AES-EBUSpecification(IEC60958-4AudioDataFormat)最新音频标准,做音频必备的标准

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SPECIFICATION OF THE DIGITAL AUDIO INTERFACE

(The AES/EBU interface)

Tech. 3250-E - Third edition 2004

CONTENTS

1. Scope...................................................................................................................................................................2

2. Interface format....................................................................................................................................................2

2.1. Terminology.................................................................................................................................................2

2.2. Structure of format........................................................................................................................................3

2.3. Channel coding.............................................................................................................................................5

2.4. Preambles.....................................................................................................................................................5

2.5. Validity bit ...................................................................................................................................................6

3. User data format...................................................................................................................................................6

4. Channel status format...........................................................................................................................................6

5. Interface format implementation .........................................................................................................................12

5.1. General.......................................................................................................................................................12

5.2. Transmitter .................................................................................................................................................12

5.3. Receivers....................................................................................................................................................13

6. Electrical requirements.......................................................................................................................................13

6.1. General characteristic..................................................................................................................................13

6.2. Line driver characteristics ...........................................................................................................................14

6.3. Line receiver characteristics........................................................................................................................15

6.4. Connectors .................................................................................................................................................16

Appendix 1 Generation of the CRCC (Byte 23) for channel status...............................................................................17

Appendix 2 AES/EBU signals on Structured Wiring...................................................................................................19

Bibliography..............................................................................................................................................................20

European Broadcasting Union

Ancienne Route 17A, CH-1218 Grand-Saconnex (Geneva) Switzerland

tech 3250 EBU - Specification of the digital audio interface

Specification of the digital audio interface

(The AES/EBU interface)

1. Scope

This document specifies a recommended interface for the serial digital transmission of two channels of

periodically sampled and linearly represented digital audio data in a broadcasting complex, up to a distance of a few

hundred metres,

Although this transmission specification is independent of sampling frequency it is intended that the interface

be primarily used at 48 kHz, as this is the recommended sampling frequency for use in broadcasting studios (CCIR

Recommendation 646).

The document does not cover connection to any common carrier equipment nor does it specifically address any

of the questions relating to the synchronising of large systems, although by its nature the format permits easy

synchronisation of receiving devices to the transmitting device.

Specific synchronisation issues are covered in document AES 1l-l991.

Note 1: In this interface specification for broadcasting studio use, mention is also made of an interface for

consumer use. The two interfaces are not identical.

Note 2: An engineering guideline document to accompany this interface specification is in course of

preparation by the EBU.

2. Interface format

2.1. Terminology

For the purpose of this specification the following definitions of terms apply.

2.1.1. Sampling Frequency

The sampling frequency is the frequency of the samples representing an audio signal. When more than one

audio signal is transmitted through the same interface, the sampling frequencies shall be identical.

2.1.2. Audio sample word

The audio sample word represents the amplitude of a digital audio sample. Representation is linear in 2's

complement binary form. Positive numbers correspond to positive analogue voltages at the input of the analogue to

digital converter (ADC). The number of bits per word can be specified from 16 to 24 in two coding ranges (less than or

equal to 20 bits and less than or equal to 24 bits).

2.1.3. Auxiliary sample bits

The four least significant bits (LSB) can be assigned as auxiliary sample bits and used for auxiliary information

when the number of audio sample bits is less than or equal to 20.

2.1.4. Validity bit

This bit indicates whether the audio sample bits in the sub-frame (time slots 4-27 or 8-27 depending on the

audio word length as described in Section 2.2.1.) are suitable for conversion to an analogue audio signal.

EBU - Specification of the digital audio interface tech 3250

2.1.5. Channel status

The channel status carries, in a fixed format derived from the block (see Section 2. 1. 11.), information

associated with each audio channel, which is decodable by any interface user.

2.1.6. User data

The user data channel is provided to carry any other information.

2.1.7. Parity bit

The parity bit is provided to permit the detection of an odd number of errors resulting from malfunctions in the

interface.

2.1.8. Preambles

Preambles are specific patterns used for synchronisation. There are three different preambles (see Section 2.4.).

2.1.9. Sub-frame

The sub-frame is a fixed structure used to carry the information described in Sections 2.1.1. to 2.1.8. (See

Sections 2.2.1. and 2.2.2.).

2.1.10. Frame

The frame is a sequence of two successive and associated sub-frames.

2.1.11. Block

The block is a group of 192 consecutive frames. The start of a block is designated by a special sub-frame

preamble (see Section 2.4.).

2.1.12. Channel coding

The channel coding describes the method by which the binary digits are represented for transmission through

the interface.

2.1.13. Unit interval UI

Shortest nominal time interval in the coding scheme

2.1.14. Interface jitter

Deviation in timing of interface data transitions (zero crossings) when measured with respect to an ideal clock

2.1.15. Intrinsic jitter

Output interface jitter of a device that is either free running or is synchronized to a jitter-free reference

2.1.16. Jitter gain

Rate of transmission of frames

2.2. Structure of format

2.2.1. Sub-frame format

Each sub-frame is divided into 32 time slots, numbered from 0 to 31 (see fig 1)

Time slots 0 to 3 (preamble) carry one of the three permitted preambles (see Fig. 2) (see Sections 2.2.2. and

2.4; see also Fig. 2).

Time slots 4 to 27 (audio samples word) carry the audio sample word in linear 2's complement representation.

The most significant bit (MSB) is carried by time slot 27.

When a 24-bit coding range is used, the LSB is in time slot 4 (see Fig. 1a).

tech 3250 EBU - Specification of the digital audio interface

When a 20-bit coding range is sufficient, time slots 8-27 carry the audio sample word with the LSB in time slot

8. Time slots 4 to 7 may be used for other applications. Under these circumstances, the bits in the time slots 4 to 7 are

designated auxiliary sample bits. (See Fig. 1b)

If the source provides fewer bits than the interface allows (either 24 or 20) the unused LSB shall be set to

logic “0”.

(a)

0 3 4 27 28 29 30 31

Preamble

LSB

24-bit audio sample word

MSB

Validity bit User data

bit

Channel

status bit

Parity bit

(b)

0 3 4 7 8 27 28 29 30 31

Preamble

Auxiliary

sample bits

LSB

20-bit audio sample word

MSB

Validity bit User data

bit

Channel

status bit

Parity bit

Fig. 1 – Sub-frame format for audio sample words of

24 bits (top) and 20 bits (bottom).

Time slot 28 (validity bit) carries the validity bit associated with the audio sample word (see Section 2.5).

Time slot 29 (user data bit) carries one bit of the user data channel associated with the audio channel transmitted

in the same sub-frame (see Section 3).

Time slot 30 (channel status bit) carries one bit of the channel status information associated with the audio

channel transmitted in the same sub-frame (see Section 4).

Time slot 31 (parity bit) carries a parity bit such that time slots 4 to 31 inclusive will carry an even number of

ones and an even number of zeros (even parity).

Note: The preambles have even parity as an explicit property.

2.2.2. Frame format

A frame is uniquely composed of two sub-frames (see Fig. 2). The rate of transmission of frames corresponds

exactly to the source sampling frequency.

The first sub-frame normally starts with preamble "X", however the preamble changes to preamble "Z" once

every 192 frames. This defines the block structure used to organise the channel status information. The second sub-

frame always starts with preamble “Y”.

The modes of transmission are signalled by setting bits 0 to 3 of Byte 1 of channel status.

Channel 1

Channel 2

Channel 1

Channel 2

Channel 1

Channel 2

Sub-frame 1

Sub-frame 2

Frame 1

Frame 191

Frame 0

Start of

block

Fig. 2 - Frame format

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