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第三章语音信号的压缩编码 PowerPoint PPT Presentation


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语音信号的压缩编码是研究如何降低语音信号编码速率的问题。. 第三章语音信号的压缩编码. 以语音信号为例,模拟形式下带宽一般不到 4KHz ,经过调制后,所需传输带宽不会超过 8KHz 。. 一 . 压缩编码原因. 但是以 8KHz 抽样,并且每个样值用 8 位二进制代码表示时,即采用 A 率 13 折线 PCM 数字语音信号时,信息速率为 64Kbit/s 。. 频带利用率 = 传输速率 / 带宽. 利用二进制理想基带传输系统传输一路这样的数字语音信号。所占系统的最小频带宽度为 32KHz 。. 二 . 什么是语音压缩编码?.

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第三章语音信号的压缩编码

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4KHz8KHz

.


8KHz8A13PCM64Kbit/s

=/

32KHz


  • .

64Kbit/s


.


1


16------64kbit/s

PCM

ADM

ADPCM

APC


  • 2.

4.8kbit/s

  • )

  • :LPC


+

3.

4----16kbit/s


3.1ADPCM

  • 3.1.1DPCM

  • 1.

N




+

+

x(n)+d(n)c(n)d(n)x(n

-

x(n)x(n)


x(n)n

x(n)

d(n)=x(n)-x(n)

1d(n)

2x(n)


DPCM

1DPCM

  • DPCM


  • ,1/TsSt, .N


:


2N


N

t=nTs



3DPCM


x(n)


4DPCM

x(n)=x(n)+d(n)

  • d(n)=x(n)-x(n)

e(n)=x(n)-x(n)

=[d(n)+x(n)]-[x(n)+d(n)]

=d(n)-d(n)


=

=

GP<1

GP>1


GP DPCMPCM

PCM



d(n)=x(n)-x(n)

d(n)

x(n)


  • .

  • .

  • .

  • 3.1ADPCM

  • 3.3.1DPCM

  • .

  • .

  • .DPCM

  • 1.2.3.DPCM4.DPCM


3.1ADPCM

1DPCM+

DPCMADPCM

2


3.

  • ADPCM,:

a:

b:

,


1.1

1.

(1).

(x(n)

a:

X(n)

d(n)

d(n)

+

X(n)

+

Xn

PZ

X(n)


b:P(z)

N

X(n)=


Z


H(Z)

c:

x(n)

d(n)

+

X(n)

x(n)


2

2

=E [x(n)]+E[x(n-1)]-2E[x(n)x(n-1)]

2

=2E [x(n)]-2E[x(n)x(n-1)]

=

=

=


2

2

=E [x(n)]+h1E[x(n-1)]-2h1E[x(n)x(n-1)]

2

2

h1

+

N=1

X(n)=

h1x(n-1)

d(n)=x(n)-h1x(n-1)

E[d (n)]=

2

2

=E{[x(n)- h1x(n-1)] }

2

=

-

=

h1


h1opt=p1

N=1


2

2

=E[d (n)]

=E{[x(n)- h1x(n-1)-h2(n-2)] }

b.N=2

d(n)=x(n)-h1x(n-1)-h2x(n-2)

h1,h2



2

=E[d (k)]

CN





2.

  • 1)

R(i),

:


2

{hi(n)}E[d(n)],{hi(n)}{hiopt(n)}.

2


LMS


()


+

1.2

1


2

  • d(n)

:


3

AQF)


(AQB)


Jayant

=

M| [I(n-1)] |-------


  • LDPCMM


,,:

-----------------



DLQ


yu(n)

y(n)

yl(n)

d(n)


32kb/sADPCM

Ccittg.721PCM32kb/sADPCM

1ADPCMSNRPCMPCM

2MOS3.5

30.001


1DPCMh1=1p1

Gp

2h1=h1optGpopt


2 R1R2DPCMGpopt


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