미세입자의 입경별 중금속 노출과 위해성평가

Abstract

[한글]

[영문]This thesis proposes a new method of improving the quality of High Efficiency Advanced Audio Coding (HE-AAC). HE-AAC encodes input signal by allocating bits to each scalefactor bands appropriately according to human ear’s psychoacoustic property. At low bitrate, however, insufficient bits are assigned to the bands which have relatively low energy. Such imbalanced bit allocation can cause sound quality degradation shch as musical noise. In the proposed method, a Linear Prediction (LP) module is combined with HE-AAC as a pre-processor which results in evenly distributed bit allocation and reduced musical noise. In its implementation, masking threshold of psychoacoustic model is normalized with the LP spectral envelope prior to quantization of the LP residual. In order to save bits, only long block frames with Extended Temporal Noise Shaping (ETNS) are used. Also quantization module is fitted to LP combined low bitrate HE-AAC. By this quantization module, LP residual signal can be coded appropriately without any loss of bits. Experimental results show that, proposed algorithm allocate bits appropriately for insufficient bits condition and improve the performance of HE-AAC.