Velocity
Velocity is how hard a MIDI note was played. It is stored on the note. The channel fader is the loudness of the whole track.
Velocity is how hard a MIDI note was played, stored on the note. The channel fader is separate. It sets the loudness of the whole track.
What the number does depends on the instrument. Many synths use it to open the filter or raise the level, so a harder note is brighter as well as louder. A sampler may switch to a different recording. If a patch ignores velocity, the notes still keep the value for a patch that uses it. Accent on Beatbox 9 is the sequencer version: chosen steps are emphasized, and Accent Amount sets how loud the other steps are beside them.
In the MIDI editor, each note has a bar in the lane under the grid. Drag a bar to set that note. Hold Ctrl or Cmd and drag the note itself to change it from the grid. Select several notes and drag the lane to scale them together, so the differences between them stay. Repeated notes at one velocity sound mechanical. Alternating higher and lower values is enough to loosen a hat or a chord. Humanize can scatter them for you.