Problem on the dynamics of the midi output

[Paolo Prete]

Hello.

I can't find a way to have a single sequence of dynamics that affects both upper and lower piano staves in the MIDI output.

I tried the following snippet but I can't hear any variation of the dynamics in the midi file.

%%%%%%%%%%%%%%%%%%%%%%%%%%%

\score {

<<

   \new PianoStaff <<

      \new Staff="up" { c'4 c' r r }

      \new Dynamics { s4\fff s s\ppp s}

      \new Staff="down" { r4 r c' c' }

   >>

>>

\layout { }

\midi { }

}

%%%%%%%%%%%%%%%%%%%%%

In addition, I wonder if is there a way to obtain the same result without having to add a "Dynamics" separate context...

thanks