At any point in a
transmission system
:''See Transmission (mechanics) for a car's transmission system''
In telecommunications, a transmission system is a system that transmits a signal from one place to another. The signal can be an Signal (electrical engineering), electrical, optical ...
, the ratio of the
circuit noise
Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference arise ...
at that point to an arbitrary level chosen as a reference.
The circuit
noise level is usually expressed in dBrn0, signifying the reading of a circuit noise meter, or in
dBa0, signifying circuit noise meter reading adjusted to represent an interfering effect under specified conditions.
{{telecomm-stub
Noise (electronics)