MP3與AAC解碼器上的音訊修補方法

Abstract

由於位元率的限制，目前的音訊壓縮器，如MP3、AAC，會導致一些人為雜訊與缺失。本論文將考慮兩個問題。第一個是會造成知覺上“滑溜”噪音的頻譜凹陷現象。第二個是高頻截斷的問題，這會使聲音變悶。本論文提出可實現於音訊解碼器上的頻譜修補方法來改善這兩項缺失。這項技術可以置入MPEG1— Layer3 與 MPEG 2/4—AAC (Advanced Audio Coding) 解碼器來消除這些問題，並且不需要來自原始音訊上先前資訊的輔助。我們透過在多種編碼器與多樣的音訊種類上密集的實驗來驗證品質的改善以及可能的品質折損風險。此外採用ITU-R Task Group 10/4.的推薦系統來進行客觀的量測驗證。

Current audio encoders like MP3 or AAC leads to some artifacts due to the bit rate constraint. This thesis considers two artifacts. The first artifact is the unusual spectral valley which is perceptually heard as fishy noise. The second one is the spectrum clipping which leads to the muffling audio. This thesis proposes the spectrum patch method to handle the two artifacts in the decoders. The technique can be included in MPEG1— Layer3 and MPEG 2/4—AAC (Advanced Audio Coding) decoders to conceal the artifacts without prior information on the original audio tracks. Intensive experiments have been conducted on various encoders and audio tracks to check the quality improvement and the possible risks in degrading the quality. The objective test measures used is the recommendation system by ITU-R Task Group 10/4.