SDI, HD-SDI, 3G-SDI, 6G-SDI, 12G-SDI: What are the ...
SDI, HD-SDI, 3G-SDI, 6G-SDI, 12G-SDI: What are the Differences?
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As broadcast, live events, and various high-bandwidth applications continue to demand more, the SDI standard has undergone continuous evolution. SDI (Serial Digital Interface) is extensively used in SDI encoders, SDI converters, and other equipment, finding applications in radio, television, and security monitoring. But what exactly are HD-SDI, 3G-SDI, 6G-SDI, and 12G-SDI, and how do they differ?
What is SDI?
The SMPTE group developed the SDI (Serial Digital Interface) standard for digital video. This interface sends all bits of the data word and related data through a single channel. Due to the high data rate, serial digital signals must be managed before transmission.
SDI is a digital video transmission technology widely used in broadcasting, live events, and professional settings. It uses two coaxial cords to send one digital signal via optical fiber at speeds ranging from 270 Mbps to 12 Gbps. As a point-to-point interface, each wire transports data from one device to another.
What is HD-SDI?
HD-SDI (High-Definition Serial Digital Interface) is standardized in SMPTE 292M. Although often referred to as the 1.5 Gb/s interface, the supported bit rates are 1.485 Gb/s and 1.485/1.001 Gb/s. 3G-SDI optical transceiver offers a diverse range of HD-SDI transceivers designed for special broadcast applications.
What is 3G-SDI?
3G-SDI standardizes a bit-serial data structure, electrical signal, and coaxial cable interface for transporting signals with total payloads of 5.940 Gb/s or 5.940/1.001 Gb/s. This standard also outlines the electrical and physical characteristics of coaxial cables and connectors. It defines various mapping modes for delivering 2160-line and 1080-line image formats and associated ancillary data into a Single-link 6 Gb/s SDI bit-serial interface.
What is 6G-SDI?
The SD SDI standard supports a 270 Mb/s data rate. It uses a 27 MHz clock rate to deliver low-resolution PAL video at 25 frames per second. Established by the ITU-R in 1994, it features non-Zero Reverse (NRZI) encoding and 10-bit transmission, mainly used for 480i and 576i video formats.
What is 12G-SDI?
12G-SDI is a high-resolution, enhanced frame-rate SDI standard with a commitment to high-color quality. With four times the capacity of HD, it can transmit at 12 Gbps, making it ideal for 4K 60p video formats at 60 FPS.
Comparing SD-SDI vs. HD-SDI
Although HD-SDI and SD-SDI share similar basic electrical specifications, the transmission bit rate of HD-SDI is significantly higher. ITU-R BT.1120-2 specifies the luminance sampling frequency of high-definition video signals as 74.25 MHz and the chrominance sampling frequency as 37.125 MHz, resulting in an HD-SDI bit rate of 1.485 Gb/s. High-frequency transmission cable parameters influence the distance over which high-definition video signals can be transmitted, reducing the cable length significantly.
The data transmission format of HD-SDI is similar to that of SD-SDI. Time-division multiplexing handles the luminance signal Y and chrominance signals Cb and Cr as 20-bit words, each corresponding to a color difference sample and a luminance sample. The multiplexing modes are: (Cb1Y1), (Cr1Y2), (Cb3Y3), (Cr3, Y4).
3G-SDI, 6G-SDI, 12G-SDI: What are the Differences?
Here is a brief comparison table of various SDI:
Advantages of Optical Fiber Cable in Audio and Video Transmission
1. Long-Distance Transmission
If the video transmission distance exceeds 100 meters, copper cables require repeaters or additional network equipment, increasing project costs and potential future issues. Optical fiber can easily solve this problem with CWDM and DWDM uncompressed technology for audio and video extension without compression or transmission delay.
2. Electromagnetic Interference
In environments with numerous electromagnetic interference sources (e.g., factories, hospitals, air conditioning rooms, power rooms), optical fiber cables operate stably without electromagnetic interference. This is because they are made of glass, not metal.
3. Confidentiality
Optical fibers do not emit electromagnetic radiation, making it extremely difficult to detect transmitted signals. This is beneficial in high-security environments such as military, R&D, auditing, and government sectors.
4. High Bandwidth
Optical fiber is ideal for environments demanding high bandwidths, exceeding 1G. Fiber optic cables offer virtually unlimited bandwidth. Currently, 100G fiber optic modules are available on the market.
In recent years, single-mode fiber optic cables have become widely used in AV transmission projects, as they offer similar costs to multimode fiber cables but can transmit signals over longer distances. For digital video formats like SDI, HDMI, and DVI, single-mode fiber extenders can transmit up to 120KM, while multimode maxes out at 2KM. Increasingly, SFP module suppliers use single-mode SFP modules for these applications, but multimode solutions still face distance limitations of up to 300 meters. There is no CWDM or DWDM solution for multimode cables in video transmission.
For example, a 16-channel 3G-SDI fiber optic extender can transmit SDI video over one multimode optical cable. However, this setup may lack stability since it utilizes single-mode type SFP modules and MUX/DMUX internally.
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