What are the white bars at the bottom of notes for?

[MelodyBeat]

Image of what I'm talking about:

 See the little bar that's about half-full at the bottom of the note?

At first I thought the bars represented the instrument's volume, but that doesn't seem to be it, because I have seen instruments with their volume turned all the way up that still have these little bars at the bottom of the notes. What do they mean?

[LucentTear]

it's just individual note volume, you can use alt+scroll wheel or alt+/- to adjust it on selected notes

[tbyunomi]

Yes, or you could refer to it as velocity

[Lopyt]

Actually its an indicator to what notes are under section 12A of American Copyright Legislation

[MelodyBeat]

it's just individual note volume, you can use alt+scroll wheel or alt+/- to adjust it on selected notes

Oh wow, I had no idea you could do that! Thank you for explaining!