Decibels in audio

Sound pressure is the change in local atmospheric pressure caused by sound waves. This value is measured in Pascals (1 Pascal = 1 Pa = 1 Newton per square meter). Humans can hear sound at roughly 0.000002 Pa = $2 \times 10^{-5}$ Pa = 20 μPa. (This is equivalent to the sound of a mosquito flying 3 meters away.) Sound at 20 Pa is when it starts to become physically painful to hear.¹²

In short, the range of a human's hearing is $2 \times 10^{-5}$ Pa to 20 Pa.

For the sake of convenience, we define 0 dB SPL = $2 \times 10^{-5}$ Pa. dB SPL is logarithmic:

Pa	dB SPL
0.00002	0
0.0002	20
0.002	40
0.02	60
0.2	80
2	100
20	120

To calculate dB SPL from sound pressure: $L_p = 20 \log_{10}{\frac{p}{p_0}} \text{dB}$

where $p_0 = 20 \text{μPa}$.