• The Journal of the Acoustical Society of Korea
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• v.31 no.3
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• pp.197-204
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• 2012

In this thesis, studied the method to minimize the changes in frequency response and level due to the variation of the distance from the source to the microphone. selecting three microphones (omni directional, cardioid, super cardioid) which are being used generally, frequency responses were measured in accordance with the distance changes. Gotten the difference from the reference as the result of measurement, changed responses for each frequency range were compensated in comparison of the original human vocal source. In low frequency range, the low frequency boost caused by the proximity effect and decrease in accordance with the distance were compensated. The variation in mid-frequency range is comparatively small, however since the mid-range is the most important part of the human vocal signal, were compensated the mid-frequency range in comparison of the reference. The human vocal signal variation in high frequency range is extremely small and the high frequency is compensated close to the original source without difficulty. Understanding the microphone characteristics and compensations, this study showed that the response can be maintain among the change of the distance from the source to the microphone.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.317-322
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• 2001

정보 통신 기술의 발달이 인간 생활에 많은 편리함을 가져다 주었지만 개인의 정보 유출이나 소음 공해 등의 여러 가지 문제점도 야기 시켰다. 특히 휴대 전화 통화시 사용자의 개인적인 정보들이 공공 장소에서 그대로 노출이 되고, 또 그러한 통화로 인해서 타인에게 소음 피해를 주기도 한다. 이러한 병폐를 막기 위해서 휴대 전화 사용자는 최대한 작은 소리로 통화를 하되, 상대방에게 의도하고자 하는 바를 확실히 전달하여야 한다. 그러기 위해서는 휴대 전화에 근접 통화가 가능해야 하며, 일정한 방향의 방향성을 가져서 주위의 잡음에 대해 독립적으로 작동하도록 해야한다. 본 논문에서는 이러한 기능을 향상시키기 위하여 음향학적 이론을 바탕으로 휴대전화에 사용되어지는 마이크로폰을 새로 설계, 제작하고 그 성능을 시험하였다. 아주 작은 소리로 근접 통화를 할 때 발생하는 팝핑(popping) 현상이 최소한이 되도록 미세관 배열을 적용하였으며, 외부 소음 영향을 줄이기 위하여 방향성을 증폭시키고자 음원의 위치에 초점을 맞추는 기술을 적용하였다. 방향성 증폭은 4개의 마이크로폰 사용과 근거리 음원의 방향성 증가를 위한 신호 처리기술을 적용하였다. 이 기술의 적용 효과를 실험을 통하여 검증할 수 있었다.

• The Journal of the Acoustical Society of Korea
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• v.24 no.7
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• pp.423-430
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• 2005

In this paper. a microphone array beamforming algorithm that reduces the signal distortion caused by reverberation and near-field effect in car environment is proposed. When reverberation or near-field effect is present, an optimum beamformer should be constructed with a steering vector consisting of transfer functions between source and microphones, but it is generally difficult to estimate transfer functions on-line without knowledge of the source signal. Instead, a sub-optimal beamforming algorithm that reduces signal distortion is proposed. It is constructed with steering vectors consisting of relative transfer functions between reference sensor and other sensors. In order to evaluate the performance of the proposed algorithm. we had recorded noisy speech database in a car, and performed speech recognition experiments with HMM Toolkit (HTK) released by Cambridge University. The recognition rate of the proposed algorithm was 15 percents higher than that of the conventional far-field beamformers in best case.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.12
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• pp.310-319
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• 2020

Korea estimates the traffic noise by measuring the total traffic noise when the traffic passes (SPB; Statistical Pass-By). Another method (CPX; Close Proximity) directly measures the tire/road noise by installing a microphone near the tire. The CPX method is not a formal test method in Korea. There has been little research between CPX and SPB. This study proposes a method for estimating SPB, using the CPX, which is easy to measure. This study used the results of a large-scale test conducted by Korea Expressway Corporation (KEC) and a research paper on CPX in this section. The results by the KEC showed that the low noise pavement has a noise reduction of 10.4dB. In CPX research, the noise reduction was 10.7dB and was similar to 10.4dB in SPB. This study shows why the noise reduction is the same regardless of the position, the reason that the amount of noise reduction is similar, the difference of the noise according to the position of the microphone using the concept of noise summation and distance reduction. This study shows that including the CPX as a variable in the traffic noise prediction program is very important to improve noise prediction reliability.