What are Decibels or dB?

Decibels or dB

This is a relative power unit. At audio frequencies a change of one decibel (abbreviated dB) is just detectable as a change in loudness under ideal conditions.

For a given power ratio the decibel change is calculated as:

dB = 10 log P2/P1

If we used voltage or current ratios instead then our formula becomes:

dB = 20 log V2/V1