which such a circuit forms the drive circuit for a piezoelectric crystal, and an accelerometer in which such an oscillator is used as the force sensing means. In the accelerometer, the reaction force of a proof mass (40) is sensed by a resonator that comprises a drive circuit (44) for producing a drive signal and a piezoelectric crystal (42) connected between the proof mass and support (46). In response to the drive signal, the crystal undergoes mechanical vibration at a frequency f that varies with the force applied to the crystal. A resonator signal corresponding to the mechanical vibration is produced and input to drive circuit. The drive circuit responds by producing the drive signal in the form of a periodic, pseudosinusoidal staircase function. The staircase function has fundamental frequency f, and has N steps of M discrete nonzero amplitude levels per period. N and M are integers greater than one, with M being less than N. The drive circuit produces the M amplitude levels such that predetermined harmonics of the fundamental frequency f are not present in the drive signal, thereby reducing the possibility of activity dips in the accelerometer output.

Perception of front vowels: the role of harmonics in the first formant region.

Abstract: Vowel matching and identification experiments were carried out to investigate the perceptual contribution of harmonics in the first formant region of synthetic front vowels. In the first experiment, listeners selected the best phonetic match from an F1 continuum, for reference stimuli in which a band of two to five adjacent harmonics of equal intensity replaced the F1 peak; F1 values of best matches were near the frequency of the highest frequency harmonic in the band. Attenuation of the highest harmonic in the band resulted in lower F1 matches. Attenuation of the lowest harmonic had no significant effects, except in the case of a 2‐harmonic band, where higher F1 matches were selected. A second experiment investigated the shifts in matched F1 resulting from an intensity increment to either one of a pair of harmonics in the F1 region. These shifts were relatively invariant over different harmonic frequencies and proportional to the fundamental frequency. A third experiment used a vowel identification task to determine phoneme boundaries on an F1 continuum. These boundaries were not substantially altered when the stimuli comprised only the two most prominent harmonics in the F1 region, or these plus either the higher or lower frequency subset of the remaining F1 harmonics. The results are consistent with an estimation procedure for the F1 peak which assigns greatest weight to the two most prominent harmonics in the first formant region.

Tuning indicator for musical instruments

Abstract: A tuning indicator is disclosed in which the octave, note within the octave, and a tuning error is displayed for a musical tone played into a microphone. A bank of digital octave filters, a bank of digital note filters, a bank of digital cent filters operate simultaneously and in parallel to analyze the fundamental frequency of the musical tone. The filters operate by computing the autocorrelation function of the input signal and then performing a Fourier transform to obtain the frequency analysis data. An efficient and simple implementation is disclosed for the computations including the analog-to-digital signal conversion, the computation of the autocorrelation function, and the Fourier transform.

Dynamic Testing under Nonsinusoidal Conditions and the Consequences of Nonlinearity for Service Performance

Abstract: In this work, nonlinearity in the dynamic behavior of rubber has been considered. In order to understand its effects in a service environment involving complex patterns of vibration, it has been necessary to clarify the derivations of dynamic properties for the sinusoidal excitation that is conventionally used in testing. Using the fundamental frequency components as a basis, non-linearity can be quantified by the harmonic components that it produces. A dynamic test system has been developed which incorporates the ability to perform a harmonic analysis, and the usefulness of this has been demonstrated. Harmonic analysis has enabled the dynamic behavior of rubber to be quantified under complex, periodic waveforms. This is necessary for filled rubbers, because their nonlinearity means that a superposition on their properties from sinusoidal tests is incorrect. Examples of this approach for assessing dynamic behavior range from shock mounts to tire treads. Dual-sine tests on a nonlinear rubber indic...

Distance Measurement Using a Pulse Train Emitted from a Laser Diode

Abstract: A distance meter has been developed using a pulse train emitted from a laser diode. The frequency spectrum of the pulse train consists of the fundamental frequency and its harmonics of the modulation current supplied to the laser diode. The interference effect between the detected signal and the field leakage, induced by the modulation current, was removed through the heterodyne detection of the second harmonic, and the systematic error caused from this interference effect was decreased in phase measurements. The precision of the distance measurement was improved, especially when the detected light signal was very weak.

Crystal controlled transmitter

Abstract: A short distance, battery powered, amplitude modulated, crystal controlled RF transmitter for transmitting encoded security information. In its preferred embodiments, the transmitter comprises a novel fifth overtone crystal oscillator which self-produces a carrier frequency at the third harmonic of the fifth overtone of the crystal's fundamental frequency, which carrier frequency is coupled by a series resonant trap, or a pi network, tuned to the carrier frequency to an amplifier stage where the carrier is amplitude modulated via pulse position encoded binary security data. In an alternative embodiment, the transmitter comprises matched crystal oscillator, tripler and amplifier stages. Also disclosed is an antenna including a battery clip contact.

Attenuation of intense sinusoidal waves in air-saturated, bulk porous materials

Abstract: As intense, initially sinusoidal waves propagate in fluids, shocks form and excess attenuation of the wave occurs. We present data indicating that shock formation is not necessary for the occurrence of excess attenuation in nonlinear, lossy media, i.e., air‐saturated, porous materials. An empirical equation is used to describe the excess attenuation of intense sinusoids in porous materials. The acoustic nonlinearity of and the excess attenuation in porous materials may be predicted directly from dc flow resistivity data. An empirical relationship is used to relate an acoustic nonlinearity parameter to the fundamental frequency and relative dc nonlinearity of two structurally different materials.

Hand-held power system harmonic distortion meter with selective activation of display

Abstract: A hand-held, battery-powered harmonic distortion meter reduces the level of the AC power waveform of interest to a level compatible with the measurements to be performed, converts successive portions of the reduced waveform to digital representations in a multi-bit format for processing, stores a predetermined number of sequences of the digital representations, processes the stored sequences according to a fast Fourier transform algorithm using time decomposition with input bit reversal to produce intermediate calculations of the real and imaginary parts of the DC, fundamental frequency and harmonic components of the input waveform, further processes the intermediate calculations to obtain various parameters of the input waveform including magnitude of the harmonic components as a percentage of the fundamental frequency of the waveform, and selectively displays the final calculations according to switch selections on the face of the meter.

Selective code reader

Abstract: A selective bar code reader distinguishes code data from other data obtained from a carrier before reading the data. The selective bar code reader comprises a scanner (23) for generat­ ing electrical signals having a first portion representing the code and a second portion representing other regions on the carrier, a processor (50) for generating an electrical waveform having a first portion corresponding to the first portion of the electrical signals and having a fundamental frequency corre­ sponding to the spacing between the bar code elements and a second portion corresponding to the second portion of the electrical signals and not having a fundamental frequency cor­ responding to the spacing between the elements of the bar code. The electrical waveform is passed through a band pass filter (100) centered at the fundamental frequency to attentu­ ate the second portion of the electrical waveform and thereby identify the first portion of the electrical waveform and the bar code data.

ML estimation of the fundamental frequency of a harmonic series

Abstract: A Maximum Likelihood (ML) estimator is developed for the fundamental frequency of a harmonic family of sinusoidal tones. The estimator is implemented using an extension of the Generalised Phase Interpolation Estimator (GPIE). The Cramer-Rao bound for the variance of the estimator is presented for the case of a harmonic series embedded in white, Gaussian noise. The method is tested by its application to simulated data, and an example of the application of the technique to real acoustic data is also presented.

Optical inspection device and method

Abstract: A closed loop optical gauge directs a laser beam toward an object whose radial velocity, instantaneous position, and/or shape are to be measured, and utilizes the Doppler frequency shift of the reflected beam to make measurements. A reference sample of the original direct beam has its frequency shifted by an acoustooptical modulator. A closed loop system is created by sensing the difference in frequency between the reflected beam and the shifted reference beam. The amount of frequency modulation is then controlled so that the frequency of the shifted reference beam continuouly tracks that of the reflected beam, preferably with a fixed offset of frequency. The output can be integrated with respect to time to obtain position or shape information. Absolute distance to the object is measured by transmitting a train of pulses of light toward the object and receiving reflected light pulses back. The round trip time of the light pulses is ascertained by measuring the phase displacement of the envelope of the reflected signals relative to the envelope of the transmitted light signals, with the aid of a phase locked loop. The oscillator of the phase locked loop is locked to the envelope of a reference sample of the transmitted signal, and can operate selectively at the fundamental frequency or a higher harmonic frequency of that envelope. A selected harmonic from the oscillator can be compared as to phase with the corresponding harmonic of the reflected light pulses. With calibration, the system can measure flight time, and therefore distance to the object, with high resolving power at the higher harmonic frequencies.

Harmonic and transient scattering from weakly nonlinear objects

Abstract: A mathematical model for scattering of electromagnetic waves from weakly nonlinear objects is developed. The constitutive relations are based on Volterra series, but additional, physically plausible, heuristic assumptions have to be introduced in order to solve the scattering problem. The general theory is discussed in connection with scattering from circular cylinders. These canonical problems demonstrate the new phenomena involved. It is shown that the first order effects of the nonlinear scattering problem involve modification of the linear scattering coefficients and production of new multipole terms at the fundamental frequency. In addition, part of the energy is transformed into harmonics. The corresponding problem of transient scattering is considered. The new effects of pole migration and pole creation are discussed. The present study contributes to understanding the theoretical aspects of nonlinear scattering, and may also provide a method for remote sensing of nonlinear targets.

Vibrating beam partially embedded in Winkler-type foundation

Abstract: The fundamental frequency of transverse vibration of a beam with intermediate supports and partially embedded in a Winkler-type foundation is determined using the Rayleigh-Schmidt approach. The displacement function is approximated using polynomials that contain an exponential optimization parameter.

Psychophysics of Audio Signal Processing and the Role of Pitch in Speech

Abstract: This paper is going to describe a broad and general approach to a problem which at first sight may appear relatively special, namely, the psychoacoustic representation of the first two vowel formants. The problem emerges from two facts, the first of which is pertinent to the speech source, the second to the auditory receiver: (1) the relatively high oscillation frequency of the vocal cords (“voice fundamental frequency”) which renders the physical representation of vocal-tract resonances quite scanty; (2) the auditory system’s relatively high frequency selectivity, which in the lower frequency region analyses the signal into individual harmonics rather than formants. An illustration is given in Fig. 1, showing schematically the boundary separating the area of auditory analysis into spectral pitches of individual harmonics from that of melted perception (It should be noted that actually there is not a sharp boundary but a transient zone that depends on the vowel’s spectral envelope and SPL; cf. Plomp & Mimpen, 1968; Terhardt, 1979a,b; Stoll, 1982; Houtgast, 1974). It is apparent that in practically the whole oscillation-frequency range typical of natural speech resolution into individual harmonics takes place in the existence region of the first two formants.