In audio cables, XLR cables are mainly used for connecting microphones. With the development of USB connected microphones, why is XLR cable still in demand? This article will further analyze XLR cables in detail.
一, Connection between XLR cable and microphone
Most professional independent microphones, whether they are dynamic microphones, condenser microphones, or ribbon microphones, have XLR output. Similarly, the vast majority of microphone inputs (whether in a mixing console, audio interface, adapter, or standalone microphone preamplifier or processor) have XLR inputs. These microphone inputs are actually 3-pin female XLR connectors.
Looking at the standard 3-pin XLR cable, we will see two connection points: one end has a 3-pin XLR male connector, and the other end has a 3-pin XLR female connector.
1. The male end of the 3-pin XLR connector has 3 pins, which are used as plugs. When connecting, insert the 3-pin XLR male head into the 3-pin XLR female head.
2. The three pins of the 3-pin XLR female connector serve as sockets, which can accommodate 3-pin XLR male connectors when connected.
Therefore, we have three devices for basic microphone connection through XLR:
1. The microphone itself (a professional microphone with XLR output connector).
2. 3-pin XLR cable (also known as "microphone cable").
3. Microphone input (assuming we connect the microphone to the audio interface in this example).
二, Analysis of the Pin Function of XLR Cable
Pin 1: Pin 1 is the ground/shield wire. It provides reference points for pins 2 and 3, and can also be connected to ground at the microphone and/or microphone input. Most importantly, pin 1 also serves as a cable shielding layer, protecting pins 2 and 3 from electromagnetic interference.
Pin 2: Pin 2 is the live/positive wire. It carries a copy of the positive polarity audio signal. In the case of microphone connection, it transmits the positive microphone signal from the microphone to the connected microphone input.
Pin 3: Pin 3 is the cold/negative wire. It carries a copy of the audio signal with negative (opposite) polarity. In the case of microphone connection, it transmits negative microphone signals from the microphone to the connected microphone input.
Therefore, the microphone outputs audio signals with equal amplitude but opposite polarity on pins 2 and 3 (relative to pin 1).
These twin audio signals are transmitted through balanced XLR cables and sent to the next audio device. Any audio interface's microphone input may have a built-in microphone preamplifier. In the microphone preamplifier that requires microphone level balancing of audio signals, there is a differential amplifier.
The differential amplifier adds the difference between the audio signals on pins 2 and 3 of the balanced XLR cable. This effectively doubles the amplitude of the microphone signal while eliminating any similarities between pins 2 and 3. This is called common mode rejection.
