xexeo Yes 0db is the standard digital max volume. It means if a sound file is "normalised" the maximum peaks in the wave will be at 0db.
It avoids clipping where the tops of the waves get cut off causing distortion (you can't exceed 1111111111111111 in a 16bit file, which is your 0dB).
If your files are too quiet, you can "normalise" them using an audio editor, which will place the loudest sound in the sample at 0db.
Anything you want quieter should be reduced below that.
Audio editors allow you to go higher but its basically a multiplication (adding 6db for every perceived doubling in volume). With an audio editor you make sure you don't go into the red (which is the total audio output exceeding 0 db). So you could have a recording at -12dB and set +10dB in the audio editor, but your output would be -2dB. An audio editor will let you go into the red but the sound will be distorted.