• The Journal of the Acoustical Society of Korea
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• v.25 no.4E
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• pp.154-158
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• 2006

In this paper, we suggest a noise estimation method for speech enhancement in nonstationary noisy environments. The proposed method consists of the following two main processes. First, in order to receive fewer affect of variable signals, a best fitting regression line is used, which is obtained by applying a least squares method to coefficient magnitudes in a node with a uniform wavelet packet transform. Next, in order to update the noise estimation efficiently, a differential forgetting factor and a correlation coefficient per subband are used, where subband is employed for applying the weighted value according to the change of signals. In particular, this method has the ability to update the noise estimation by using the estimated noise at the previous frame only, without utilizing the statistical information of long past frames and explicit nonspeech frames by voice activity detector. In objective assessments, it was observed that the performance of the proposed method was better than that of the compared (minima controlled recursive averaging, weighted average) methods. Furthermore, the method showed a reliable result even at low SNR.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.9
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• pp.99-108
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• 1997

An efficient wavelet packet algorithm to find wavelet packet quickly is presented in this paper. The top-down method maximizing the transform coding gain that is obtained from the second moment of the band is used to divide the subbands into wavelet tree. The bit allocation for each band in the tree is performed in proportion to its variance. Bands are coded by the lossless coding algorithm called the bit plane run length coding(BPRLC) and uniform quantizer. The proposed algorithm is compared with of the single tree algorithim proposed by Ramchandran and Vetterli. To verify the efficiency of our algorithm, simulations are jperformed using several sets of images. The results show us that our method reduces the execution time by about forty percent of that required by the single tree method while maintaining the comparable reconstructed image qualities.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.5
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• pp.1096-1108
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• 1996

In this paper, we propose a temporal adaptive tranform 3D SBC coder with motion compensation, exploiting redundancy in the temporal domain. We propose a temporal adaptivity measure, by which the R-D optimal temporal transform can be chaosen. The base temporal subband frame is coded using H.261-like MC-DCT coder, while the higher temporal subband frames are coded using the 2D adaptive wavelet packet bases, considering the various energy distribution which results from the temporal variation. In encoding the subbands, we employ adaptive scanning methods, uniform step-size quantization with VLC, and coded/not-coded flag reduction technique using the quadtree structure. From the simulation results, the proposed adaptive 3D subband coder shows about 0.29~3.14 dB gain over the H.261 and the fixed 3D subband coder techniques.