External voltage distance
The external voltage distance is the ratio of useful voltage to external voltage of a transmission system for acoustic signals. The external voltage is a noise level caused by system-related sources of interference in the transmission system.
To determine the external voltage distance, the external voltage is related to the useful voltage ( useful electrical signal ) of the transmission system in accordance with the following relationship , logarithmized and specified in d B :
- U n is the useful voltage
- U f is the external voltage.
The noise voltage measured with the weighting filter is called the noise voltage .