The decibel (dB) is a logarithmic unit used to measure the intensity of a sound or the level of an electrical signal.

Instead of being a linear unit (like meters or kilograms), the decibel expresses a ratio between two quantities. It is used in audio because our hearing also works logarithmically, not linearly.

Think of the Richter Scale for earthquakes: a magnitude 7 earthquake is not a little stronger than a magnitude 6 earthquake; it is ten times stronger. The decibel works in a similar way. A change of a few dB represents a large change in sound intensity.

Because it is a relative unit, the decibel needs a suffix to indicate the reference point. For example:

• dB SPL: Measures the sound pressure in the air (the "volume" we hear).

• dBFS: Measures the level in a digital system, where 0 dBFS is the maximum possible.

• dBu / dBV: Measure the voltage in an analog system.