Kick 2 by Sonic Academy is my fav for kick drums
Great scope built in, can tune to a fundamental frequency, can add clicks to the attack portion of the kick, distort, compress, eq etc etc
Really powerful stuff
Kicks are generally always just pitch modulated sine waves
And the click in the beginning generally is wether the wavecycle starts at a zero-crossing or not and how the rest of the sound is being filtered.
But to be honest, I don’t really like diy kicks on the Digitakt, there’s something that makes them sound a bit too modern and mid-heavy. The Volca Sample was really good at doing oomphy kicks, sometimes I miss the box.