GY/T 193-2003Synchronization of digital audio system (English PDF)

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

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.