GY/T 187-2002Serial multichannel audio digital interfance (English PDF)

Foreword

This standard is equivalent to AES10-1991 (ANSI S4.43-1991) "Multi-channel Audio Digital Serial Interface", English name. Serial multichannel audio digital interface (MADI).

This standard was developed for the design, production, acceptance, operation, maintenance, and use of multi-channel audio digital serial interfaces and related equipment systems.

Use, especially multi-channel digital audio program production and exchange, and then improve the broadcast quality and level, providing a technical basis.

Appendix A to this standard is an informative appendix.

This standard is under the jurisdiction of the National Radio and Television Standardization Technical Committee.

This standard was drafted. Central People's Broadcasting Station.

1 Scope

This standard specifies the data composition and electrical characteristics of the multi-channel audio digital serial interface (MADI).

This standard applies to linear or coaxial cable or fiber optic cable. The sampling frequency ranges from 32kHz to 48kHz (± 12.5%).

56-channel digital audio serial transmission with a resolution of 24 bits per channel (see Figure 1).

This standard only supports point-to-point connections from a transmitter to a receiver.

2 Normative references

The clauses in the following documents have become the clauses of this standard after being referenced. For dated references, all subsequent Neither amendments (excluding errata) or revised versions are applicable to this standard, however, parties who have reached an agreement under this standard are encouraged to study is the latest version of these files available? For undated references, the latest version applies to this standard.

GY/T 158-2000 studio digital audio signal interface

3 Terms and definitions

The following terms and definitions apply to this standard.

Audio sample data

An audio signal that is periodically sampled, quantized, and digitized in two's complement form.

Channel

A set of audio sample data corresponding to a signal transmitted within any period of the sampling frequency of the data source, which is accompanied by other Data bits.

Two-channel format

GY/T 158-2000 bit, block and sub-frame structure (without preamble).

Frame

Numbered 56-channel sequence from 0 to 55, each frame contains the audio sample data transmitted in any sampling period Processing and related data. Start with the first bit of channel 0 as the frame.

Link

Connection of a single serial multi-channel audio digital transmitter and a single multi-channel audio digital receiver.

4 Format

28 GY/T 158-2000 V significant digits 0 = true

29 GY/T 158-2000 U User data bit 0 = true

30 GY/T 158-2000 C status data bit 0 = true

31 GY/T 158-2000 P Parity (except bits 0 to 3) Even parity

Table 2 Bits 2 and 3 (compatible with GY/T 158-2000)

Bit 2 and Bit 3 2 channel format description 0 0 Format 2 A channel 0 1 Format 1 A channel block start status 1 0 Format 3 B channel 1 1 Format 4a B channel block start status a Not available for every GY/T 158-2000 Coding diagram for encoding, the 32-bit channel data is divided into 8 words in groups of 4 bits, as shown in Table 3.

Each 4-bit (4B) word is encoded into a 5-bit word, see Table 4.

Every 5 bit (5B) words are transmitted from the left, see Table 5.

The coding scheme allows a low-current DC bias to remain on the link. Although the link signal is not DC, the audio signal can be can contain DC. Figure 4 shows the link transmission format of a channel. For clarity, Appendix A illustrates the encoding of a single channel word process.

Table 3 Word structure

Word channel data bits 2 89 ..

7 .. 31

Table 4 4B/5B coding

4-bit data 5-bit coded data

Table 5 Arrangement of data transmission within words

Word channel connection bit word channel connection bit

4.3.1 Sync Signal

A synchronization signal 11000 10001 should be inserted in the data stream at least once per frame to ensure synchronization between the transmitting end and the receiving end. Should be enough the synchronization signal and the encoded data word are interleaved into the frame to meet the requirements of the link. The synchronization signal is transmitted from the left.

The synchronization signal can only be inserted at the 40-bit channel boundary, and transmitted between the channels, the idle interval or both at the last channel of each frame After sending, it can be inserted repeatedly. The placement order of the synchronization signals is not specified. Figure 5 shows several possible placement positions of the synchronization signals.

Figure 5 Some allowed sync signal positions

4.3.2 Transmission sequence in any bit order, the left symbol on the figure is always transmitted first in time.

4.3.3 Non-Return-to-Zero Inversion Link channel data is transmitted using non-return-to-zero phase-inversion non-polarity coding. Each high-level bit is expressed in steps based on the previous bit.

As shown, each low-level bit is represented by no step. Therefore, 1 is represented by a high-low or low-high step of the level, while 0 is represented by a continuous High or persistently low.

Note. For examples of non-return-to-zero reversion, see Appendix A.

5 Sampling frequency and bit rate

5.1 Sampling frequency the link operates at a nominal sampling frequency range of 32kHz to 48kHz and can operate within its ± 12.5% frequency range.

It can also accommodate higher sampling frequencies (such as 96kHz) when using two or more channels per audio sample on the link.

5.2 Link transmission rate the link transmission rate should be 125Mbit/s, regardless of the sampling frequency or the number of active channels.

Note. The error of this 125Mbit/s link transmission rate should be ± 10-4.

5.3 Data transmission rate the data transmission rate should be 100 Mbit/s. The difference between the data transmission rate and the link transmission rate is due to the coding design (see 4.3.1).

5.4 Maximum usage data rate with a sampling frequency of 48kHz × (1 12.5%), the maximum usage data rate of the 56 channels is 96.768 Mbit/s.

5.5 Minimum usage data rate with a sampling frequency of 32kHz × (1-12.5%) for the 56 channels, the minimum usage data rate is specified as 50.176 Mbit/s.

6 Sync

This part includes the synchronization of a master synchronization signal at the receiving end and the transmitting end, which is not only applicable to the master-slave connection.

Channel 0 Channel 1 Channel 2 Channel N Channel N 1 Channel N 2 Channel 54 Channel 55 Sync Sync Channel 0 (next frame) Start of frame

6.1 Sync signal

The main synchronization signal should be assigned to each receiving end and transmitting end separately. The synchronization signal should be consistent with GY/T 158-2000.

6.2 Sampling timing

The sampling timing information is not considered to be carried on the link. The precise timing of connected devices is controlled by a separately assigned master synchronization signal, not by multi-pass Audio digital interface is provided.

6.3 Transmission frame start time the start time of the frame output from the transmitting end should be within ± 5% of a sampling period.

The reference time for the number definition is determined.

6.4 Receive frame start time the receiving end should be able to correctly demodulate a signal that changes within ± 25% of a sampling period.

The reference time for the step signal definition is determined.

7 Electrical characteristics the transmission medium shall be a 75ohm coaxial cable (see 7.1) or an optical cable (see 7.2).

In order to accurately simulate the normal transmission signal, the test is replaced by a pseudo-random code generator with a sequence length of at least 216-1.

The encoder inputs data and accesses it before the 4B/5B bit encoder.

7.1 Coaxial cable

7.1.1 Transmitter

7.1.1.1 Line driver

The line driver should have a single-ended output with an output impedance of 75ohm ± 2ohm. Connected actual circuits, such as emitter-coupled logic (Emitter-Coupled Logic) The connection between the signal transmitter and the coaxial cable is shown in Figure 6.

Figure 6 MADI Transmitter Line Driver

7.1.1.2 Average output After the line is terminated, the average output voltage relative to the signal ground should be 0 V ± 0.1V.

7.1.1.3 Peak output

After the line output terminal is terminated with a 75ohm resistor, its peak-to-peak output voltage should be between 0.3V and 0.6V.

7.1.1.4 Rise and fall times After the line output terminal is terminated with a 75ohm resistor, the rise and fall times measured at the 20% and 80% amplitude points should not be longer than 3ns.

At 1ns. The average relative timing difference of the amplitude points should not be greater than ± 0.5ns.

7.1.2 Receiver

When the eye diagram measured at the input meets the characteristics shown in Figure 7, the receiver should be able to correctly interpret the received signal.

150n

O/P 1

O/P 2

150n

IN4148 IN4148

IN4148IN4148

120R

100R 100R 10K

10K

68R

68R

120R

tnom = 8ns;

tmin = 6ns;

Vmax = 0.6v;

Vmin = 0.15v.

Figure 7 Eye diagram of maximum and minimum input signals

7.1.3 Cable

The coaxial cable used should have a characteristic impedance of 75ohm ± 2ohm, and the attenuation in the frequency range of 1MHz to 100MHz should be less than 0.1dB/m.

7.1.4 Connector

BNC connectors are used throughout the link. Couplings shall be used for coaxial cable connections.

7.1.5 Cable length

The cable length should be less than or equal to 50m. Equalization should not be used. The signal should be no worse than the eye diagram defined in Figure 7.

7.1.6 Example of Interface Circuit the connection between the coaxial cable and the balanced emitter-coupled logic signal can be achieved by a circuit as shown in FIG. 8.

7.1.7 Ground

The coaxial cable sheath should be grounded at the transmitting end. In order to minimize RF radiation, it is recommended that the coaxial cable should be directly fixed to the equipment on the box.

When the radio frequency is higher than 30MHz, the coaxial cable should be grounded and connected to the receiving end case. This connection is recommended as a coaxial cable connector housing Capacitively coupled to the receiver chassis. A suitable capacitor value is 1000pf. Capacitors should be low inductance, between 30MHz and 500MHz Has a sufficiently low impedance. The wire bonding length should be as short as possible. This prevents possible audio ground currents.

Figure 8 MADI buffer amplifier circuit diagram

7.2 Optical cable

To be determined.

Vmax Vmin

tmin

tnom

300R

100R

68R 68R

4K7

IN4148

75R

1000PF

10n

1/16V

RX (s)

1/16V

100R

300R

IN4148

4K7

10n

IN4148

IN4148

10K

IN4148

SP9680

IN4148

IN4148

IN4148

Appendix A

(Informative appendix) Link encoding example Assume the channel data words are as follows.

Bits. 0123 4567 8901 2345 6789 0123 4567 8901 Data. 1100 1010 0101 1111 0000 1100 0011 0000 After conversion.

-------------------------------------------------- -Word 4-bit data 5-bit coded data 3 1111 11101 4 0000 11110 5 1100 11010 6 0011 10101 7 0000 11110 the transmitted bitstream is.

Bits. 01234 56789 01234 56789 01234 56789 01234 56789 Link (NRZ code). 11010 10110 01011 11101 11110 11010 10101 11110 Link (NRZI code). 01001 10010 00110 10100 10101 10110 01100 10101 Transmission direction Note. The NRZI bitstream shown can also be inverted, with polarity depending on the last bit before.