低延遲話音編碼算法的增益優(yōu)化與混合窗設(shè)計(jì)
Optimizing Gain and Designing Hybrid Window of LD-CELP
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摘要: G.728標(biāo)準(zhǔn)將增益濾波器的偏移不適當(dāng)?shù)靥幚沓沙?shù)32dB,相當(dāng)于將20～30ms內(nèi)短時(shí)平穩(wěn)的語(yǔ)音信號(hào)不適當(dāng)?shù)匕凑麄€(gè)時(shí)間軸上的平穩(wěn)信號(hào)對(duì)待。對(duì)增益濾波器的改進(jìn)必然涉及優(yōu)化混合窗。該文提出一種估計(jì)平均分段信噪比的方法用來(lái)設(shè)計(jì)混合窗參數(shù),并導(dǎo)出激勵(lì)增益的精確表示。以此為基礎(chǔ),將Jayant的自適應(yīng)量化與G.728的增益預(yù)測(cè)結(jié)合起來(lái),提出一種適合于設(shè)計(jì)低時(shí)延碼激勵(lì)線性預(yù)測(cè)(LD-CELP)的增益碼書(shū)的方案。用此方法,激勵(lì)的精確值經(jīng)自適應(yīng)預(yù)測(cè)和量化后,3bit自適應(yīng)量化和4bit自適應(yīng)量化分別比G.728的固定量化有0.5dB和6dB的信噪比的改善。當(dāng)采用4bit自適應(yīng)量化和64碼字的波形碼書(shū),比G.728復(fù)雜性降低20%,同時(shí)信噪比提高1dB。
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關(guān)鍵詞:
- 語(yǔ)音處理; G.728; LD-CELP; 增益濾波; 混合窗
Abstract: The offset of gain filter is dealt unsuitably with a constant 32dB in G.728 standard. That is, the short-term stationary speech signal during the duration 20~30ms is unsuitably supposed as stationary at whole time axis. It is necessary to design optimizing hybrid window for improving gain filter. In this paper, the exact expression of excitation gain is derived and an estimation method of SNRav used to optimize the parameters of hybrid window is presented. On the basis of above, this paper combines the Jayant adaptive quantization and G.728s gain prediction to propose a scheme fit for designing gain codebook of Low Delay Code Excited Linear Prediction(LD-CELP), in which the exact gain value is adaptively predicted and quantized. In this method, for adaptive quantization gain of 3 bit and 4 bit, the SNR increases by 0.5 and 6 dB separately than that of G.728. If adopting 4 bit adaptive quantization and the shape codebook of 64 codevectors, the G.728 complexity can reduce by 20% while SNR has 1 dB improvement. -
CCITT. Recommendation G.728, Coding of speech at 16kbit/s using low-delay code excited linear prediction[S]. Geneva,1992-9.[2]CHEN J H. A robust low-delay CELP speech coder at 16 kb/s [D/B]. Advances in Speech Coding, 1991:30 - 32.[3]Zhang G, Xie K M, Zhang X Y, Huangfu L Y. Optimizing gain codebook of LD-CELP[C]. Proceeding of ICASSP2003, Hong Kong, 2:149 - 152.[4]皇甫麗英,張剛,等.改進(jìn)G.728語(yǔ)音編碼算法的增益濾波[J].太原理工大學(xué)學(xué)報(bào),2002,33(3):232-233.[5]Jayant N S. Adaptive quantization with a one-word memory[J].BellSyst. Tech. J., 1973, 52: 1119- 1144.[6]Cummiskey, Jayant, et al.. Adaptive quantization in differential PCM coding of speech[J]. Bell Syst. Tech. J., 1973, 52:1105- 1118. -
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