If you listen to metal music you may wonder how things that are not bass guitars sound so bassy. The answer (on top of the use of drop D tuning, sometimes up to three semitones down) is that some amps and some effects pedals allow you to generate and blend in a note that is an octave below the note(s) being fingered. That is an octave divider, sometimes called octivider.

The sound hits you. That's grunt.