hdf-0.11: Help/UGen/Oscillator/impulse.help.lhs
> import Sound.DF
> do { o <- impulse 800.0 0.0
> ; audition [] (out1 (o * 0.1)) }
> do { f <- fmap (\x -> x * 2500.0 + 2505.0) (sin_osc 0.25 0.0)
> ; o <- impulse f 0.0
> ; audition [] (out1 (o * 0.1)) }