- 學位論文
ACELP語音編碼器之混合候選型快速搜尋法
A HYBRID CANDIDATE SCHEME FOR FAST ACELP SEARCH
摘要
語音訊號的編解碼方式可說是經過一連串的技術進步與汰換，如此一連串的進步就是希望讓輸出的語音品質在不同的環境與應用下，跟有限的資源與市場需求達到完美的搭配妥協；而有限的成本資源往往與系統的運算複雜度（complexity）關係最為密切；以目前最被採用的ACELP語音編碼模式而言，其運算量大部份集中在代數碼本的搜尋運算上；因此如何在代數碼本上做快速且精確的搜尋運算就變得日漸重要。此也為本篇論文的主要目的。 本篇論文主要提供了一個快速且精確的代數碼本搜尋方案，此搜尋方案混合了之前曾被發表的兩種快速搜尋方案的特性，以形成另一種新的快速搜尋方案，我們通稱此方案為Hybrid scheme；而被混合的兩個快速搜尋方案分別是：出自國立成功大學電機工程學系的一篇被發表於電子電機工程師學會的文章（Candidate scheme for fast ACELP search, IEE, 2002），我們通稱此代數碼本搜尋方案為Chen’s scheme；另一個快速搜尋方案是出自本人學長的去年畢業論文，我們通稱此方案為Wang’s scheme，此快速搜尋方案正待投稿中。 我們採用1995年2月出自國際電信聯盟（ITU-T）的語音訊號編解碼標準G.729（fixed point version）來做為本論文實驗之代數碼本。實驗結果顯示，在降低運算複雜度與快速碼本搜尋的效能上，使用Hybrid scheme的確優於被混合的Chen’s scheme與Wang’s scheme；並且也保持了相當程度的語音品質。而在與depth-first-tree-search scheme做效能比較與細部分析後，也證明了Hybrid scheme的確具有可讓實務系統開發者彈性選擇或參考的存在價值與地位。
並列摘要
A manner of speech coding could be said to come over a series of advances and replacement of technology; and all of these are just for the perfect compatibility or trade-off between the finite resource and the marketing request; and the finite resource is usually closely related to system computational complexity. For an example of ACELP speech codec mode, a huge amount of computations are concentrated in the part of codebook search. Therefore, how to do a fast and accurate search on algebraic codebook becomes very important; and this is the main propose for this thesis. This thesis mainly supplies a fast and accurate scheme for codebook search; and this scheme is the mixture of the characteristics of two fast search schemes：One is from a paper of electrical engineering department of National Cheng Kung University [6], which is called “Chen’s scheme” in this thesis; and another one is from a graduation thesis of my senior classmate last year [32], which is called “Wang’s scheme” in this thesis. We called this innovated search scheme as “Hybrid scheme” in this thesis. We adopt the ITU-T G.729 codec standard as a sample for experience in this thesis. From the experience result, Hybrid scheme indeed has great performance better than that of two cooperated schemes, Chen’s scheme and Wang’s scheme for the performance of codebook search and the reduction of computational complexity; besides, it really preserves certain degree of speech quality. And after the complexity comparison and the detailed analysis for Hybrid scheme and depth-first tree search, we prove that Hybrid scheme does have its existing value for reference and the flexible selection for system developer.