대역확장 및 잡음제거를 이용한 음질 개선 연구

Abstract

In the first part, A search-free codebook mapping algorithm for bandwidth extension in G.729 compressed domain is introduced. We design a wideband line spectrum pair (LSP) codebook which is coupled with the same index as the LSP codebook of the G.729 speech codec. The received narrowband LSP codebook indices are used to directly induce wideband LSP codewords. Thus, the proposed scheme eliminates codebook search processing to estimate the wideband spectrum envelope. Experimental results show that the WMOPS complexity with the search-free codebook mapping process was reduced by 32% when compared to conventional codebook mapping. The complexity reduction can be obtained with no degradation in speech quality In the second part, we present a reduced complexity codebook search method for the codebook-based speech enhancement. The reduction is achieved by using a preliminary test that reduces the necessary speech codebook search range without degrading the enhancement performance. The test is performed based on a weighted MSE and a SNR adaption function. Artificial bandwidth extension (ABE) using search-free codebook is also applied to regenerate high frequency components and add those components to the narrowband enhanced speech signal. Experiment results show that the WMOPS complexity of enhancing narrowband noisy speech was reduced by 25% when comparing with the exhaust full search.