By changing (dampening) the rate of vibration. Sometimes when I get sloppy or tired I will get the tongue thru the teeth on occasion and I can hear the slightest flattening of the tone. My goal is to have the notes sound like a bell rung with a mallet, same tone with only slight interruption. Kind of like when Greg does the tube and balloon thing and the same sound just stops and starts. Its a very small thing in the big picture, just one I work on. If you’ve heard someone play whos having trouble with attack and you hear a Twaa Twaa sound instead of the Taa Taa, just trying to be sure I taa taa.