MPEG-4 HE-AAC中耦合編碼之設計

Abstract

SBR的耦合編碼機制乃藉由轉換資料的紀錄方式，以去除資料的相關性，達到節省位元的目的。然而，礙於耦合編碼的先天限制，若干原先獨立的資訊必須被雙聲道共用。由於資訊的共用，產生兩項關係到品質的設計議題，其中包含時頻格子與啾聲參數。再者，量化處理所造成的品質衰退的風險，也必須進一步的審視。本論文考慮可能產生的人工缺陷，來考量共用參數的決定，並提出一個兼顧高頻品質及需求位元數的耦合轉換方法。在品質的量測上，除了主觀的聆聽評量之外，並採用ITU所發展的PEAQ測試系統來評估音訊壓縮後的改良程度。

The coupling coding in SBR is adapted to transform the data domain to de-correlation and save more bits. However, because of the inherent constraint of the coupling coding, some side information need to be shared by the stereo channels. There are two considerable issues related to quality due to the sharing, including the determining of the shared T/F grid and the shared chirp factor. On the other hand, the quantization process causes of the risk of quality degradation also need to be inspected. This thesis considers the possible artifacts to examine the decision of the shared parameter, and proposes a coupling decision method for the tradeoff between high band quality and demand bits. Both subjective and objective tests are conducted to check the quality improvement. The objective test measures used is the recommendation system by ITU-R Task Group 10/4.