Logarithmic sound pressure p, in relation to the sound pressure p o
The reference sound pressure p O (pO = 20 μPa) is equal to the noise pressure of the human hearing threshold level at 1000 Hz in dB. The noise level can also be determined for certain frequency bands.
The noise level states how much noise is present at the respective location. It gets smaller as the distance from the source of the noise increases, therefore the measuring distance must always be stated along with the noise level (for humans: normally 1 m).
In practice, calculating the noise level of a deployed machine is problematic: cf. Noise measurement.