Flexible Transposing a whole score

This code shows how to transpose a whole score by changing one single piece of code.

In the code the Scheme function MyTranspose is defined. If you use it in every Voice, you can transpose the whole score just by setting the arguments to the \transpose call within the function definition. As you see in the example this works with transposed voices as well (in the example I've written the Bb-Trumpet pitches as they sound, so they have to be additionaly transposed by \transpose bes c' {...}).

To see the original pitches, you may disable the MyTranspose function by redefining MyTranspose = {}, as shown in the lower part of the snippet.

\version "2.24.0"

%% http://lsr.di.unimi.it/LSR/Item?id=787

%here starts the snippet:

global = {
  \time 4/4
}

MyTranspose = 
#(define-music-function (m)
  (ly:music?)
  #{ \transpose f d $m #})
% In the previous line the transposition of the whole score is defined
% (in this case from f major down to d major).
\markup "Transposed from F to D"

% To deactivate the transposition remove the comment sign from the
% following line:
%MyTranspose = {}

Basekey = {
  \key f \major
}

FltPitches = \relative c'' { c d bes c }
TrpPitches = \relative c'' { c d bes c }

Flt = \new Voice {
  \set Staff.instrumentName = #"Flute" 
  \MyTranspose { \Basekey \FltPitches }
}
Trp = \new Voice \transpose bes c' { 
  \set Staff.instrumentName = #"Trumpet" 
  \MyTranspose { \Basekey \TrpPitches }
}
\score {
  \new StaffGroup {
    << 
      \new Staff { << \global \Flt >> }
      \new Staff { << \global \Trp >> }
    >> }
  \layout {}
}

% End of the example
% =============================================================
% The remainder is just for visualisation the deactivation of the
% transposition in a single snippet. You don't need this code in
% normal use...

\markup "The same without transposition:"
MyTranspose = {}

% The remainder is just a copy of the corresponding lines above:
Flt = \new Voice {
  \set Staff.instrumentName = #"Flute" 
  \MyTranspose { \Basekey \FltPitches }
}

Trp = \new Voice \transpose bes c' { 
  \set Staff.instrumentName = #"Trumpet" 
  \MyTranspose { \Basekey \TrpPitches }
}

\new StaffGroup <<
  \new Staff << \global \Flt >>
  \new Staff << \global \Trp >>
>>

\paper { tagline = ##f }