• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.805-808
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• 2001

음성인식, 합성 및 분석과 같은 음성신호처리 분야에 있어서 기본주파수 즉, 피치를 정확히 검출하는 것은 중요하나 만일 음성신호의 기존주파수를 정확히 검출할 수 있다면 음성인식에 있어서 화자에 따른 영향을 줄일 수 있기 때문에 인식의 정확도를 높일 수 있고, 음성합성 시에 자연성과 개성을 쉽게 변경하거나 유지할 수 있다. 또한 분석시 피치에 동기 시켜 분석하면 성문의 영향이 제거된 정확한 성도 파라미터를 얻을 수 있다. 따라서 제안한 논문에서는 시간영역처리에서 시간영역파형에서 먼저 성도성분이 제거된 성문특성 즉 피치주기 성분을 강조하기 위해 음성신호의 기울기를 이용한 Positive 센터 클리핑를 수행하고 주파수 영역에서는 원신호의 스펙트럼과 센터클립된 신호의 스펙트럼과의 Peak-Fiting을 수행하고 선형 인터폴래이션(스무딩)을 통해 평탄화된 스펙트럼을 얻었다. 결과적으로 유성음 구간과 음성이 변하는 전이구간에서 G-peak가 강조된 더욱 정확한 Pitch를 검출할 수 있었다.

• The Journal of the Acoustical Society of Korea
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• v.11 no.1E
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• pp.42-49
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• 1992

시간 영역에서 음성의 피치 정보를 추출하는 새로운 알고리즘을 제안한다. 이 알고리즘은, 위상 이 일치하는 고조파 성분의 합은 위상이 일치하지 않는 고조파 성분의 합의 경우보다 주기 정보를 분명 히 나타낸다는 사실을 이용한 것이다. 즉, 음성 신호의 위상 성분을 0으로 되도록 하여 실질적으로 기본 파와 모든 고조파 성분의 위상을 일치시킨다. 이 알고리즘은 잡음이 없는 음성의 경우 0.18%의 조오류 를 보이며, 0dB 눅의 경우에도 3.63%의 조오류를 보임으로써 잡음에 강건한 성질이 있음을 알 수 있다. 또한 시간 영역에서의 결정 논리를 사용하므로 피치 해상도가 우수하다. 전반적인 실험결과는 제안된 알고리즘이 피치 검출에 상당히 효율적임을 나타낸다.

• The Journal of the Acoustical Society of Korea
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• v.24 no.7
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• pp.402-409
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• 2005

In this paper. we propose a coding method using a matching pursuit algorithm in a strongly periodic highband signal. Also. we propose an efficient quantizer for the estimated parameters : spectral magnitude and phase. Based on the error concealment principle and sinusoidal model. the MP algorithm requires the high-precision pitch period estimation. To estimate more accurate pitch period. the refined pitch obtained from lowband speech is used. which increases the efficiency of bit allocation. The spectral magnitude parameters are quantized by the method which is combined with MDCT (Modified Discrete Cosine Transform) and multi-stage structure. The spectral phase quantizer uses the $2{\pi}$ modular characteristic of phases and the weighted function by spectral magnitudes. To evaluate the efficiency of the proposed method. we applied it to analysis-by-synthesis system. Furthermore we suggest the possibillity of scalable wideband speech codecs based on band-split structure.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.10
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• pp.969-978
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• 2008

In a linear cascade experimental apparatus, when it adopts only few blades as well as satisfies the periodic condition between blades, it gives several advantages in experiment. In this study, wall design on a cascade experimental apparatus is conducted to obtain the periodic condition on two blades installed within a passage of which the width is double pitch. The Mach number difference on the blade surface obtained with the periodic and wall condition is chosen as an objective function, and twelve design variables which are related to the wall shape are selected. A wall shape is designed using a gradient-based optimization method. Adjustment of range and weighting function are applied to calculate the objective function to avoid unrealistic evaluation of the objective function. By applying these methods, the computed results show same flow structures obtained with the periodic condition.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.6
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• pp.527-536
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• 2009

A cascade apparatus was designed with only one blade. Its passage is a 160% width of the cascade pitch. This kind of apparatus can give more accurate experimental result than those applying multi-blades even though the apparatus is small. However, this causes difficulties to make the periodic condition along the pitchwise direction. In this study, sidewalls were designed to satisfy the periodic condition based on the flow structure using a gradient based optimization and a genetic algorism. The objective function was adopted the surface Mach number obtained on the cascade and fourteen design variables were selected for controlling sidewall shapes. The designed sidewalls using the genetic algorism shows better result.

• The Journal of the Acoustical Society of Korea
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• v.21 no.8
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• pp.727-734
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• 2002

A simple algorithm for discriminating voiced sounds in a speech is proposed in this paper. In addition to low-frequency energy and zero-crossing rate (ZCR), both of which have been widely used in the past for identifying voiced sounds, the proposed algorithm incorporates pitch variation to improve the discrimination rate. Based on TIMIT corpus, evaluation result shows an improvement of 13% in the discrimination of voiced phonemes over that of the traditional algorithm using only energy and ZCR.

• The Journal of the Acoustical Society of Korea
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• v.11 no.1
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• pp.35-41
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• 1992

A speaker identification scheme using the speaker-based VQ codecook of a sustained vowel is proposed and tested. With the pitch synchronous LPC vector of the sustained vowel /i/ as a feature vector, a VQ codebook size of 4 was found to be suitable to characterize each speaker's feature space. For 40 normal speakers (20 males, 20 females), we achieved the correct identification rate of 99.4% with a training data set, and 89.4% with a test data set with speech samples of only 50 pitch periods.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.73-76
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• 2002

본 논문에서는 8kbps의 전송율을 가진 ITU G.729 보코더와 PSOLA(Pitch Synchronized Overlap -Add) 알고리즘을 적용하여 전송율을 6kbps와 4kbp까지 낮출 수 있는 가변 전송율 보코더를 구현하였다. 제안한 방법은 4kbps일 경우에 G.729의 부호화전에 PSOLA를 적용하여 피치의 주기를 반으로 줄여 부호화한다. 이렇게 부호화된 데이터는 G.729의 복호화를 거치고 다시 PSOLA를 통해 음성의 피치 주기를 2배로 늘려주어 원음성을 합성하게된다. 기존의 Bkbp의 전송율을 갖는 G.729는 음성의 크기가 반으로 줄어 부호화되므로 전송율이 4kpb로 줄어들게 된다. 실험의 평가는 MOS 테스트를 통해 수행되었으며 4kbp에서 MOS값이 3.37정도로 측정되었다. 또한 처리해야할 음성의 길이가 줄어들게 되므로 계산시간도 줄어들게 된다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.8
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• pp.797-806
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• 2008

In a double-passage cascade apparatus, only two blades are installed in order to increase the accuracy of experimental result by applying bigger blade than the size of multi-blades on the same apparatus. However, this causes difficulties to make correct periodic condition. In this study, sidewalls are designed to meet periodic condition without removing the operating fluid or adjusting tail boards. Surface Mach number on the blade surface is applied to a responsible variable, and 12 design variables which are related with sidewall profile control are selected. A gradient-based optimization is adopted for wall design and CFX-11 is used for the internal flow computation. The computed result shows that it could obtain the same flow structure by modifying only the sidewalls of the double-passage cascade apparatus.

• Korean Journal of Optics and Photonics
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• v.9 no.1
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• pp.9-14
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• 1998

We present a simple method of determining the absolute order of moire fringes formed by the moire shadow topography with a criss-crossed grating. Two experimental methods in this topography are proposed and demonstrated; one is to change the ratio of x and y pitches in a criss-crossed grating after fixing the position of a light source and a camera, and the other is to change the position of a light source and a camera after fixing the ratio of x and y pitches in a criss-crossed grating.