Sound pressure is the deviation of pressure from the undisturbed background. In linear acoustics, it is small compared with the background pressure; a microphone measures a response to this varying pressure, rather than directly recording fluid displacement.
The logarithmic level of root-mean-square sound pressure relative to a reference, conventionally in air. A pressure ratio changes level by decibels. The factor twenty follows from the square dependence of acoustic intensity on pressure in a fixed medium, combined with the power-level convention .
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Sound pressure is a measure of the local pressure variation from the ambient atmospheric pressure caused by a sound wave. It is typically expressed in pascals (Pa) and is a key parameter in acoustic measurements. When a sound wave travels through a medium (such as air, water, or solid materials), it causes fluctuations in pressure, which are perceived as sound.