Among audio cables, XLR cables are mainly used to connect microphones. Today, there are already microphones that can be connected via USB. Why are XLR cables still in demand? This article will further analyze XLR cables in detail.
1. Connection between XLR cables and microphones
Most professional independent microphones (whether dynamic, condenser, or ribbon) have XLR outputs. Similarly, the vast majority of microphone inputs (whether in mixing consoles, audio interfaces, adapters, or independent microphone preamps or processors) have XLR inputs. These microphone inputs are actually 3-pin female XLR connectors.
XLR Pro Audio Cable, XLR Male/XLR Female
Looking at a standard 3-pin XLR cable, we see two connection points: a 3-pin XLR male connector on one end and a 3-pin XLR female connector on the other end.
1. The male end of the 3-pin XLR connector has 3 pins and is used as a plug. When connected, the 3-pin XLR male plugs into the 3-pin XLR female plug.
2. The 3 pins of the 3-pin XLR female connector act as a jack (socket) that accepts a 3-pin XLR male connector when connected.
So we have three devices for basic microphone connection via XLR:
1. The microphone itself (a professional microphone with an XLR output connector).
2. The 3-pin XLR cable (also called a “mic cable”).
3. The microphone input (assuming we are connecting the microphone to an audio interface in this example).
2. Analysis of the Pin Functions of XLR Cables • XLR Pro Audio Cable, XLR Male Right Angle/XLR Female
Pin 1: Pin 1 is the ground/shield wire. It provides a reference point for pins 2 and 3 and can also be connected to ground at the microphone and/or microphone input. Most importantly, pin 1 also acts as a cable shield, protecting pins 2 and 3 from electromagnetic interference. Pin 2: Pin 2 is the hot/positive wire. It carries a copy of the positive polarity audio signal. In the case of a microphone connection, it transfers 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 negative (reverse) polarity audio signal. In the case of a microphone connection, it transfers the negative microphone signal from the microphone to the connected microphone input. Therefore, the microphone outputs audio signals of equal amplitude but opposite polarity on pins 2 and 3 (relative to pin 1). • XLR 3-pin Solder Connector, Female
These twinned audio signals are carried over a balanced XLR cable and sent to the next audio device. The microphone input of any audio interface is likely to have a built-in microphone preamplifier. Inside the microphone preamplifier, which requires a microphone-level balanced audio signal, there is a differential amplifier. The differential amplifier sums 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 canceling out any similarities between pins 2 and 3. This is called common-mode rejection. Common-mode rejection (CMR) is an effective way to eliminate any electromagnetic interference (EMI) that the XLR cable is subject to along its length. Although pins 2 and 3 are well isolated, there is still a chance that EMI (RF, 60 Hz hum, etc.) can affect the microphone signal. CMR helps eliminate this interference and allows for extremely long cable runs without noticeable signal quality loss.
