Decibel (dB)
The decibel scale (specifically dBFS) is unusual in that it is 0dB at the maximum peak level and negative infinity at silence. It is a logarithmic scale, which is closer to the way human hearing perceives sound levels. You'll notice from the above figure that there are no positive levels. Levels below the maximum are negative. Only values above the maximum are positive (not shown) and such values may cause clipping. When changing the volume, positive values increase the level and negative values decrease the level.
Levels shown in most visuals are dBFS and not dBSPL.
Use the equation below to convert a decibel level to a percentage level.