When working with noise control, your noise abatement measures will depend entirely on the spectral properties of the noise. High-frequency noise is much easier to cope with than low-frequency noise. However, improvements effective on high-frequency noise are generally not effective on excessive low-frequency noise. Therefore you will sometimes need to have more detailed information on the frequency contents of the sound or noise you’re measuring.

To determine what measures are appropriate, you must do what is called a frequency analysis. The signal to be measured is electronically separated into various frequency bands, for example octave bands, each of which covers a 2:1 range of frequencies. A frequency analysis yields a series of levels, one for each band. These are referred to as “band levels”, or for octave bands, “octave-band levels”.