What is dB (decibel) in audio?

When you adjust the volume on your audio interface, loudspeaker, or even your phone, you are changing the sound pressure level the device will produce, represented best as an increase or decrease on the decibel scale.

And when you see a specification for the sensitivity of a microphone or loudspeaker, it is often expressed in dB.

The main function of the dB is to compare values via a ratio between one value and a reference value.

In the case of SPL (Sound Pressure Level), the reference value (0 dB) is the threshold of human hearing. Interestingly, the relationship between the intensity of sound and light and human perception is better represented by the logarithm of intensity, rather than a linear relationship. 

So, be aware that the dB scale is logarithmic as a seemingly small change in dB can represent a significant change in the actual sound level.

A change of just +6 dB gives you double the signal strength, +20 dB leads to 10 times the signal, + 40 dB leads to 100 times the signal*.

*valid for dBSPL, dBV, and dBU

As mentioned: The most important thing about the decibel scale is that we can use it to compare one value to a reference value.

After a while, you'll quickly get a feel for how the dB values translate to practical things when recording or mixing. This will also help you to better understand technical data and make devices, and signal flows more comparable.