Common audio interface introduction (1): analog audio interface

When we use audio products, the first thing to face is connectivity. In addition to the power cord, everyone is familiar with it, and there are a lot of dense audio interfaces, which are often dazzling. These interfaces have different functions, but some interfaces have different functions, but the appearance is almost the same, which causes a lot of trouble to many users.

1. RCA interface

RCA interface is also very common in our daily life. Basically there are speakers, TVs and other equipment. Its name comes from the abbreviation of Radio Corporation of America, which introduced the interface to the market in the 1940s for connecting phonographs and speakers. The joint we are more familiar with is called “Liantou”.

The RCA interface adopts the coaxial transmission mode, the central axis transmits signals, and the outer ring of the contact layer is grounded. Each RCA cable is responsible for transmitting the audio signal of one channel, so the matching number of RCA cables can be used according to the actual needs of the channel. For example, two RCA cables are required to set up two-channel stereo.

2. XLR interface

The XLR interface is also called “Canon port”. Canon Electric Company is made by James H. The original manufacturer created by Canon. Their first product is the “Canon X” series. Later, the improved product added a latch, so an “L” was added after the “X”; later, a rubber compound was added around the metal contacts of the connector, so an additional one was added after the “L” “R”. People put the three capital letters together and call this connector “XLR connector”.

The XLR plug we usually see is 3 pins, of course, there are 2 pins, 4 pins, 5 pins, 6 pins. For example, in some high-end headphone cables, we will also see quad-core XLR balanced connectors. The XLR interface is the same as the “three major” TRS interfaces and can be used to transmit audio balanced signals. Of course, the XLR interface can transmit unbalanced signals like the “big three core” TRS interface, so we can’t see what kind of signal it transmits from the interface.

3. TRS interface

The TRS interface is one of the most used interfaces in our daily lives. Its shape is cylindrical, usually in three sizes: 1/4″; (6.3mm), 1/8″; (3.5mm), 3/32″; (2.5mm). Our most common size is 3.5 Mm.

The 2.5mm TRS interface used to be popular in mobile phone headsets, but it is now rare. The 3.5mm interface is basically unified. 6.3mm interface is more common in many professional equipment and high-end headphones, but now many high-end headphones are gradually changed to 3.5mm interface. TRS refers to tip (signal), ring (signal) and sleep (ground), and represents the three contacts of this type of connector. What we see is three metal pillars separated by two insulating materials. Therefore, 3.5mm connectors and 6.3mm connectors are also called “small three-core” and “large three-core”.

The TRS interface is a round hole, which has three contacts corresponding to the connector, and is separated from each other by an insulating material. There is also a four-pin plug. The extra core is used to transmit voice signals or control signals. Another 4-pin 3.5mm headphone plug is used to transmit balanced signals. The 6.3mm “big three-core” plug can transmit balanced signals or unbalanced stereo signals, but due to the high cost of making such balanced cables, it is generally only used for high-end professional audio equipment. Let us briefly talk about balanced and unbalanced signals. After the sound wave is converted into an electrical signal, if the direct transmission is an unbalanced signal, if the original signal is 180 degrees inverted, then the original signal and the inverted signal are transmitted at the same time, which is the balanced signal. Balanced transmission refers to the principle of phase cancellation during the transmission of audio signals to minimize other interference.

There is also a dual-core connector that can be used to transmit unbalanced mono audio signals. For example, the electric guitar cable is a twin-core TRS cable. Therefore, from the appearance of the TRS interface alone, we do not know whether it supports balanced transmission; from the core number alone, we cannot determine whether 4 or more TRS interfaces support balanced transmission, depending on the device.

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