hdf-0.11: Help/UGen/Filter/lag.help.lhs
> import Sound.DF
> do { s <- sin_osc 0.05 0.0
> ; let f = lin_lin s (-1.0) 1.0 220.0 440.0
> in do { o <- sin_osc f 0.0
> ; f' <- lag f 1.0
> ; o' <- sin_osc f' 0.0
> ; audition [] (out2 (o * 0.2, o' * 0.2)) } }