• MALSORI
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• no.60
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• pp.181-190
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• 2006

This paper describes a speech enhancement scheme that leads to significant improvements in recognition performance when used in the ASR front-end. The proposed approach is based on adaptive comb filtering and an MMSE-related parameter estimator. While adaptive comb filtering reduces noise components remarkably, it is rarely effective in reducing non-stationary noises. Furthermore, due to the uniformly distributed frequency response of the comb-filter, it can cause serious distortion to clean speech signals. This paper proposes an improved comb-filter that adjusts its spectral magnitude to the original speech, based on the speech absence probability and the gain modification function. In addition, we introduce the modified comb filtering-based speech enhancement scheme for ASR in mobile environments. Evaluation experiments carried out using the Aurora 2 database demonstrate that the proposed method outperforms conventional adaptive comb filtering techniques in both clean and noisy environments.

• Journal of IKEEE
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• v.20 no.4
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• pp.385-391
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• 2016

We demonstrated experimentally a variable optical frequency comb source using a cascaded dual parallel Mach Zehnder modulator (DPMZM) and a phase modulator (PM). With this simple configuration and applying low drive voltages, we generated variable comb source composed of spectral lines 3, 5, 7, 9 and 11 with 10-GHz frequency spacing, also generated 2 and 3 spectral lines with 20 GHz frequency spacing. The generated comb source maintains high spectral coherence across the entire bandwidth with good spectral flatness (within 1-dB for 2, 3, 5, 7 comb lines, within 2-dB for 9-comb lines and within 3-dB for 11 comb lines). The flat and variable comb source is mainly achieved by manipulating 6 operating parameters of DPMZM, setting RF amplifier gain, connected at phase modulator and phase shifters. Hence the method is simple and offers great flexibility in achieving flat and variable comb spectrum, which is experimentally demonstrated. This brings advantages of power efficiency due to low driving voltages, simplicity and cost effectiveness to the system.

• Current Optics and Photonics
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• v.5 no.3
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• pp.289-297
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• 2021

We describe a comb-mode resolving spectroscopic technique by direct time-domain phase correction of unstable interferograms obtained from loosely locked two femtosecond lasers. A low-cost continuous wave laser and conventional repetition rate stabilization method were exploited for locking carrier and envelope phase of interferograms, respectively. We intentionally set the servo control at low bandwidth, resulting in severe interferograms' fluctuation to demonstrate the capability of the proposed correction method. The envelope phase of each interferogram was estimated by a quadratic fit of carrier peaks to correct timing fluctuation of interferograms in the time domain. After envelope phase correction on individual interferograms, we successfully demonstrated 1 Hz linewidth of RF comb-mode over 200 GHz optical spectral-bandwidth with 10-times signal-to-noise ratio (SNR) enhancement compared to the spectrum without correction. Besides, the group delay difference between two femtosecond pulses is successfully estimated through a linear slope of phase information.

• MALSORI
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• no.46
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• pp.65-76
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• 2003

In this paper, we employ the adaptive comb filtering for effective noise reduction in mobile communication environment. Adaptive comb filtering is a well-known method for noise reduction, but requires correct pitch period and must be applied just in voiced speech frames. To satisfy these requirements we use two kinds of information extracted from speech packets, one of which is the pitch period information measured precisely by a speech coder and the other is the frame rate information related to a decision on speech or silence frame. Experiments on speech recognition system confirm the efficiency of this method. Feature parameters employing this method give superior performance in noise environment to those extracted directly from output speech.

• Proceedings of the KSPS conference
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• 2003.05a
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• pp.203-206
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• 2003

In this paper, we employ the adaptive comb filtering for effective noise reduction in mobile communication environment. Adaptive comb filtering is a well- known method for noise reduction, but requires the correct pitch period and must be applied just in voiced speech frames. To satisfy these requirements we use two kinds of information extracted from speech packets, one of which is the pitch period information measured precisely by a speech coder and the other is the frame rate information related to a decision on speech or silence frame. Experiments on speech recognition system confirm the efficiency of this method. Feature parameters employing this method give superior performance in noise environment to those extracted directly from output speech.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.5 s.170
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• pp.72-79
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• 2005

Gearing system emits inconsistent noise from gear teeth impact in case of gear defects. But, it is not easy for inspection operator in production line to distinguish objectively the defective product. Therefore, customer complains continuously bad noise of the geared motor. Because impulsive signal at low frequency has a tendency not to appear in frequency domain, it is difficult to separate the gear inconsistent noise of defective gear from overall geared motor's noise using general signal processing method such as FFT. In this paper, the method to estimate more objectively the inconsistent noise of gearing system and to measure the quantities is suggested. Suggested method uses Cepstrum, Autocorrelation, Comb Lifter and Inverse Cepstrum by turns to make objective quantities about noise level.

• Journal of Life Science
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• v.19 no.1
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• pp.52-57
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• 2009

This study was carried out to investigate the antioxidative and antimicrobial activities of Celastrus orbiculatus (CO). CO was extracted with methanol and then further fractionated with n-hexane (COMH), butanol (COMB), methanol (COMM) or aqueous (COMA) to get active fractions. The antioxidative activity of fractions from CO was investigated by measuring the scavenging activities of CO against DPPH radical, peroxynitrite ($ONOO^-$) and reactive oxygen speicies (ROS). Among the various solvent fractions, the COMB showed a marked scavenging effect against DPPH radical, peroxynitrite ($ONOO^-$) and reactive oxygen species(ROS). The antimicrobial activity was increased in proportion to its concentration by the paper disk method. Among the various solvent fractions, the COMM and COMB fractions of CO showed strong antimicrobial activities. The results suggest that The CO may be suitable for development as a food preservative and alternative antioxidant.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.6
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• pp.124-131
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• 2008

There are many factors which affect the acoustical properties of a micro-speaker. Among the factors, the shape of the diaphragm is considered in this study. As an investigating method, the finite element methods and measurement techniques applied to study the acoustical properties according to diaphragm shape. In order to vary the stiffness of the diaphragm, the some patterns of comb teeth, such as the angle and the number of comb teeth, are applied to diaphragm. We can confirm that the change of the stiffness by the changing diaphragm shape affects the vibration and sound properties of the speaker. As a result, the reduction of the angle of the comb teeth increases the diaphragm stiffness and shifts the resonance frequency to a higher frequency range. The number of the comb teeth is related to the stiffness of the edge part.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.4
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• pp.399-407
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• 2010

SC-FDMA system uses DFT-spreading method for reducing the PAPR of OFDM signal, which improves the power efficiency. Block type pilot is used in SC-FDMA system. However, there are ICI due to the inevitable phase noise and frequency offset that can be generated from the Doppler frequency and inaccuracy between the transceiver oscillators. This ICI definitely degrades the BER performance. To overcome this problem and estimate the channel efficiently, we like to propose ICI compensation algorithm for the SC-FDMA system with comb type pilot. SLM method is additionally included for the PAPR reduction when pilot is assigned in comb type. Finally, it is confirmed that the ICI due to the phase noise and frequency offset is efficiently compensated by the suggested algorithm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.9
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• pp.965-970
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• 2010

Because of a large number of subcarriers, the high PAPR(Peak-to-Average Power Ratio) is the major drawback of NC-OFDM system used for wireless communication system. Comb type pilot assignment is more efficient and lower computational complexity for the channel estimation than the block type pilot. However, even if the CAZAC(Constant Amplitude Zero Autocorrelation) matrix transform is used for the PAPR reduction of the data symbols, PAPR increases when the pilot is inserted in comb type with the data symbols. Therefore, in this paper, we additionally use a new SLM technique in order to lower the PAPR again even in the comb type pilot. Also, a new SLM technique suggested in this paper does not need any additional bandwidth for sending selection information for SLM. This combined method has good PAPR reduction performance and efficient data transmission.