It can transmit LPCM streams and surround sound compressed audio signals, such as dolby digital and DTS. SPDIF can be divided into coaxial and optical fiber from the transmission medium. In fact, the signals they can transmit are the same, but the carriers are different, and the interface and connection appearance are also different. Optical signal transmission is a popular trend in the future, and its main advantages are flexible interface and stronger anti-interference ability, regardless of interface level and impedance.

Coaxial SPDIF is generally called coaxial input, which is marked with coaxial on the equipment backplane. Digital coaxial interface adopts coaxial cable with impedance of 75 Ω as transmission medium, which has the advantages of constant impedance, wide transmission frequency band and high-quality coaxial cable bandwidth up to several hundred megahertz. The time base error of digital coaxial transmission is very small, so this transmission mode has a good performance in sound quality.

But when using, please pay attention to the impedance matching of transmission line, and cooperate with 75 Ω coaxial cable to ensure constant impedance and correct signal transmission. That is to say, in the matching of transmission lines, 75 ohm coaxial line suitable for transmitting high-frequency digital signals should be used as the matching standard, which is commonly called "digital line".

Generally speaking, the audio quality of coaxial terminal output and optical fiber output is similar. So some DVD players only set digital coaxial output, omitting the optical fiber output function.

Extended data

Coaxial audio interface connectors are divided into RCA and BNC. Coaxial audio is an audio interface with input and output functions. Different from the previous audio interface, it integrates the microphone interface (input interface) and the earphone or stereo interface (output interface). Digital Coaxial is an interface that uses S/PDIF interface to output digital audio.

Coaxial cable has two concentric conductors, which are coaxial with the shielding layer. Coaxial cable is a copper conductor separated by insulating material with an impedance of 75 ohms. Outside the inner insulating material is another layer of annular conductor and its insulator. The whole cable is wrapped by a sheath made of PVC or PTFE. The advantages of coaxial cable are stable impedance and high transmission bandwidth, which ensures the quality of audio.

Digital coaxial interface adopts coaxial cable with impedance of 75 Ω as transmission medium, which has the advantages of constant impedance, wide transmission frequency band and high-quality coaxial cable bandwidth up to several hundred megahertz. The standard connector of coaxial digital transmission line adopts BNC connector with an impedance of 75 Ω. When matched with 75 Ω coaxial cable, it can ensure constant impedance and correct signal transmission.

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