The decibel is a logarithmic unit which is used in a number of scientific disciplines. Its use in acoustics arises from the fact that typical acoustic pressures can vary by a factor of one million or more. Expressing this great range in terms of a logarithmic scale (i.e., decibels) instead of a linear scale (i.e., Pascals) allows us to describe sound levels with more manageable numbers.

In acoustics, the decibel is most often used to compare sound pressure in air with a reference pressure. Decibels are also used to describe sound power and sound intensity, however the references for these quantities are different. Therefore, when discussing decibels, one must know what quantity is being measured and what the reference is to ensure that valid comparisons are being made.