第五章 语音信号的激励源参数分析

Chapter 5

Estimation of Excitation Parameters

1. 激励源模型

2. 基音周期估计

Ⅰ.Excitation Source Models

1-1 Ideal Excitation Source

x(n)A(z)e(n)1x(n)A(z)E(z)A(z)X(z)X(z)1A(z)E(z)

If e(n) were encoded directly , high bit rate would be required.

1-2 Binary Excitation Model

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Digital Processing of Speech Signal Chapter 5 Estimation of Excitation Parameters PitchImpulse Train GeneratorV/UA(z) Random Noise Generator Encoded bit rate is low, but the naturalness of reconstructed speech is not good.

1-3 Mixed Excitation Models ( Itakura & Saito, 1968)

Pulse GeneratorV1 NoiseA(z) GeneratorRe(0)U 2

Digital Processing of Speech Signal Chapter 5 Estimation of Excitation Parameters

1VU=1-V0.250.500.18Re(n)Re(n)Re(0)

在3－15ms内搜寻

Re(0)的峰值位置np

V0.25Re(n)URe(0)V0.18U1001VoicedUnvoiced

0.18Re(np)Re(0)0.25,V01

1-4 Multiband Excitation Model（多带激励）

将话带语音分成若干个子带，然后针对每个子带进行清浊音判决，因此可以更好的建模激励信号。

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Digital Processing of Speech Signal Chapter 5 Estimation of Excitation Parameters

1-5 Baseband Excitation Model

A(z)e(n) BasebandHigh ExtractionFrequency1RegenerationA(z) LPAnalysis Baseband Extraction:

e(n) LPFb(n)Decimation (W)(B) L:1fc1000HzFs8kHz,L4BWL1kHz

HFR:

Interpolation 1:LHFRHPF 1-6 Multi-pulse Excitation Model

Bishnu S. Atal，1982, ICASSP

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Digital Processing of Speech Signal Chapter 5 Estimation of Excitation Parameters

e(n)g1g20n1n2nng3Mn3gM

e(n)Mgi(nni),M:48/5msi1

Regular-pulse Excitation applied in GSM vocoder

1-7 Code Excitation Model

x(n) e(n)二次残差F(z)P(z)

1024*4010bit/40CODEx(n)BOOKP(z)F(z)STPLTP

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Digital Processing of Speech Signal Chapter 5 Estimation of Excitation Parameters

Shorttermpredictor:F(z)a(k)z,20mskk1IpLongtermpredictor:P(z)c(i)ziI(T0i),5ms。I0orI1

Manfred R. Schroeder and Bishnu S. Atal , 1985, ICASSP

CELP：Code Excited Linear Prediction 码激励线性预测

G.728 LD－CELP 16kbps

G.729 CS－ACELP 8kbps IP Phone

G.723 ACELP 5.3kbps

Ⅱ.Pitch Period Estimation

2-1 Introduction

·Definition: Fundamental frequency(and close.

F0) is the rate at which the vocal folds open

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Digital Processing of Speech Signal Chapter 5 Estimation of Excitation Parameters

Reciprocal of

F0 is the Pitch period

T01F0

·取值范围： 25－2.5ms (40－400Hz)

·重要性：基音频率是基本的语言声学参数。可用于语音识别，说话人识别，语音合成，语音编码。

·汉语中的四声取决于

F0的变化。

5F05－543－5mamma35－1妈麻a马m骂a22－1－41

·估计

F0的困难：

⑴过渡段语音难分。V/U

⑵

F0的变化范围大

⑶声道对激励参数估计的影响

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Digital Processing of Speech Signal Chapter 5 Estimation of Excitation Parameters

·Types of Pitch Detectors

⑴Time－Domain

⑵Frequency－Domain

⑶Hybrid

2-2 Clipping Autocorrelation Pitch Detector

y(n)x(n)CL,x(n)CLx(n)中心y(n)C削波Ly(n)0CLx(n)0,x(n)CLx(n)CL,x(n)CL

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Digital Processing of Speech Signal Chapter 5 Estimation of Excitation Parameters

y(n)1CL,x(n)CLx(n)三电平削y(n)CLy(n)0,x(n)CL波0CLx(n)－1CL,x(n)CL

N1kR(k)x(n)x(nk),k0,1,k1,,k2n0k120,(startpoint)2ms500HzIpk0.3,Uk)20ms50Hz,2200,(endpointR(0)0.3,VT0Ipos

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Digital Processing of Speech Signal Chapter 5 Estimation of Excitation Parameters

2-3 Simplified Inverse Filtering Tracking (SIFT) Algorithm

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Digital Processing of Speech Signal Chapter 5 Estimation of Excitation Parameters

900Hzs(n)LPFDecimationx(n) 5:1A(z)e(n)1fs=10kHz1z Peak PickwH(n)抛物线 内插 1：5LP Analysis p=4T0IpkComputee(n) R(k)IpkDecision RuleVUT00

Ipos基音周期范围：

5kL6,(61)2.5ms400Hz105kH32,(321)15.5ms64.5Hz10

判别Ipk的方法——可变门限法

T015.5msT09msT02.5msIpk0.315R(k)Ipk0.35R(k)Ipk0.7R(k)

T01T03T02(T01,T02,T03表示连续3帧基音周期)2语音流中基音周期延时判决：

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Digital Processing of Speech Signal Chapter 5 Estimation of Excitation Parameters

ModifiedAutocorrelation:R(k)x(n)x(nk)k0N1N取2倍T0,也可取最长的T0或用自适应方法。2-4 Cepstral Method

s(n)EnframeFs=10kHz51.2ms/framewH(n)Z(n)FFTlogIFFTU/High V/LowVPeaksionT0IposPickIposRuleUT00IpkDeci-E(n)Silence?No ComputeCepstrum C(n)Peak PickC(n)>T?NoVNoZ(n)>t?YesNext FrameYesYesVU

C(n)IpkIpos2-5 AMDF(短时平均幅度差函数)

n

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Digital Processing of Speech Signal Chapter 5 Estimation of Excitation Parameters

2-6 基音检测的后处理

平滑(中值平滑，线性平滑，组合平滑，高斯平滑)

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Digital Processing of Speech Signal Chapter 5 Estimation of Excitation Parameters

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