本論文主要是以MPEG-1 Layer III（MP3）音訊壓縮編碼器之實現與研究為主，並針對MP3 在低位元率時的缺失，提出編碼效能分析及音質的改善。首先，我們利用低通濾波器與適應性頻譜截斷法將MP3 低位元率編碼的缺點加以修正；然後，再針對上述方法之缺點加以改良，提出高頻補償法以補償高頻缺失的部分，使得MP3 音訊壓縮編碼器於低位元率的編碼效能及音質更加完善。

The research of this thesis is mainly focused on study and implementation of MPEG-1 Layer III (MP3) for low bit-rate applications. First, we propose a lowpass filter approach and its daptive spectrum reduction method to reduce the defeat of the MP3 codec in low bit-rate applications. Both lowpass and spectrum reduction algorithms will sacrifice the high frequency components of audio signals. To improve the high frequency performance, we further suggest a high frequency compensation method to make up the quasi-harmonics of high frequency spectrum. By using spectrum reduction
and quasi-harmonic compensation method, the MPEG-1 Layer III audio coder can achieve a high perceptual quality for low bit-rate applications.

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