• The Journal of the Acoustical Society of Korea
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• v.40 no.3
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• pp.234-240
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• 2021

In this paper, the mask-based speech enhancement is improved for effective speech recognition in noise environments. In the mask-based speech enhancement, enhanced spectrum is obtained by multiplying the noisy speech spectrum by the mask. The VoiceFilter (VF) model is used as the mask estimation, and the Spectrogram Inpainting (SI) technique is used to remove residual noise of enhanced spectrum. In this paper, we propose a combined loss to further improve speech enhancement. In order to effectively remove the residual noise in the speech, the positive part of the Triplet loss is used with the component loss. For the experiment TIMIT database is re-constructed using NOISEX92 noise and background music samples with various Signal to Noise Ratio (SNR) conditions. Source to Distortion Ratio (SDR), Perceptual Evaluation of Speech Quality (PESQ), and Short-Time Objective Intelligibility (STOI) are used as the metrics of performance evaluation. When the VF was trained with the mean squared error and the SI model was trained with the combined loss, SDR, PESQ, and STOI were improved by 0.5, 0.06, and 0.002 respectively compared to the system trained only with the mean squared error.

• The Journal of the Acoustical Society of Korea
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• v.14 no.6
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• pp.27-31
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• 1995

In this paper, the determination method of available bandwidth for automation of the split-spectrum processing(SSP) has been studied. The SSP is used for the visibility enhancement of the ultrasonic signal with grain noise. Even though the SSP has proved useful in signal-to-noise ratio enhancement, its application and automation have been limited due to ambiguity in the determination of available bandwidth. Until recently, it is the usual practice to optimize the available bandwidth by trial and error. The spectral histogram is the statistical distribution of the spectral windows that is selected by the minimization algorithm with the whole band of the spectrum of the received ultrasonic signal. Since the available bandwidth can be determined adaptively using spectral histogram, this method can be used for automation of the SSP. In order to evaluate the determination technique of the available bandwidth using spectral histogram, this method is applied to experimental ultrasonic data. The experimental results show that the spectral histogram is an efficient method for determination of the available bandwidth and automation of the SSP.

• Macromolecular Research
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• v.10 no.2
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• pp.60-66
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• 2002

The morphology, dynamic mechanical behavior and fracture behavior of polyetherimide (PEI)/dicyanate semi-interpenetrating polymer networks (semi-IPNs) with a morphology spectrum were analyzed. To obtain the morphology spectrum, we disported PEI particles in the procured dicyanate resin containing 300 ppm of zinc stearate catalyst. The semi-IPNs exhibited a morphology spectrum, which consisted of nodular spinodal structure, dual-phase morphology, and sea-island type morphology, in the radial direction of each dispersed PEI particle due to the concentration gradient developed by restricted dissolution and diffusion of the PEI particles during the curing process of the dicyanate resin. Analysis of the dynamic mechanical data obtained by the semi-IPNs demonstrated that the transition of the PEI-rich phase was shifted toward higher temperature as well as becoming broader because of the gradient structure. The semi-IPNs with the morphology spectrum showed improved fracture energy of 0.3 kJ/$m^2$, which was 1.4 times that of the IPNS having sea-island type morphology. It was found that the partially introduced nodular structure played a crucial role in the enhancement of the fracture resistance of the semi-IPNs.

• The Journal of the Acoustical Society of Korea
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• v.29 no.2E
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• pp.86-99
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• 2010

This paper analyzes the performance of various single channel speech enhancement algorithms when they are applied to automatic speech recognition (ASR) systems as a preprocessor. The functional modules of speech enhancement systems are first divided into four major modules such as a gain estimator, a noise power spectrum estimator, a priori signal to noise ratio (SNR) estimator, and a speech absence probability (SAP) estimator. We investigate the relationship between speech recognition accuracy and the roles of each module. Simulation results show that the Wiener filter outperforms other gain functions such as minimum mean square error-short time spectral amplitude (MMSE-STSA) and minimum mean square error-log spectral amplitude (MMSE-LSA) estimators when a perfect noise estimator is applied. When the performance of the noise estimator degrades, however, MMSE methods including the decision directed module to estimate a priori SNR and the SAP estimation module helps to improve the performance of the enhancement algorithm for speech recognition systems.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.78.4-79
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• 2017

Thermal inflation is an additional inflationary mechanism before the big bang nucleosynthesis, which solves the moduli problem and naturally provides a plausible dark matter candidate. Thermal inflation leaves a slight enhancement followed by huge suppression of a factor of ~50 in the curvature and matter power spectrum, which can be expressed in terms of a single characteristic scale $k_b$. Here we describe the observability of the small-scale features of thermal inflation from various observations, such as CMB distortion, satellite galaxy abundance in the Milky-Way-sized galaxies, and 21-cm power spectrum before the epoch of reionization.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.363.2-363
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• 2002

The spectrum of impulse response signal from an impulse hammer testing is widely used to obtain frequency response function(FRF) of the structure. However the FRFs obtained from impact hammer testing have not only leakage errors but also finite record length errors when the record length for the signal processing is not sufficiently long. The errors cannot be removed with the conventional signal analyzer which treats the signals as if they are always steady and periodic. (omitted)

• Proceedings of the Korea Information Processing Society Conference
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• 2016.04a
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• pp.83-85
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• 2016

C-RAN (Cloud Radio Access Network) structure is the most popular approach for 5G stander, it employs CoMP (Coordinated Multiple Points Transmission/Reception) to enhance frequency utilization and increase throughput for cell-edge users. C-RAN mainly includes two parts: baseband units (BBU) and remote radio heads (RRH). In this paper we propose a new resource block allocation (spectrum allocation) scheme by the permutation and combination of BBUs, and we also use the CoMP (Coordinated Multiple Points Transmission/Reception) technique according to the different environment to improve the spectrum utilization and reduce resource waste in different environment. The simulation results expound that the scheme significantly enhances throughput and improves the spectrum utilization.

• Bulletin of the Korean Chemical Society
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• v.34 no.1
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• pp.68-74
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• 2013

The surface enhanced Raman spectrum of juglone, a traditional natural dye, has been observed by a custom-built micro-Raman setup. The spectral features of juglone significantly differ from those of lawsone, a structural isomer of juglone; only small red shifts of the double bond stretching bands are observed, and strong SERS bands are observed in the lower frequency regions as well. The DFT computations reveal that juglone coordinated to an $Ag^+$ adatom with $H^+$ release best correlates with the observed vibrational characteristics in the SERS spectrum among the plausible configurations of juglone coordinated to an adatom on the Ag surface, in line with the previously studied lawsone case. The differences in the SERS spectra of juglone and lawsone are attributed to the different locations of the hydroxyl group in the two isomers.

• Proceedings of the KIEE Conference
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• 1993.07a
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• pp.277-280
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• 1993

When the noise is mainly caused by a detector and is statistically independent of the incident radiation, the multiplexing inherent in the Hadamard transform (HT) spectrometer can provide an improved spectrum-estimate. A spectrum-estimate can be further improved when any nonidealities in the system are compensated. In this research, three spectrum-estimation methods for an HT spectrometer having a nonideal mask are discussed in terms of computational efficiency, statistical bias, the sources of error, and the mean-square error associated with a given estimate. In addition, the results obtained from computer simulations are used to verify the theoretical foundation of each method.

• Journal of Satellite, Information and Communications
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• v.12 no.2
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• pp.65-70
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• 2017

The structure of MMSE receiver front-ended by CMA(Constant Modulus Array) array working in CDMA forward link which is applicable to LEO spread spectrum satellite communication system is proposed. By using the despreaded pilot signal of forward link as a reference signal, the CMA array can capture multi-path signals securely even in severely faded LEO satellite channel. The remaining MAI (Multiple Access Interference) is cancelled by the cascaded MMSE receiver. Besides theoretical development, through relevant computer simulation, it is proved that the proposed system shows much better BER performance than any other possible candidate systems. As a spatio-temporal receiver mounted on a mobile vehicle, the proposed system also reduces implemental cost and complexity by adopting the simplest algorithm for its spatial and temporal domain processing.