bandf :: Pattern Double -> ControlPattern
bandf turns a number pattern into a control pattern that sets the center frequency of a band pass filter. In SuperDirt, this is in Hz (try a range between 0 and 10000). In classic dirt, it is from 0 to 1.
You can use bpf as a shortcut for bandf.
d1 $ s "drum*8" # bandf "100 1000 2000"