This is cool stuff 
I added a few synths for chiptune around v2.10 which people might also want to checkout
:chipbass (a kind of steppy triangle waveform)
:chiplead (pretty much a straight square/pulse wave)
:chipnoise (1 bit noise as you'd find on old consoles like the NES)
Another way to make chip bass drum sounds is to use :chipbass and slide the note down very quickly as described in this video Kick drum synthesis