This standard specifies the technical requirements and format of subcarrier transmission of four-channel digital sound signals. This standard is applicable to the transmission of four-channel high-quality mono or two-channel stereo programs by subcarrier while transmitting color TV programs on medium- and short-distance microwave relay lines or satellite broadcast relay lines. GB/T 14920-1994 Technical Specification for Four-channel Digital Sound Subcarrier System GB/T14920-1994 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
GB/T14920—1994
Technical Specification of the four channels digital sound sub-carrier system
Promulgated on January 26, 1994
State Administration of Technical Supervision
Implementation on September 1, 1994
National Standard of the People's Republic of China
Technical Specification of the four channels digital sound sub-carrier system
Specification of the four channels digital sound sub-carrier system
1 Subject content and scope of application
This standard specifies the technical requirements and format of subcarrier transmission of four-channel digital sound signals. GB/T14920—1994
This standard applies to the transmission of four-channel high-quality mono or two-channel stereo programs using subcarriers while transmitting color TV programs on medium-distance and short-distance microwave relay lines or satellite broadcast relay lines. 2 Reference standards
GB3174
Color TV broadcasting
Transmission characteristics and measurement methods of mono and stereo programs GB5438
3 Symbols and codes
"Exclusive OR" logic.
Delay 1 bit.
, most significant bit.
least significant bit.
System parameters
See Table 1 for the system parameters of digital sound subcarriers. Table 1
Sound signal bandwidth
Sampling frequency
Sampling time
Quantization and compression
Sound pre-emphasis
Approved by the State Administration of Technical Supervision on January 26, 1994 40Hz~15kHz
For stereo, the left and right channels are sampled simultaneously
14/10bit quasi-instantaneous compression and expansion (5 ranges)
See Appendix A (Supplement)
Implemented on September 1, 1994
Multiplexing
Bit rate
Number of sound channels
Additional data capacity
Number of bits in a frame
Bit allocation
Frame synchronization word|| tt||Control code
Bit interleaving
Spectrum randomization
Sound and data
Error correction
Range code
Control code
Subcarrier frequency
Main carrier frequency deviation caused by subcarrier
Subcarrier modulation method
GB/T14920—1994
Continued Table 1
2.048Mbit/s
4-channel mono or 2-channel stereo
480kbit/s
2048bit
See Figure 4
16bit/frame
16bit/sequence
32 bit
10 times m sequence
BCH-SEC-DED (63,56
BCH-SEC-DED (63,56) plus BCH-SEC-DED (7,3) majority decision
7.093790MHz±20Hz
±1.4~±4.0MHz
4-phase differential phase shift keying (4pDPSK)
Note: The subcarrier frequency values ​​listed in the table are based on the color subcarrier frequency of color television. 8/5 of the frequency, which is one of the subcarrier frequencies used in the digital sound subcarrier method.
5 Sound Coding Method
5.1 Sound Codeword Structure
Sound codewords are generated according to the 2's complement rule, as shown in Table 2. Table 2 Sound Codeword Structure
(Bit Number (Transmission Order)
Input Level
+FS-ILSB1)
Note: FS: Full Scale.
(MSB))
1) Positive Maximum Input Level.
2) Negative Maximum Input Level.
Determination of Range Code
The range code is defined by the maximum level of 32 consecutive sample values, as shown in Figure 1. The range code of this frame controls all sound sample values ​​in the next frame.
Input level
a14/10bit quasi-instantaneous compression (5 ranges) 6 frame structure
6.1 Bit interleaving and structure
GB/T14920—1994
Determination of range code
Range number
Range code
bRange code
Each frame consists of a matrix of 32 rows and 64 columns. The writing and transmission (reading) of the sending end bit starts from the first column of the first row, and the order is shown in Figure 2. The first 16 bits of the first column in a frame are used for frame synchronization, and the remaining 16 bits are used for control codes. The second to 57th columns of the matrix are allocated to voice and data bits. The 58th to 64th columns of the matrix are allocated to error correction bits. ?, .f
, the efficiency is
Figure 2 Bit interleaving matrix
6.2 Frame synchronization word
Frame synchronization word is generated by m sequence pseudo random code generator, as shown in Figure 3. When the initial value of the shift register in the generator is 1111, the 16 bits of its continuous output are taken out as the frame synchronization code. The code type of the frame synchronization code is as follows: 0001001101011110 (from left to right)3
7 Signal multiplexing
GB/T14920—1994
Generation formula = + + 1
Frame synchronization signal generation circuit
The conversion of mono, stereo or other modes in the signal multiplexing mode is realized by transmitting a 16-bit control code. 7.1 Multiplexed frame structure
1 The bit allocation of a frame is shown in Figure 4. The allocation of each bit in the bit interleaving matrix is ​​shown in Figure 5. In stereo broadcasting, the allocation of left and right channels is shown in Table 3.
2048it.s)
Channel 1
Control code
Channel 2
10 × 32
Channel +
10 x 82
Figure 4 Bit allocation of signal multiplexing
To channel 3
By channel 2
Figure 5 Bit allocation on the multi-channel bit interleaving matrix Table 3 Application of stereo channels
Channel 2
First stereo channel (TV sound)
Left channel
Bit allocation of 7.2 control code
Right channel
Channel 3
Additional integer
* × x2 - 491
Second stereo
Left channel
Ma Renshun center
Channel 4
Right channel
The 16 bits of the control code are bits 17 to 32 of the first column in the bit interleaved matrix, and their allocation is shown in Table 4. 4
Bit number
Unassigned
7.3 Transmission format of range code
GB/T14920—1994
Table 4 Bit allocation of control code
00 First stereo channel (TV accompaniment sound)
Mono, only channel 1
2nd mono channel
Unassigned
00 Second stereo channel
Mono, only channel 3
012nd mono channel
11 Data transmission
The range code is transmitted using the second bit of each line. Its format is shown in Figure 6. Transmission sequence
Generation 1
Figure 6 Transmission format of range codebzxz.net
8 Error correction
8.1 Voice and data bits
For error correction of voice and data, BCH-SEC-DED (63,56) encoding is performed on the remaining 63 bits except the synchronization code and control code in each row of the bit interleaving matrix. At the transmitting end, the error correction code is generated by the circuit shown in Figure 7. Output
Generation formula = 27+2+22+1
Figure 7 BCH-SEC-DED (63,56) error correction code generation circuit 8.2 Range code
As the error correction method of range code, in addition to the error correction code described in the previous item, the BCH-SEC-DED (7,3) encoding method is also used for the range code.
At the transmitting end, the error correction code is generated by the circuit shown in Figure 8. 5
8.3 Control code
GB/T14920—1994
Generation formula = +2+22+1
Figure 8 BCH-SEC-DED (7,3) Error correction code generation circuit The error correction of the control code is completed by repeatedly transmitting the control code used to control the multiplexing mode in each frame and performing majority judgment. 9 Spectrum randomization
In order to randomize the spectrum, a pseudo-random code for scrambling must be added before the sound data signal is sent to the subcarrier modulator. The pseudo-random code generation circuit is shown in Figure 9.
The pseudo-random code is added to all bits except the frame synchronization code. Before the first bit of each frame of control code is sent out, all the linear feedback shift registers are set to 1.
Generation formula = 10 + 3 + 1
Figure 9 Pseudo-random code generation circuit
10 Subcarrier modulation
10.1 Subcarrier phase change and input signal data For the input signal sequence XY.X, Y....X, Y., the relationship between the double-bit symbol (YX data and the phase change is shown in Table 5.
Input data (Y., X.)
Phase change, degree
10.2 Subcarrier filtering characteristics at the transmitting end
GB/T14920—1994
The spectrum at the transmitting end forms a 30% roll-off characteristic as shown in Figure 10. 2
H-chemical secretion
(MH)
Relative amplitude
727427
5 Call piece
8. 5±0.55 414 5
t.532 1.5632
7. 0937900, 512
Note: The 30% roll-off characteristic is determined by the following formula: nf
V0.5[1+cos (f-0.35),
f: normalized frequency.
Transmit filter characteristics
0
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