• Journal of the Korean earth science society
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• v.34 no.5
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• pp.393-401
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• 2013

Spherical harmonics power spectrum of the geopotential field of Gaussian-bell type on the sphere was investigated using integral formula that is associated with Legendre polynomials. The geopotential field of Gaussian-bell type is defined as a function of sine of angular distance from the bell's center in order to guarantee the continuity on the global domain. Since the integral-formula associated with the Legendre polynomials was represented with infinite series of polynomial, an estimation method was developed to make the procedure computationally efficient while preserving the accuracy. The spherical harmonics power spectrum was shown to vary significantly depending on the scale parameter of the Gaussian bell. Due to the accurate procedure of the new method, the power (degree variance) spanning over orders that were far higher than machine roundoff was well explored. When the scale parameter (or width) of the Gaussian bell is large, the spectrum drops sharply with the total wavenumber. On the other hand, in case of small scale parameter the spectrum tends to be flat, showing very slow decaying with the total wavenumber. The accuracy of the new method was compared with theoretical values for various scale parameters. The new method was found advantageous over discrete numerical methods, such as Gaussian quadrature and Fourier method, in that it can produce the power spectrum with accuracy and computational efficiency for all range of total wavenumber. The results of present study help to determine the allowable maximum scale parameter of the geopotential field when a Gaussian-bell type is adopted as a localized function.

• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.409-412
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• 2002

The delta modulation used for controlling the speed of an induction motor has high peak of harmonic spectrum at low speed range causing acoustic noises in the induction motor. This paper proposes to suppress the harmonics by synchronizing the reference signal with the hysteresis windows for controlling the distribution of the switching frequency. As a result we can decrease the peak of harmonic spectrum. The simulation results show that the peak spectrum of harmonics can be reduced up to 60%.

• Speech Sciences
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• v.10 no.2
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• pp.85-95
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• 2003

In speech signal processing, it is very important to detect the pitch exactly in speech recognition, synthesis and analysis. If we exactly pitch detect in speech signal, in the analysis, we can use the pitch to obtain properly the vocal tract parameter. It can be used to easily change or to maintain the naturalness and intelligibility of quality in speech synthesis and to eliminate the personality for speaker-independence in speech recognition. In this paper, we proposed a new pitch detection algorithm. First, positive center clipping is process by using the incline of speech in order to emphasize pitch period with a glottal component of removed vocal tract characteristic in time domain. And rough formant envelope is computed through peak-fitting spectrum of original speech signal infrequence domain. Using the roughed formant envelope, obtain the smoothed formant envelope through calculate the linear interpolation. As well get the flattened harmonics waveform with the algebra difference between spectrum of original speech signal and smoothed formant envelope. Inverse fast fourier transform (IFFT) compute this flattened harmonics. After all, we obtain Residual signal which is removed vocal tract element. The performance was compared with LPC and Cepstrum, ACF. Owing to this algorithm, we have obtained the pitch information improved the accuracy of pitch detection and gross error rate is reduced in voice speech region and in transition region of changing the phoneme.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.4
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• pp.85-92
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• 2000

The pulsating pressure waves are composed of fundamental frequency and higher order harmonics in exhaust pipe of engines. The nonlinearity in exhaust pipe is caused by their interactions. The error which is between prediction and measurement is induced by the nonlinearity. We can not explain this phenomenon using linear acoustic theory which is existing theory. So power spectrum which was used in linear theory is not useful. Bispectrum and bicoherence functions which are a higher order spectrum are applicable to explain this phenomenon. This paper proposes a nonlinear effect of pulsating pressure waves. The phenomenon proposed here is identified by using of higher order spectrum density functions.

• The Journal of the Acoustical Society of Korea
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• v.22 no.2E
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• pp.62-68
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• 2003

This paper addresses a novel noise-compensation scheme to solve the mismatch problem between training and testing condition for the automatic speech recognition (ASR) system, specifically in car environment. The conventional spectral subtraction schemes rely on the signal-to-noise ratio (SNR) such that attenuation is imposed on that part of the spectrum that appears to have low SNR, and accentuation is made on that part of high SNR. However, these schemes are based on the postulation that the power spectrum of noise is in general at the lower level in magnitude than that of speech. Therefore, while such postulation is adequate for high SNR environment, it is grossly inadequate for low SNR scenarios such as that of car environment. This paper proposes an efficient spectral subtraction scheme focused specifically to low SNR noisy environment by extracting harmonics distinctively in speech spectrum. Representative experiments confirm the superior performance of the proposed method over conventional methods. The experiments are conducted using car noise-corrupted utterances of Aurora2 corpus.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.9
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• pp.1013-1021
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• 2004

This paper presents the results of spectrum analysis of leakage current waveforms on contaminated polymer insulators under fog conditions. This is a basic study on development of a monitoring for aging degree and surface pollution state using distortion rate(%) of 3rd and 5th harmonics according fundamental frequency[60Hz] under environment conditions. Arcing on the surface was always associated with distortion in the leakage current ; hence the low frequency components of the leakage current can be used as a means to evaluate the surface degradation. The results indicate that the distortion rate by spectrum analysis is available for the monitoring of contamination condition of EPDM Polymer insulators.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.1
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• pp.149-158
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• 2015

This paper proposes a subband filtering technique to the MUSIC and the ESPRIT algorithm for estimating the magnitude and frequency of the harmonics of power signal. In proposed method, the input power signal is decomposed to the odd harmonics and the even harmonics respectively by the filter bank system. The amplitude and the frequency estimation of the decomposed harmonics are carried out using the MUSIC and the ESPRIT method. Subband filtering can reduce the autocorrelation matrix size of input data, and spectrum leakage between adjacent harmonics. Therefore, this subband technique has advantage in computational cost and estimation accuracy compared to fullband MUSIC and ESPRIT. To demonstrate the performance of the method, computer simulations are performed to the synthesized input signal, and experiment results are compared in subband and fullband cases.

• Journal of Korea Multimedia Society
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• v.9 no.7
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• pp.801-807
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• 2006

This study analyzed the timbral characteristics of Pliri by basis step for the sound synthesis for Piri, Korean traditional musical Instrument. By analyzing this material, we can find out three characteristics about the study of the spectrum analysis for the sound synthesis of Piri. First, compared the timbral characteristics of Piri with Oboe through the spectrum analysis, Second, analyzed the timbral characteristics by the sound occurrence process through the time zone analysis of the attack part of the sound started. Finally, analyzed the special characteristics of the vibrato that is important role of musical instrument performance. As a result, the timbral characteristics of Piri is that the volume of the high harmonics was appeared to be high unlike the general classical instrument and the noise quantity rapidly decreased in the sound attack part but the volume value of harmonics increased. And also vibrato that is performance technique is changed pitch and amplitude at the same time by contrast with the general classical instrument. Thus, the timbral characteristic of Piri by the harmonics and the timbre change by the attack part which is sound occurrence process and the change of the pitch and amplitude in the vibrato is characteristic that represented unique quality of Piri. We expect that this achievement can be applied to sound synthesis.

• Speech Sciences
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• v.11 no.1
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• pp.7-20
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• 2004

In this paper, we propose a two-step noise compensation algorithm in feature extraction for achieving robust speech recognition. The proposed method frees us from requiring a priori information on noisy environments and is simple to implement. First, in frequency domain, the Harmonics-based Spectral Subtraction (HSS) is applied so that it reduces the additive background noise and makes the shape of harmonics in speech spectrum more pronounced. We then apply a judiciously weighted variance Feature Vector Normalization (FVN) to compensate for both the channel distortion and additive noise. The weighted variance FVN compensates for the variance mismatch in both the speech and the non-speech regions respectively. Representative performance evaluation using Aurora 2 database shows that the proposed method yields 27.18% relative improvement in accuracy under a multi-noise training task and 57.94% relative improvement under a clean training task.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.53 no.12
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• pp.739-750
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• 2004

In case while M(modulation index) is more than 0.7, the spectrum of motor voltage and current of a conventional two-phase SRP-PWM scheme are not reduced considerably. To solve the problems of a conventional two-phase SRP-PWM, this paper proposes a two-phase SRP-PWM(DZSRP-PWM) with double zero vector mode which zero vector is selected as V(111) in case of M >0.7, and zero vector is selected as V(000) if M < 0.7. For the validity of the proposed method, the PSIM simulations and experiments were achieved. And the simulation and experiment results show that the voltage and current harmonics all over the modulation index are spread to a wide band area.