transpose just the midi

[Neuro]

Excuse me,  one small questions.
How can I transpose just the midi output?

for example, French horn is in F; we want it sounds fifth lower than 
written.

Here are the examples,

0  %% file horn.ly
1 horn = {
2 \set Staff.instrumentName = \markup { \column { "Horn " \line { "in 
F" } } }
3 \set Staff.midiInstrument = "french horn"
4 \clef treble
5 \key c \major
6 \time 4/4
7 c' 1 \ppp
8 \bar "|."
9 }

00 %% file music.ly
01 \version "2.10.5"
02 \include "horn.ly"
03 \header { }
04 \score {
05 \horn
06 \layout { }
07 \midi{
08  \context {
09   \Voice
10   \remove "Dynamic_performer"
11   \remove "Span_dynamic_performer"
12   }
13  }
14 }

# so we can run
# lilypond music.ly

Now, the printed music is good, but the midi is not "in tune."
It's in "concert" pitch C, but I want it written pitch C as in F horn, that 
is concert pitch "F."


... sure we can transpose the horn (for example to the fwllowing file), make 
a whoe set of scores, re-run the lilypond for the midi.

0 %% file horn.ly
1 horn = \transpose f c {
2 \set Staff.instrumentName = \markup { \column { "Horn " \line { "in 
F" } } }
3 \set Staff.midiInstrument = "french horn"
4 \clef treble
5 \key c \major
6 \time 4/4
7 c' 1 \ppp
8 \bar "|."
9 }


00 %% file music_for_horn_in_F_midi.ly
01 \version "2.10.5"
02 \include "horn_for_midi.ly"
03 \header {}
04 \score {
05 \horn
06 \layout { }
07 \midi{
08  \context {
09   \Voice
10   \remove "Dynamic_performer"
11  \remove "Span_dynamic_performer"
12  }
13  }
14 }

# so we can run
# lilypond music_for_horn_in_F_midi.ly


But, is there a simler way? perhaps like ...

\midi {
   \transpose f c \horn
}

%% or

\midi {
\context {
   \transpose f c \horn
}
}

%% or

\midi {
\context {
 \voice {
   \transpose f c \horn
 }
}
}



Thank you very much.
and
Nappy New Year


Neuro