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