A sound level meter is the instrument normally used to measure noise levels on the decibel scale. Several factors affect the noise level reading:
- The distance between the meter and the source of the sound
- The direction the noise source is facing, relative to the meter
- Whether the measurement is taken outdoors (where noise can dissipate) or indoors (where noise can reverberate)
For a reported sound level value to be most useful, it is necessary to specify the conditions under which the reading was taken, especially the distance from the source. Acoustic measurements in relation to noise are usually only measured vertically, and not horizontally.