5 Noise in Audio Systems

Basics

When there is more than one piece of equipment in your sound system connected to a common ground through different paths, like different outlets on the same circuit, you can get a ground loop. As current flows through the system, the ground loop creates a circuit for the current to flow from one unit's ground to a second unit and back to the first. This current then creates hum (noise or interference) when it flows through the audio signal ground. If you break the ground loop, the noise is eliminated.

You should know the following terms:

  • Direct Box (Hum Eliminator)
  • Earth Ground
  • Floating Ground
  • Ground Loop Hum
  • Hum
  • RCA Connectors (Phono Connectors)
  • Residual-
    • Current Device (RCD), 
    • Ground-Fault Circuit Interrupter (GFCI)
    • Residual-Current Circuit Breaker (RCCB), and 

A floating ground can help eliminate ground loops, which reduces the noise coupled to the system.  Isolated in this manner, systems can and do drift in potential and if the transformer is capable of supplying much power, they can be dangerous. This is particularly likely if the floated system is near high voltage power lines. To reduce the danger of electric shocks, the chassis of the instruments are usually connected separately to an earth ground.

Noise can also be caused by a cabling issue that allows noise from the building's AC power lines into your equipment, called ground loop hum. This is caused by a difference in electrical potential at grounding points. 

Troubleshooting Noise in Your System

The simple, inexpensive way to fix the ground hum is to plug the piece of equipment into a different outlet that is on a different circuit. Once you can identify which piece of equipment is causing the problem, this is the easiest fix. For example, if the keyboard on stage creates a hum when it is plugged in, get an extension cord or move the keyboard so that it is no longer on the same circuit. 

Floating grounds can cause problems with audio equipment using RCA connectors (also called phono connectors). With these common connectors, the signal pin connects before the ground, and two pieces of equipment can have a greater difference between their grounds than it takes to saturate the audio input. As a result, plugging or unplugging while powered up can result in very loud noises in speakers. If the ground voltage difference is small, it tends to only cause hum and clicks.

Add devices such as a direct box or hum eliminator to decrease noise. These devices are created to reduce ground hum.

Because floating grounds can be more dangerous, use a residual-current device (RCD), residual-current circuit breaker (RCCB) or ground fault circuit interrupter (GFCI).  These are electrical safety devices that quickly break an electrical circuit with leakage current to ground. It is to protect equipment and to reduce the risk of serious harm from an ongoing electric shock.

The articles and videos in the Resources section provide additional information for eliminating noise and hum in your AV system.

Here are additional resources you may find useful:

Complete the following task or self-assessment:

Investigate: do you have noises in your AV system? 

You may try to set up a test system in an isolated area where you replicate a hum if you have not experienced it. Reset any device configurations to remove the hum and practice effective system management. Read the articles and watch the videos above and apply them to the problems in your system.