Showing papers on "Fundamental frequency published in 1992"

Modeling the identification of concurrent vowels with different fundamental frequencies.

Abstract: Human listeners are better able to identify two simultaneous vowels if the fundamental frequencies of the vowels are different. A computational model is presented which, for the first time, is able to simulate this phenomenon at least qualitatively. The first stage of the model is based upon a bank of bandpass filters and inner hair‐cell simulators that simulate approximately the most relevant characteristics of the human auditory periphery. The output of each filter/hair‐cell channel is then autocorrelated to extract pitch and timbre information. The pooled autocorrelation function (ACF) based on all channels is used to derive a pitch estimate for one of the component vowels from a signal composed of two vowels. Individual channel ACFs showing a pitch peak at this value are combined and used to identify the first vowel using a template matching procedure. The ACFs in the remaining channels are then combined and used to identify the second vowel. Model recognition performance shows a rapid improvement in ...

Control of Along-Wind Response of Structures by Mass and Liquid Dampers

Abstract: An investigation is made of the possible application of tuned liquid column dampers and tuned liquid column/mass dampers in reducing the along-wind response of wind-sensitive structures. The structure is modeled as a lumped mass multi-degree-of-freedom system taking into account both bending and shear. The wind turbulence is modeled as a stochastic process that is stationary in time and nonhomogeneous in space. A random vibration analysis utilizing transfer matrix formulation is carried out to obtain response statistics. The nonlinear damping term in the fundamental equation of the tuned liquid damper is treated by an equivalent linearization technique. Numerical examples show that tuned liquid dampers, which have significant practical advantages, are as effective as the traditional tuned mass dampers if the parameters of the liquid dampers are properly selected. However, excessive liquid motion in a tuned liquid column/mass damper may reduce the effectiveness of this damper. It is also shown that the wind-induced force- and acceleration-type responses of the structure with a damper, which is usually tuned to the fundamental frequency of the structure, should involve more than one vibration mode as higher-mode responses may become as large or even larger than the controlled-mode response.

Musical fundamental frequency tracking using a pattern recognition method

Abstract: In a recent article [J C Brown, ‘‘Calculation of a Constant Q Spectral Transform,’’ J Acoust Soc Am 89, 425–434 (1991)], the calculation of a constant Q spectral transform that gives a constant pattern in the log frequency domain for sounds with harmonic frequency components has been described This property has been utilized in calculating the cross‐correlation function of spectra of sounds produced by musical instruments with the ideal pattern, which consists of one’s at the positions of harmonic frequency components Therefore, the position of the best approximation to the ‘‘ideal’’ pattern for the spectra produced by these instruments has been determined, and in so doing the fundamental frequency for that sound has been obtained Results are presented for scales produced by the piano, flute, and violin as well as for arpeggios played by a wide variety of instruments

High-accuracy Fourier analysis based on synchronous sampling techniques

Abstract: The lack of synchronization between the sampling rate and the signal frequency represents the main source of errors in the frequency analysis of periodic signals performed by means of digital techniques. Several algorithms have been proposed in the literature to reduce these errors, at the cost of an increment in the computational burden imposed by the instrument. The complete elimination of these errors can be achieved only when the sampling rate is synchronized to the fundamental frequency of the signal to be analyzed. It is shown how this can be attained, and the results of fast Fourier transforms (FFTs) performed on multifrequency signals under synchronous sampling conditions are indicated. The accuracy of these measurements is discussed. >

A periodic second harmonic spatial power combining oscillator

Abstract: The authors present a periodic second-harmonic spatial power combining oscillator. The power combining is achieved by phase locking the oscillators at the fundamental frequency and combining the second-harmonic power in space through an array of microstrip patch antennas. The effect of moding and multiple device-circuit interaction is investigated. This circuit is planar, and therefore simplifies the design of monolithic circuits, X-band Gunn diodes are used for the purpose of demonstration. >

On the acoustics of tuning forks

Abstract: Tuning forks can vibrate in many different modes in which the tines move either in the plane or perpendicular to the plane of the fork. Symmetrical modes can be modeled by the motion of two cantilever beams, antisymmetrical modes by the motion of a beam with free ends. A tuning fork vibrating in its fundamental mode is approximately a linear quadrupole sound source whose strength can be increased by use of a baffle or by touching the stem to a soundboard. The motion of the stem includes strong components at both the fundamental frequency and its second harmonic. Slight alterations in a tuning fork can enhance or suppress either of these components. At large amplitudes, the tines vibrate nonsinusoidally, the nth harmonic increasing approximately as the nth power of the fundamental.

Fundamental frequency and period detector

Abstract: Fundamental frequency and period detector processes and systems which determine the end of a cycle of an ac waveform by using the characteristic of the integral of a single cycle of an ac waveform that the value of the integral at the end of the cycle is the same as at the cycle start despite cycle noise, multiple zero crossings and other cycle obscuration. These processes and systems use the cycle integral to self-synchronize with each cycle of an ac waveform. Formation of the cycle integral of each processed cycle is a useful by-product of the frequency and period detection processes and systems.

Accurate on-wafer power and harmonic measurements of MM-wave amplifiers and devices

Abstract: A novel integrated test system that accurately measures on-wafer S-parameters, power levels, load-pull contours and harmonics over 1 to 50 GHz is presented. The system measures power and S-parameters with single contact measurements and integrated hardware. There are two keys to this system: first, the network analyzer samplers are used as frequency-selective power meters with large dynamic ranges; second, all measurements are vector-corrected to the device under test reference planes. The capabilities and accuracy were demonstrated by measuring the power at the fundamental frequency and four harmonic frequencies of a 50-GHz traveling wave amplifier and the load-pull contours of a MODFET at 30 GHz. >

System and method for acquiring an optical target

Abstract: An optical target is acquired by an optical scanning system according to an in-band target frequency in an input signal from an optical scanning device. Both the in-band energy level and the out-of-band energy level of the input signal from the optical scanning device are determined. These two energy levels are compared and a possible detection of the target is determined according to this comparison. A minimum threshold of in-band energy is required in order for the possible detection to be confirmed. The input signal may have various frequencies due to various amounts of magnification of the acquisition target as scanned by the optical scanning device. Thus the input signal may represent the target as various frequencies due to the various amounts of magnification. The various amounts of magnification of the acquisition target are due to various scanning distances between the scanning device and the acquisition target. Magnification compensation is therefore performed by providing an amount of frequency shifting of either the center frequency of a filter or the input signal frequency. The amount of frequency shifting is determined according to scanning distance. The frequency shifting is accomplished by performing digital-to-analog conversion on the digital input signal at a fiexed frequency. The output of the digital-to-analog converter is applied to an analog-to-digital converter where the analog signal is resampled at a varying resampling frequency. When the resampling frequency differs from the sampling frequency the signal is frequency shifted. Alternately, the resampled signal may be buffered and clocked out, in which case the frequency of the input signal is effectively shifted. In order to vary the amount of frequency shift according to the scanning distance, the resampling frequency applied to the analog-to-digital converter is varied according to the scanning distance. The relationship between the various resampling frequency and the varying scanning distances may be selected to cause the various input frequencies representative of a scanned acquisition target to be shifted to a single predetermined fundamental frequency.

Speech information extractor

Abstract: A method and apparatus for extracting information from human speech are disclosed. A speech signal is received into a bank of bandpass filters and the instantaneous amplitude modulation and frequency modulation of each harmonic in the speech waveform is determined. A logarithm of the instantaneous frequency of the speech fundamental frequency is determined, for example, by computing a weighted average of the frequency modulations of the harmonics. An output signal is formed having the logarithm of the frequency of the thus determined speech fundamental and the logarithms of the amplitude modulation for the ten lowest frequency speech harmonics and/or the speech envelope.

Harmonic-adjusted watt-hour meter

Abstract: An electric power measuring system wherein the watt-hour measurements are adjusted to account for the economic effects of harmonic currents and voltages. Well known techniques are used to acquire frequency spectra that represent the voltages and currents present at the measuring point. These spectra are used to calculate power flow direction and magnitude at various frequencies. Weighting functions are applied to power flows at frequencies other than the fundamental frequency. The weighted power flow is used to calculate an harmonic-adjusted watt measurement, which is then accumulated to form a harmonic-adjusted watt-hour measurement. The weighting functions can be selected to provide an economic incentive for a power consumer to consume power in a way that matches the goals of the power provider.

Time normalization in voice analysis.

Abstract: The harmonics‐to‐noise ratio (HNR) has been widely accepted for quantifying the irregular or noise component of voice. HNR, however, is usually inflated by cycle‐to‐cycle variations of fundamental frequency period because zero padding is used for time normalization of the wavelet. In this study, a new method was developed for analyzing waveform perturbations of voice. In this method, noise components of voice were calculated from the discrepancies between wavelets after they had been optimally aligned in time. The optimal time normalization of wavelets was accomplished using procedures of dynamic time warping (DTW). This method was evaluated using both synthetic and natural voices, and significant reductions in noise were obtained. The harmonics‐to‐noise ratio obtained using DTW for time normalization was also shown to be independent of fundamental frequency perturbations.

Pitch related to spectral edges of broadband signals.

Abstract: A complex tone often evokes a pitch sensation associated with its extreme spectral components, besides the holistic pitch associated with its fundamental frequency. We studied the edge pitch created at the upper spectral edge of complexes with a low-pass spectrum by asking subjects to adjust the frequency of a sinusoidal comparison tone to the perceived pitch. Measurements were performed for different values of the fundamental frequency and of the upper frequency of the complex as well as for three different phase relations of the harmonic components. For a wide range of these parameters the subjects could adjust the comparison tone with a high accuracy, measured as the standard deviation of repeated adjustments, to a frequency close to the nominal edge frequency. The detailed dependence of the matching accuracy on temporal parameters of the harmonic complexes suggests that the perception of the edge pitch in harmonic signals is related to the temporal resolution of the hearing system. This resolution depends primarily on the time constants of basilar-membrane filters and on additional limitations due to neuronal processes.

A scheme for pitch extraction of speech using autocorrelation function with frame length proportional to the time lag

Abstract: Although pitch extraction schemes based on the short-time autocorrelation function offer reliable results for most of the speech signal, the autocorrelation peaks indicating fundamental period fluctuate with frame position, causing occasional pitch extraction errors. In order to reduce these errors, a scheme using a new definition of normalized short-time autocorrelation function is proposed. One of the major advantages of the definition over conventional ones is that the frame length changes in proportion to the time lag, and, therefore, the input speech can be analyzed without any knowledge of the fundamental frequency range of the speaker. Two methods are proposed for the normalization, and the one compensating for variations of the short-time power of the waveform is shown to offer better results. A system for pitch extraction is constructed on a workstation, and the validity of the proposed scheme is demonstrated by experiments using the connected speech of male and female announcers. >

Apparatus and method for qualitative and quantitative measurements of optical properties of turbid media using frequency-domain photon migration

Abstract: Optical measurements of turbid media, that is media characterized by multiple light scattering, is provided through an apparatus and method for exposing a sample to a modulated laser beam. The light beam is modulated at a fundamental frequency and at a plurality of integer harmonics thereof. Modulated light is returned from the sample and preferentially detected at cross frequencies at frequencies slightly higher than the fundamental frequency and at integer harmonics of the same. The received radiance at the beat or cross frequencies is compared against a reference signal to provide a measure of the phase lag of the radiance and modulation ratio relative to a reference beam. The phase and modulation amplitude are then provided as a frequency spectrum by an array processor to which a computer applies a complete curve fit in the case of highly scattering samples or a linear curve fit below a predetermined frequency in the case of highly absorptive samples. The curve fit in any case is determined by the absorption and scattering coefficients together with a concentration of the active substance in the sample. Therefore, the curve fitting to the frequency spectrum can be used both for qualitative and quantitative analysis of substances in the sample even though the sample is highly turbid.

Device for attenuating the periodic vibrations of a mechanical structure

Abstract: A device for attenuating the periodic vibrations of a mechanical structure adapted to obtain cancellation of periodic vibrations of rotating machines including at least one transducer, detecting original vibrations, delivering a detected signal, a detector of the periodicity of these vibrations delivering a synchronizing signal, and a control circuit and a transducer generating compensation vibrations which are applied to the mechanical structure. The control circuit includes a circuit for synchronous filtering of the detected signal, controlled by the synchronizing signal and delivering a filtered signal whose frequency spectrum contains only the instaneous fundamental frequency of the detected signal. A circuit for regulating the filtered signal delivers an antivibration-control signal applied to a generating transducer in order to minimize the amplitude of the detected signal.

Fundamental Frequency of Tapered Plates by Differential Quadrature

Abstract: In this paper, a differential quadrature method is presented for computation of the fundamental frequency of a thin rectangular isotropic elastic plate with variable thickness. In this method, a partial derivative of a function with respect to a space variable at a discrete point is approximated as a weighted linear sum of the function values at all discrete points in the region of that variable. The weighting coefficients are treated as the unknowns. Applying this concept to each partial derivative of the free vibration differential equation of motion of the plate gives a set of linear simultaneous equations, which are solved for the unknown weightage coefficients by accounting for the boundary conditions. The method is used to evaluate the fundamental frequency of linearly tapered plates with simply supported, fully clamped, and mixed boundary conditions. Results are compared with existing solutions available from other analytical and numerical methods. The method presented gives accurate results and is...

Auditory nerve representation of a complex communication sound in background noise.

Abstract: A population study of auditory nerve responses in the bullfrog, Rana catesbeiana, analyzed the relative contributions of spectral and temporal coding in representing a complex, species‐specific communication signal at different stimulus intensities and in the presence of background noise. At stimulus levels of 70 and 80 dB SPL, levels which approximate that received during communication in the natural environment, average rate profiles plotted over fiber characteristic frequency do not reflect the detailed spectral fine structure of the synthetic call. Rate profiles do not change significantly in the presence of background noise. In ambient (no noise) and low noise conditions, both amphibian papilla and basilar papilla fibers phase lock strongly to the waveform periodicity (fundamental frequency) of the synthetic advertisement call. The higher harmonic spectral fine structure of the synthetic call is not accurately reflected in the timing of fiber firing, because firing is ‘‘captured’’ by the fundamental ...

The role of interaural time difference and fundamental frequency difference in the identification of concurrent vowel pairs

Abstract: The ability of subjects to identify both components of a concurrent vowel pair was determined when vowel fundamental frequency difference and an interaural time difference (ITD) in one of the vowels were introduced. In agreement with earlier studies it was found that introduction of a fundamental frequency difference significantly improved detection performance (by 22% for a 1 semitone difference). Identification performance improved as the ITD was made larger but this improvement was small compared to the fundamental frequency difference effect (7% improvement between 0 and 400 μs).

Harmonic-balance analysis of microwave oscillators with automatic suppression of degenerate solution

Abstract: A systematic approach to the frequency-domain analysis of autonomous microwave circuits for which the fundamental frequency of oscillation is unknown is described. A modified formulation of the harmonic-balance technique is used to suppress the degenerate (DC) solution. A novel procedure is introduced for the generation of a starting point for the state-variable harmonics, from which a mixed-mode Newton iteration can be safely started. The overall method leads to the desired steady-state solution in a direct way without requiring trials.

Detection of across-frequency differences in fundamental frequency

Abstract: Listeners discriminated between pairs of complex sounds, each consisting of two groups of components. Two harmonic complexes were played out through separate channels, and each filtered to obtain a ‘‘lower’’ and a ‘‘higher’’ group. The ‘‘carrier fundamental frequencies (F0s)’’ of both groups were usually 125 Hz; only those components in the lower group were resolvable by the peripheral auditory system. For the standard stimulus, the F0s of the two groups were frequency modulated coherently with each other, so that they were always equal. For the signal, the F0s of the two groups were modulated incoherently (π modulator delay), so that they differed by an amount that varied sinusoidally between values proportional to the depth of FM (the dependent variable). Stimuli were usually presented in continuous pink noise. The results showed that (i) when the components were added in sine or cosine phase, the mean threshold across listeners corresponded to a zero‐peak modulation depth of 6%–7% (rms mistuning=8.5%–10%); (ii) performance dropped to chance when the upper components were added in alternating sine–cosine phase, but was only moderately affected by the phase of the lower components; (iii) threshold for sine‐phase stimuli improved by a factor of 1.6 when noise in the frequency region of the two component groups was removed; (iv) threshold increased moderately with increases in the frequency separation between the two component groups; (v) threshold dropped markedly when the F0s of both groups of components were increased so as to be resolvable by the peripheral auditory system; and (vi) performance dropped to chance when the nominal carrier F0s of the two groups of components differed from each other. It is concluded that listeners can perform simultaneous comparisons of F0s derived from resolved and unresolved harmonics, and that their performance on this task is fairly robust. Implications for the perceptual segregation of concurrent complex sounds, and for models of pitch perception, are discussed.

Periodicity of maskers not targets determines ease of perceptual segregation using differences in fundamental frequency

Abstract: Meddis and Hewitt [J. Acoust. Soc. Am. 91, 233–245 (1992)] proposed a model of the use of differences in fundamental frequency to segregate competing sound sources. Key features of the model are: (i) a bank of bandpass filters, to simulate peripheral frequency analysis; (ii) autocorrelation, to determine the periodicities present in each channel; (iii) pooling of autocorrelation functions across channels, to determine the dominant periodicity. Evidence of the dominant source is found by grouping channels containing the dominant periodicity. Evidence of the nondominant source is found in the remaining channels. The model predicts that the periodicity of the dominant source, rather than the nondominant source, determines the ease of segregation. To test the prediction, thresholds for the identification of ‘‘target’’ vowels were measured in the presence of ‘‘masking’’ vowels. Targets and maskers were composed of sinusoids placed either harmonically or randomly in frequency. Masked thresholds were significantly lower when maskers were harmonic rather than random, but the harmonicity of the targets had little effect. Thus, the results are compatible with the predictions of Meddis and Hewitt’s model and are incompatible with models which attempt to compute the pitches of both sources prior to segregation.

Errors in attenuation measurements due to nonlinear propagation effects

Abstract: An investigation into the influence of finite amplitude distortion on narrow‐band ultrasonic attenuation measurements is described. Measurements have been made using a through‐transmission substitution technique in the nonlinear field of a 5‐MHz plane‐piston transducer driven under tone‐burst conditions. Various transducer excitation levels were used to generate a range of shock parameters σ at the position of the measuring hydrophone up to a maximum of 3. The influence of the resulting loss in amplitude at the fundamental frequency has been studied by measuring the transmission properties of reference attenuators consisting of Dow Corning‐710 fluid‐filled cells of various thickness. The presence of nonlinear distortion in the acoustic waveform produces overestimates of the measured transmission coefficients. The magnitude of the error has been shown to depend on the value of σ, the small signal transmission loss of the sample and its position in the acoustic field. In some situations, the error was as hi...