ISO/IEC 11172-3:1993 - 数字音频编码标准

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"ISO/IEC 11172-3是1993年发布的一项国际标准，属于信息技术领域，特别关注于运动图像及其伴音的数字存储媒体编码，速率大约在1.5Mbit/s。这个标准的第三部分专注于音频编码。" ISO/IEC 11172-3是MPEG-1音频层标准的一部分，它定义了在有限带宽下高效编码音频信号的方法。这个标准对于数字音频广播、CD-ROM和VCD等早期数字媒体格式的普及起到了关键作用。MPEG-1音频层包括三个级别（Layer 1、Layer 2和Layer 3），其中Layer 3就是我们熟知的MP3格式。 1. **范围** (1.1 Scope): ISO/IEC 11172-3规定了用于数字存储媒体（如磁盘、光盘等）的运动图像及其伴音编码的规范，特别是在数据速率约为1.5Mbit/s时的音频编码。这意味着标准适用于需要在低带宽下传输高质量音频的情况。 2. **引用标准** (1.2 Normative references): 标准引用了其他相关技术规范，确保了与其他技术的兼容性和一致性。 3. **技术元素** (Section 2: Technical elements): - **定义** (2.1 Definitions): 这一部分提供了标准中使用的术语和概念的清晰定义，以便理解和应用。 - **符号和缩写** (2.2 Symbols and abbreviations): 列出了所有重要的符号和缩写，以便读者能准确理解标准内容。 - **位流语法描述方法** (2.3 Method of describing bitstream syntax): 描述了音频编码后的位流结构，这是解码器解析和重建音频信号的关键。 - **需求** (2.4 Requirements): 规定了实现该标准的系统或设备必须满足的技术要求。 4. **附录** (Appendices): 标准包含多个附录，如： - **A 图形** (A Diagrams): 提供了有助于理解标准工作原理的图表。 - **B 表格** (B Tables): 可能包含各种参数、配置选项或性能指标的列表。 - **C 编码过程** (C The encoding process): 详述了音频信号从原始形式到编码位流的转换步骤。 - **D 心理声学模型** (D Psychoacoustic models): 阐述了如何根据人类听觉系统的特性来优化编码，以达到更高的压缩比而不失真。 - **E 位错误敏感性** (E Bit sensitivity to errors): 讨论了位错误对解码效果的影响，并可能给出了错误检测和恢复策略。这个标准的实施对于音频压缩技术的发展产生了深远影响，特别是MP3格式，它极大地推动了数字音乐的广泛传播。通过高效的编码算法，MPEG-1音频层允许在有限的带宽下提供接近CD质量的音频体验，这在互联网和移动设备的早期阶段尤为重要。

ISOAEC

172-3: 1993

(E)

ISOAEC

2.2

Symbols and abbreviations

The mathematical operators

used

describe

this

International

Standard

are

similar

to those

used

the

progl-dmming language. However, integer division with truncation and rounding

are

specifically defined.

The bitwise operators are defined assuming twos-complement representation of integers. Numbering and

counting loops generally begin from

zero.

2.2.1

Arithmetic operators

Addition.

Subtraction

(as

a binary

operator)

negation

(as

a unary

operator).

Increment.

Decrement.

Multiplication.

Power.

Integer division with truncation

the

result

toward zero.

For

example, 714 and -71-4 are

truncated to

and -7/4 and

71-4

are truncated

-1.

Integer division with rounding

the nearest integer. Half-integer values are

rourided

away

from

zero

unless otherwise specified.

For

example

3/12

is rounded

and

-3//2

is rounded

-2.

Integer division with truncation

the result towards

-m.

Absolute value.

when

-x

when

Modulus operator. Defined only for positive numbers.

Sign(x)

x==o

-1

Nearest integer operator. Returns the ne‘uest integer value to the real-valued argument. Half-

integer values are rounded away from zero.

Sine.

Cosine.

Exponential.

Square root.

LogCarithm

base ten.

Logarithm

base e.

Logarithm

base

2.2.2

Logical

operators

Logical

OR.

Logical

AND.

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ISO Store order #: 539739/Downloaded: 2003-04-11

Single user licence only, copying and networking prohibited

ISOAEC

172-3:

1993

(E)

ISO/IEC

xpchof

Remainder polynomial coefficients, highest order

first.

(Audio)

sb Subband. (Audio)

sblimit

The number of the lowest sub-b<md for which no bits are allocated. (Audio)

scfsi Scalefactor selection information. (Audio)

switch-point-l

Number of scalefactor bald (long block scalefactor band) from which point on window

switching is

used.

(Audio)

switch-point-s

Number of scalefactor baud (short block scalefactor band) from which point on window

switching

used. (Audio)

uimsbf

vlclbf

Unsigned integer, most significant bit first.

Variable length code, left bit fust, where "left" refers to the order in which the VLC

codes

are

written.

window Number of the actual time slot

case of block_type==2,

window

2. (Audio)

The byte order of multi-byte words is most significant byte first.

2.2.7

Constants

3,'14159265358

...

e 2,'11828 182845

...

2.3

Method

describing bitstream syntax

The bitstream refrieved by the decoder is described in 2.4.1. Each

dztz

item

the bitstrean is

bold type.

It is described by

its

name, its length

bits, and a mnemonic for its type and order of transmissiion.

The action

~zused

by a decoded

dztz

element in a bitstrean depends

the value of that

element and

data

elements previously decoded. The decoding of the

dzta

elements

and

definition of the state variables

used in their decoding are described in 2.4.2. The following constructs are used to express the conditions

when

data

elemtmts are present, aid are in nonnal type:

Note this

syntax

uses the 'C'-code convention that a variable or expression evaluating

a non-zero value

equivalent

condition that is me.

while

(

condition

)

(

da ta-element

If the condition is true, then the group of

data

elements occurs next

the

daLi

stream. This repeats until the condition

not me.

...

The

dztiz

element always occurs at least once.

The

clam

element is repeated until the condition is not true.

do(

da ta-eleme nt

]

while

(

condition

)

...

(

condition)

(

If the condition is Vue, then the first group of

dat?

elements occurs

the

&?LI

stream.

data-element

the condition is not true, then the second

group

elements

occurs next

the dam stream.

else

(

da ta-eleme nt

...

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ISO Store order #: 539739/Downloaded: 2003-04-11

Single user licence only, copying and networking prohibited

ISOAEC

172-3:

1993

(E)

fol:

(exprl; expr2; expr3)

(

exprl is

expression specifying the initialization of the loop. Normally

data-elemen t

...

specifies the initial state of the counter. expr2 is

condition specifying

test

made before each iteration of

the

loop. The loop terminates when the condition

is not true. expr3 is

expression

that

is performed at the end of each iteration

of the loop, normally

increments

counter.

Note that the most common usage of this construct is

follows:

for

(

n; i++)

(

The group of

data

elements occurs

times. Conditional constructs

within the group of data elements may depend on the value of the

loop control variable i, which is set to zero for the first occurrence,

inaemented

one for

the

second occurrence, and

forth.

data-element

...

noted, the group of

data

elements may contain nested conditional constructs. For compactness, the

(

}

may

omitted when only one

data

element follows.

data-element [I

da ta-element

[

data-element [m][n]

dala-element [I][m][n]

data-element [m..n]

data-element

array of data The number of

dari?

elements is indicated by

the context.

dak?-element [n] is the n+lth element of

array of

daci.

data-element

[m][nl

is the m+l,n+l

element of

two-dimensional

'way

&?til.

&?ta-element [l][m][n] is the l+l,m+l,ntl

element of

three-dimensional

anay of

data.

is the inclusive range of bits between bit m and bit n in the data-element.

While the

syntax

is expressed in procedural terms,

should not be ilssumed that 2.4.3 implements

satisfactory decoding

procedure.

In particular, it defines

correct

and

error-free input bitsueam. Actual

decoders inust include a means to look for

SLW

codes

order to begin decoding correctly.

Definition of bytealigned function

The function bytealigned

returns 1 if the current position is

a byte

bound,ary,

that is the next bit in the

bitstream is the first bit

a byte. Otherwise

returns

Definition of nextbits function

Th€:

function nextbits

()

pennits comparison of a bit suing with the next bits to be decoded

the

bitstream.

Definition of next-start-code function

The:

next-start-code function removes .my zero bit

and

zero byte stuffing and locates the next

stat

code.

Syntax

No.

of bits Mnemonic

next-start-code0

(

while

(

!bytealignedo

)

while

(

nextbits()

'O000

O000

0000

0001'

zero-bit

'O'

zero-byte

'00000000'

This function checks whether the current position is bytealigned.

is not, zero stuffing bits are present.

Aftx

that any number of zero bytes may be present before the start-code. Therefore start-codes are always

byt1:aligned and inay

preceded by any

number

zero stuffing bits.

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