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GY/T 193-2003 English PDF

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GY/T 193-2003: Synchronization of digital audio system
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Basic data

Standard ID	GY/T 193-2003 (GY/T193-2003)
Description (Translated English)	Synchronization of digital audio system
Sector / Industry	Radio, Film & TV Industry Standard (Recommended)
Classification of Chinese Standard	M70
Classification of International Standard	33.160.30
Word Count Estimation	7,764
Date of Issue	2003-07-11
Date of Implementation	2003-08-01
Adopted Standard	AES 11-1997, IDT
Summary	This standard specifies the two sets of parameters. The first group is the digital audio data between the devices on the successful exchange performance requirements, the second group on the digital/analog and analog/digital conversion of the clock recovery performance requirements. This standard applies to the digital studio environment interconnect digital audio equipment, but also for the studio environment with an external device connected to the signal source and the receiver.

GY/T 193-2003: Synchronization of digital audio system

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Synchronization of digital audio system Digital audio system synchronization (AES11-1997, Synchronization of digital audio equipment in studio operations, IDT) 2003-07-11 release 2003-08-01 Implementation Published by the State Administration of Radio, Film and Television People's Republic of China Radio, Film and Television Industry Standard GY

Foreword

With the development of digital technology, the digitalization process of the radio and television industry is gradually accelerating, and analog devices have been replaced by digital devices. along with The increase of digital equipment will inevitably lead to the synchronization problem of digital audio systems. To this end, the "Digital Audio System Synchronization" standard needs to be developed. This standard is equivalent to AES11-1997 "Synchronization of Digital Studio Audio Equipment", which specifies the synchronization of digital studio audio equipment signal. This standard is under the jurisdiction of the National Radio and Television Standardization Technical Committee. This standard was drafted. Central People's Broadcasting Station. The main drafters of this standard. Liu Zhaohui and Song Bo. AES Preface This document is a revision of AES11-1991. It provides operational standards and guidance for users who need to synchronize digital audio signals. This provides basic requirements for processing remote program sources in the studio. For system engineering in this area, the development of actual work should follow Standardization of sampling frequency and international consensus on serial transmission formats in the professional field. In 1984, the AES Standards Committee Digital Audio Association established a working group to consider policy options for the benefit of the industry. Performance issues. The approach is to get more than 60 equipment manufacturers to provide their suggestions and opinions. Society of Film and Television Engineers (SMPTE), the European Broadcasting Union (EBU), and the International Electrotechnical Commission (IEC ) engineers provided their opinions. final conclusion The AES3 and AES5 standards are recognized, and the principles applicable to synchronous operation are initially proposed, and then the future development of digital audio systems is considered. With the.1991 revision, more attention was paid to the use of AES3 signals when combining audio with digital video. In.1993, AES was A proposal was published in the Journal of the Sound Engineering Society (Vol. 41, No. 5). In October.1994, a working group and related SMPTE group convened a proposal. Joint meeting. Other meetings are held by representatives of SMPTE, IEC and EBU. This revision is the result of this recommendation and subsequent meetings. Digital audio system synchronization

1 Scope

This standard specifies two sets of parameters. The first group is about performance requirements for the successful exchange of digital audio data between devices; the second group is about Performance requirements for clock recovery in digital/analog and analog/digital conversion. This standard applies to the digital interconnection of digital audio equipment in a studio environment. It also applies to external connections to equipment in a studio environment. Signal source and 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. GB/T 14919-1994 Technical Specification for Digital Audio Signal Source Coding GY/T 158-2000 studio digital audio signal interface

3 terms and definitions

The following terms and definitions apply to this standard. 3.1 Synchronization Two digital audio signals should have exactly the same frame frequency (ie. two signals have the same number of frame). To successfully connect two digital audio devices, it is also necessary to ensure that the time difference between each sample of the two signals is within the allowable range. Time difference After the allowable value, even if the frequencies are exactly the same, one of the signals should be readjusted for synchronization. Note. This definition does not include correction of block format data. 3.2 AES/EBU frame Two consecutive and associated sub-frame sequences, each sub-frame carries audio sample data for one channel and is transmitted within a sampling period. 3.3 Time reference point GY/T 158-2000 The start conversion of the X or Z preamble of the digital audio signal frame.

4 working mode

4.1 Digital audio equipment should have the ability to lock the internal sampling clock generator to a digital audio reference signal (DARS). build It is recommended to provide additional input interfaces for the use of DARS. 4.2 Equipment synchronization shall use one of the following three methods. a) Use digital audio reference signals. This method ensures that the sampling clock of all input/output devices is locked on this reference signal. This This method is usually used in the studio; b) The digital audio input signal uses an embedded programmable sampling clock to lock the input/output sampling clock. This method will increase Add timing errors in cascaded digital device connections; c) Using audio and video reference signals that can extract digital audio reference signals, lock the video and audio signals at the same sampling frequency on. 4.3 The position of the digital audio reference signal shall comply with GY/T 158-2000. 4.4 When connecting external signals to another synchronized audio studio or broadcasting center, one of two methods should be used. a) When the input signal and the digital audio reference signal have the same sampling frequency but different phases, the number specified in GY/T 158-2000 should be used. Word audio frame correction; b) Sampling frequency conversion is required when the input signal and the digital audio reference signal have different sampling frequencies. 4.5 In an environment where video and audio are combined, the digital audio reference signal source should be locked to the video source to obtain the precision given in Table 1. True relationship. Table 1 Audio-video synchronization TV or movie audio samples per frame kHz 24Hz animation 25Hz 625 PAL and SECAM 30Hz 525 NTSC 30/1.001Hz NTSC 32 4000/3 1280 3200/3 16016/15 48.2000 1920 1600 8008/5 44.1 3675/2 1764 1470 147147/100 4.5.1 For video systems where one image frame contains an integer number of AES/EBU frame periods, the AES/EBU audio signal can be synchronized to image. 4.5.2 For video systems where one image frame contains non-integer AES/EBU frames, the audio signal specified in GY/T 158-2000 cannot Lock in sync with the video, unless there is an indicator in the video reference signal. Without this indicator, the video and audio output of the device are locked and cannot be used. Can meet the phase requirements in 5.3.

5 Device synchronization operation recommendations

5.1 Digital Audio Reference Signal 5.1.1 The digital audio reference signal should have the format and electrical configuration of a two-channel digital audio interface, and use GY/T 158-2000 Given the same connector. However, in the basic structure of the digital audio interface format, only when the sync preamble is set, digital audio The signal is considered a digital audio reference signal. When using multiple sampling frequencies, or when the sampling frequency does not comply with GB/T 14919-1994 (CCIR 646 [4], IEC 899 [6]) 5.2 of this standard does not apply. 5.1.2 Digital audio reference signals can be divided into two levels. a) that the primary reference signal is a high-precision signal that synchronizes multiple studio complex systems or independent studios; b) The secondary reference signal is a means of synchronizing a single studio that is not technically and economically necessary to operate on the primary reference signal. There are signals of recognized accuracy. 5.1.3 The main purpose of the digital audio reference signal is studio synchronization. For its specific application, the fourth word of the channel status data is required. The states of bits 0 and 1 of a section are represented. 00. no reference signal (default value); 01. First-level accuracy; 10. secondary accuracy; 11. Reserved. 5.1.4 When the digital audio reference signal contains other data, making it unusable as a normal audio signal, it should be used as a non-audio The frequency signal is defined in the channel state. 5.2 Allowable error of equipment sampling frequency 5.2.1 The equipment sampling frequency tolerance is determined by the long-term frequency drift of the internal crystal oscillator in a free-running state. This standard gives The allowable error of the sampling frequency of two-stage equipment is defined as 5.1 and 2 in 5.1 of this standard. a) The primary reference signal should maintain frequency accuracy for a long period of time within ± 1ppm (parts per million). Designed to provide first-level parameters Signal testing equipment can only lock other primary reference signals; Note. Even if the specified accuracy is specified for a single device sampling clock, if it is free running, the independent device (or other similar independent Processes, such as movies or images, cannot be maintained. b) The allowable error of the normal free operating frequency of the equipment for the secondary reference signal shall be as specified in GB/T 14919-1994. Within ± 10ppm. Note. The frequency allowable error is necessary for the working environment of the device, so the reference signal should always be used as the recommended operating condition for the manufacturer. 5.2.2 The minimum capture range of a device crystal oscillator designed to lock external input signals is. a) Level 1 equipment is ± 2ppm; b) ± 50 ppm for secondary equipment or other low performance instruments. 5.3 Device timing relationship 5.3.1 The time base point is used to define the timing relationship between digital audio reference signals and digital audio input and output signals. When the device is static When both the dynamic and dynamic conditions meet the following two conditions, they are considered synchronous. a) At the interface of the device, the difference between the time base points of all output signals and the digital audio synchronization signal should be within the digital audio frame period. Within ± 5% b) The receiving equipment should be designed so that the number of delayed samples of the signal after passing through the equipment is constant, and all input signals are synchronized with digital audio The difference of the time base point of the signal should be within ± 25% or ± 90 ° of the digital audio frame period. Note. At the input and output of the device, if the delay exceeds the frame period specified in GY/T 158-2000, the delay or delay range should be indicated in frames. Where the delay is known, the device interface panel should indicate the delay value. 5.3.2 The input signal time relationship is fixed but does not meet 5.3.1, the receiver should receive random phase input and have sufficient delay to avoid No sampling offset. In this case, sampling compensation is required. Note. The sufficient hysteresis effect is defined by the allowable error tolerance of the time base jitter at the receiving end in GY/T 158-2000. 5.3.3 Table 2 gives the absolute value of the allowable error for the sampling frequency specified in GY/T 158-2000 in 5.3.1 a) and 5.3.1 b). Table 2 Digital audio synchronization. limited Sync window μs Professional sampling frequency kHz 1/fs ± 25% allowable change ± 5% lock 32 31.25 ± 7.8 ± 1.6 44.1 22.68 ± 5.7 ± 1.1 48 20.83 ± 5.2 ± 1.0 5.3.4 In a system where the digital audio reference signal may originate from a video reference signal, the X or Z synchronization code of the digital audio reference signal At the beginning, at the beginning of the half-width point of the synchronization pulse of the first line of the television signal on each image frame that should conform to 4.5.1 of this standard (see figure 1). Half point of the first line of the sync pulse in the television frame Video sync signal Start time of sync code X or Z Digital audio reference signal Figure 1 Time correspondence between digital audio reference signals and video synchronization signals For image frames conforming to 4.5.2 of this standard, this correction will occur at every nth frame (NTSC. n = 5), and this frame is passed Video reference signal to identify. In this case, ± 1 sampling compensation can be performed, and care should be taken to provide sufficient lag Avoid random sampling offsets. For the situation in 5.3.4, except for the tolerance of ± 5% of the digital audio synchronization at the output of the system as defined in 5.3.1 a), There is an additional allowable tolerance of ± 5% between the video reference signal and the digital audio reference signal (see Figure 2). 5.4 System implementation A good system requires minimal timing errors between signal channels to avoid timing error accumulation and cause system synchronization. The synchronization signal defined in 5.4.1 3.1 allows the timing error to be less than 25% of the digital audio frame period. But hope the system synchronization can be the closest Performed at a critical point to minimize the impact of timing errors. 5.4.2 Timing error as shown in picture 2. 5% digital audio signal output 5% digital audio reference signal -5% digital audio reference signal -5% digital audio signal output Figure 2 Timing error 5.4.2.1 Delay effect Delay effects include the inherent delay of the device, the residual error of the phase-locked loop, and the cable delay in the transmission path. Caused by these factors The delay varies with the audio system equipment configuration. 5.4.2.2 Time base jitter The time base jitter noise can be random or modulated. When the frequency is less than the sampling frequency, it will cause timing errors according to the amplitude of the modulation wave. Degree and frequency accumulation. Note. GY/T 158-2000 defines the limits of jitter at digital audio interfaces.

6 Audio sample clock requirements

In order to achieve the best digital/analog and analog/digital conversion performance, when the digital audio reference signal is externally locked, The jitter and jitter modulation range has higher timing accuracy than first-order signals. 25% 10% 5% -25% -10% -5% Video reference

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