[...snip...]

In the Decibel scale, a 3 dB reduction equates to a reduction by 1/2. dB
scale is logarithmic. Depending upon whether one is converting from power
or not, the conversion from linear scale to logarithmic scale is either
dB = 10 * log10(P) or dB = 20 * log10(A).

But in human perception terms, according to audio textbooks I have, a
3 db increase is generally perceived as just noticeable, and a 10 db
increase is perceived as twice as loud.

Jim