@yjmbo: yep, that's the beauty of it -- anyone can use whatever soundfont they'd like!
so up until the latest alda release, the only MIDI percussion instruments available in alda were the "percussive" set, general MIDI patches 113-120
each of these patches is just like any other MIDI patch -- the higher notes you use, the higher/lower the sample is played
but there is also a dedicated MIDI percussion channel, on which you can use these instruments: https://en.wikipedia.org/wiki/General_MIDI#Percussion
these work differently than the patches you can use on all the other MIDI channels
each note is mapped to a different drum/percussion sound
and you can't change the pitch