# Controlling FX

It is also possible to control FX, although this is achieved in a slightly different way:

    with_fx :reverb do |r|
      play 50
      sleep 0.5
      control r, mix: 0.7
      play 55
      sleep 1
      control r, mix: 0.9
      sleep 1
      play 62
    end

Instead of using a variable, we use the goalpost parameters of the do/end block. Inside the `|` bars, we need to specify a unique name for our running FX which we then reference from the containing do/end block. This behaviour is identical to using parameterised functions.

Now go and control some synths and FX!