Understand dB

For example,

gain response could be specified as 0.707 or as −3.0103 dB,

gain might be specified as 0.0001 or −80.0 dB.

Formula --

gain dB = 20⋅ log(gain)

Reason :

values in decibels are more manageable for very small
gains



reference :

1: Practical Analog and Digital Filter Design (Artech House Microwave Library) by Les Thede