The Knowledge of Audio Cable

- Oct 10, 2018-

According to the characteristics of audio signals, it can be divided into analog audio signals and digital audio signals. Whether it is the interconnection between audio devices or the connection between music production equipment and sound playback equipment, a medium is needed—the audio cable, which is responsible for the transmission of audio data. Audio cables can be divided into analog audio cables and digital audio cables depending on the characteristics of the transmitted audio signal.

First, the analog audio cable

Analog audio cables can be divided into microphone audio cables, transmission line cables, and speaker cables. Usually, the central part of the audio cable is a conductor, which serves as a carrier for the audio signal; the outer layer of the conductor is wrapped with a non-conductive plastic or rubber; and the outer layer is a shield composed of a conductor, which isolates the external interference on the one hand, On the one hand, the ground loop that constitutes the signal; the outermost layer protects the inner layers and makes the cable durable. Analog audio cables generally use copper wires as conductors because they are low in cost, good in electrical conductivity, and relatively flexible. However, when copper conductors are exposed to the air, they are easily oxidized and become poor conductors of copper oxide, which affects the conduction of current. Analog audio cables often use a variety of plug-in types such as XLR, 1/4 inch or RCA port.

Two metal objects with an insulator in the analog audio cable can form a capacitor. The shield and inner conductor of the audio cable are exactly such a relationship, so the entire cable forms a large capacitance, and its capacitive reactance blocks the flow of alternating current. . According to the nature of the capacitor, the frequency rise will reduce the capacitive reactance, and the capacitance will be combined with the resistance of the cable to form a low-pass filter. The longer the cable cuts, the lower the cutoff frequency point, and the greater the attenuation, which is usually not recommended. Another property of the wire is the inductive reactance, which produces a magnetic field that varies with voltage as it circulates through the wire, known in physics as "self-inductance." This magnetic field produces a resistance to the passage of the signal, which becomes smaller as the frequency decreases, and interaction with resistance and capacitive reactance produces complex results.

Second, digital audio cable

Digital audio cable for solid core copper conductor coaxial cable for transmission of AES/EBU digital audio signals and single-pair shielded twisted pair cable, commonly used for professional digital audio interface and S/PDIF for balanced transmission of AES/EBU XLR Digital audio interface. Its characteristic parameters: sampling rate is 32kHz-192kHz; bandwidth is 4.069MHz-24.5MHz; rate is 3.072Mb/s. Digital audio cable specifications: Audio coaxial cable with RG11, RG6, RG59, miniRG59 and RG179; audio twisted pair cable with 22AWG, 24 AWG and 26 AWG.

The advantage of the twisted-pair shielded cable is that it is easier to lay down when the transmission distance is short. Compared with other transmission methods, the investment is relatively small, the technology is mature, and the maintenance is convenient; the disadvantage is that the frequency response is poor when the transmission distance is long. AES/EBU specifies the transmission standard for digital audio signals up to 100 m in length, and the signal source and load impedance should be 110 Ω. Because the frequency of the AES/EBU digital audio signal is as high as 6 MHz, the capacitance and high frequency loss will cause high frequency drops, and the edge of the final audio signal will be rounded and the amplitude will be reduced, so that the receiver cannot recognize "1" and "0", so use 110Ω balanced transmission within 100m. If you use a transmission cable of 100m or more, you can select an equalizer on the cable terminal receiver to improve transmission efficiency. You can also use an unbalanced coaxial audio cable with 75Ω impedance.



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