• The Journal of the Acoustical Society of Korea
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• v.16 no.2
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• pp.71-79
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• 1997

In this paper, a codeword-dependent distance normalization(CDDN) and an instar-formed fuzzy smoothing of output distribution are proposed for robust estimation of output probabilities in the FVQ(fuzzy vector quantization)-DHMM(discrete hidden Markov model). The FVQ-DHMM is a variant of DHMM in which the state output probability is estimated by the sum oft he product of the output probability and its weighting factor for each codeword on an input vector. As the performance of the FVQ-DHMM is influenced by weighting factor and output distribution from a state, it is required to get a method to get robust estimation of weighting factors and output distribution for each state. From experimental results, the proposed CDDN method has reduced 24% of error rate over the conventional FVQ-DHMM, and also reduced 79% of error rate when the smoothing of output distribution is also applied to the computation of an output probability. These results indicate that the use of CDDN and the fuzzy smoothing of output distribution to the FVQ-DHMM lead to improved recognition, and therefore it may be used as an alternative to the robust estimation of output probabilities for HMMs.

• The Journal of the Acoustical Society of Korea
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• v.10 no.6
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• pp.71-76
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• 1991

적응 어레이 시스템에서 최적해에 도달하기 위한 계수들의 수렴 속도는 공분산 행렬의 고유치 분포율에 의해 지배된다. 본 논문에서는 우선 GSC의 고유치 분포율을 구하였다. 또한 conherent 상황에 서 GSC의 출력 파워 식을 유도하였다.

• The Journal of the Acoustical Society of Korea
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• v.15 no.2
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• pp.49-54
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• 1996

In this paper, a photorefractive crystal is utilized as an output device, specifically as a time integrating detector for an acousto-optic correlator. In a standard time integrating acousto-optic architecture which uses CCDs, the output correlation signal is presented which includes bias. This results in a limitation on the effective dynamic range of the correlator. In a photorefractive crystal, light without spatial variation does not produce a cumulative bias signal and hence when the photorefractive crystal is used as the integrating detector, the correlation signal can be recorded and read out without bias. Important characteristics such as linearity dynamic range and integration time are also presented in this paper.

• 전자공학회논문지 IE
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• v.48 no.3
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• pp.10-15
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• 2011

In the case of designing an acoustic transducer for high power application, we usually aim to transfer the source electric energy to the output acoustic energy as large as possible. For this purpose, we should match the impedance of the power amplifier to the impedance combined with the acoustic transducer impedance and the radiation impedance. Especially if we have electrical source with almost zero impedance, we need improve the power factor of the acoustic transducer in the load. In this paper, we propose a broad band impedance matching method by the improvement of power factor, which applies ABCD matrix.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.175-178
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• 2004

각각 2개의 마이크로폰을 내장한 귓속형 보청기를 양쪽귀에 착용한 상태에서 소리의 지향성을 시뮬레이션하고 전기음향실험으로 비교하였다. 지향성 보청기의 신호 대 잡음 비율 향상을 고려하였다. 시뮬레이션을 위해 경계요소기법을 사용하였으며 본 논문에 의해 밝혀진 주파수 대역에서의 시간 지연을 DSP칩을 내장한 디지털 보청기의 지향성 조절 파라미터로 사용하고자 한다. 마이크로폰 사이의 간격을 10mm로 하였다. 가장 최적한 지향성이 출력 되기 위한 위상을 계산하였다.

• The Journal of the Acoustical Society of Korea
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• v.11 no.4
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• pp.31-35
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• 1992

Cavity resonances are caused by combustion such as the rapid of pressure rise that occurs from knock in high power gasoline engines. These resonances generally occur at frequencies greater than 5KHz. Analysis of these resonances is important for knock control system design in high power gasoline engines. In this paper, in order to design knock control system for the high power gasoline engine, knock phenomena that occur in chamber were analized theoretically and resonance frequencies of knock signals were predicted. Also, experiments were performed using Soupe x-engine and non-resonance type knock sensor of Bosch co. in Germany. In the result, good agreement was obtained between theoretical prediction and experimental observation.

• The Journal of the Acoustical Society of Korea
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• v.29 no.2
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• pp.97-101
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• 2010

FIR type system identification with noisy input and output data can be solved by a total least squares (TLS) estimation. However, the performance of the TLS estimation is very sensitive to the ratio between the variances of the input and output noises. In this paper, we propose an iterative convex combination algorithm between TLS and least squares (LS). This combined algorithm shows robustness against the noise variance ratio. Consequently, the practical workability of the TLS method with noisy data has been significantly broadened.

• The Journal of the Korea Contents Association
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• v.6 no.10
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• pp.9-16
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• 2006

In this paper, the acoustic model output of CSR(Continuous Speech Recognition) was used to analyze news data News database used in this experiment was consisted of 2,093 articles. Due to the low efficiency of language model, conventional Korean CSR is not appropriate to the analysis of news data. This problem could be handled successfully by introducing post-processing work of recognition result of acoustic model. The acoustic model more robust than language model in Korean environment. The result of post-processing work was made into KIF(Keyword information file). When threshold of acoustic model's output level was 100, 86.9% of whole target morpheme was included in post-processing result. At the same condition, applying length information based normalization, 81.25% of whole target morpheme was recognized. The purpose of normalization was to compensate long-length morpheme. According to experiment result, 75.13% of whole target morpheme was recognized KIF(314MB) had been produced from original news data(5,040MB). The decrease rate of absolute information met was approximately 93.8%.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.5
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• pp.91-97
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• 2012

Recently, the performances of electrical and electronic devices are improving while the sizes are becoming smaller. As sound-generating systems, the two-dimensional speakers have been developed in place of conventional three-dimensional ones. Piezoelectric materials show the mechanical vibrations due to the voltage applied from outside the materials. The early film speakers had a limitations of output power in that it was not easy to make the conducting macromolecular films on the surfaces of the materials due to the internal chemical properties of materials. We have adopted the corona surface treatment in order to improve the output characteristics by increasing the adhesion of the coating material on to the surface of the center material of piezo film. The results showed the improvement of output power in the wider range of operating frequencies.

• The Journal of the Acoustical Society of Korea
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• v.29 no.6
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• pp.355-364
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• 2010

Considering biological safety, it is very important to measure acoustic power from ultrasonic array probe for diagnostic ultrasound imaging applications. In this paper, to measure acoustic power from each element on array probe for ultrasonic diagnostic equipment, we reconstruct and automate the acoustic power measurement system. The acoustic power from linear, phased and curved array were measured and analyzed. As a result of measurement, the effects caused by directivity of sound beam from curved array were founded. To remove these effects, we developed and applied the correction model. The proposed system is useful to evaluate characteristics of the acoustical output power of array probe.