Ground lift
Encyclopedia
In sound recording and reproduction
, ground lift or earth lift is a technique used to reduce or eliminate ground
-related noise
when connecting signal lines between two or more pieces of equipment. It interrupts the ground line at some point. It is particularly effective at eliminating ground loops
, but it may also increase or decrease noise from other sources.
If all pieces of equipment are tied to a common ground reference, no current flows in the ground conductors and cable shields, and no noise is introduced into signal circuits. In applications such as sound reinforcement
for a concert, however, it is difficult to ensure all equipment shares a common ground reference.
s may have a ground lift switch for the cable shield. The ground lift switch eliminates unwanted hum and buzz by interrupting the ground loops
between equipment, preventing current flow along the cable shield between two devices. The switch disconnects pin 1 on the XLR
jack, which is connected to the braid or foil shield in the cable and acts as the ground point of the circuit.
Ground lifts do not conform to Audio Engineering Society
standard AES48.
) in a power lead in which the ground conductor is deliberately disconnected, or by cutting a ground pin in the power plug. If a fault develops in any line-operated equipment, cable shields and equipment enclosures may become energized, creating an electric shock hazard. For example, the metal shell of a stage microphone or the strings of a guitar may become energized, creating a hazard to performers. Wireless microphones and guitar pickups eliminate this hazard.
Sound recording and reproduction
Sound recording and reproduction is an electrical or mechanical inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects. The two main classes of sound recording technology are analog recording and digital recording...
, ground lift or earth lift is a technique used to reduce or eliminate ground
Ground (electricity)
In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....
-related noise
Noise (audio)
Noise in audio, recording, and broadcast systems refers to the residual low level sound that is heard in quiet periods of a programme....
when connecting signal lines between two or more pieces of equipment. It interrupts the ground line at some point. It is particularly effective at eliminating ground loops
Ground loop (electricity)
In an electrical system, a ground loop usually refers to a current, almost always unwanted, in a conductor connecting two points that are supposed to be at the same potential, often ground, but are actually at different potentials. Ground loops created by improperly designed or improperly installed...
, but it may also increase or decrease noise from other sources.
If all pieces of equipment are tied to a common ground reference, no current flows in the ground conductors and cable shields, and no noise is introduced into signal circuits. In applications such as sound reinforcement
Sound reinforcement system
A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience...
for a concert, however, it is difficult to ensure all equipment shares a common ground reference.
Ground lift switch
Professional audio equipment intended for use with balanced lineBalanced line
In telecommunications and professional audio, a balanced line or balanced signal pair is a transmission line consisting of two conductors of the same type, each of which have equal impedances along their lengths and equal impedances to ground and to other circuits. The chief advantage of the...
s may have a ground lift switch for the cable shield. The ground lift switch eliminates unwanted hum and buzz by interrupting the ground loops
Ground loop (electricity)
In an electrical system, a ground loop usually refers to a current, almost always unwanted, in a conductor connecting two points that are supposed to be at the same potential, often ground, but are actually at different potentials. Ground loops created by improperly designed or improperly installed...
between equipment, preventing current flow along the cable shield between two devices. The switch disconnects pin 1 on the XLR
XLR connector
The XLR connector is a style of electrical connector, primarily found on professional audio, video, and stage lighting equipment. The connectors are circular in design and have between 3 and 7 pins...
jack, which is connected to the braid or foil shield in the cable and acts as the ground point of the circuit.
Ground lifts do not conform to Audio Engineering Society
Audio Engineering Society
Established in 1948, the Audio Engineering Society draws its membership from amongst engineers, scientists, other individuals with an interest or involvement in the professional audio industry. The membership largely comprises engineers developing devices or products for audio, and persons working...
standard AES48.
Other ways of isolating the cable shield
Specially wired signal adaptors may leave the shield connection disconnected, or connected to safety ground through an RF bypass capacitor. Isolation transformers may be used to convert from balanced lines to single-ended inputs, and also to isolate the cable shield from the equipment safety ground.Safety
Removal of the safety ground connection on equipment can expose users to an increased danger of electric shock and may contradict wiring regulations. The safety ground is disconnected by an adaptor (cheater plugCheater plug
A cheater plug, AC ground lifter or three-prong/two-prong adapter is an adapter that allows a NEMA 5-15P grounding-type plug to connect to a NEMA 1-15R non-grounding receptacle . The use of such an adapter avoids the need to replace receptacles, but is potentially hazardous, if the grounding tab...
) in a power lead in which the ground conductor is deliberately disconnected, or by cutting a ground pin in the power plug. If a fault develops in any line-operated equipment, cable shields and equipment enclosures may become energized, creating an electric shock hazard. For example, the metal shell of a stage microphone or the strings of a guitar may become energized, creating a hazard to performers. Wireless microphones and guitar pickups eliminate this hazard.