normalshapemediumseries\defnormalshapemediumseries\staffspacingii{ 0.75}
before the starting command normalshapemediumseries\debutmorceau.
Not only does this statement change the vertical spacing between staff lines, but is also changes the size of the key, accidental and note symbols to fit the modified staff line spacing. However, the existence of discrete font scales for music symbol typing results in some reasonable restrictions of the values of normalshapemediumseriesnormalshapemediumseries\staffspacingr : recommended values are approximately 1, 0.8 and 0.64; if different values are chosen, then the symbol size is taken smaller than the line spacing, which may lead to readable but rather ugly typesetting.
As an example, we give two bars of the Ave Maria by Charles GOUNOD using the first prelude of Johann-Sebastian Bach's Well Tempered Clavier (transcription for organ, violin and voice, thanks to Markus VEITTES):
This example was coded as:
\def\nbinstruments{4} \sepbarrules \generalmeter{\meterC}\relax \def\oct{\advance\transpose by 7\relax} \def\staffspacingii{0.64} \def\staffspacingiv{0.64} \cleftoksi{{6}{0}{0}{0}} \cleftoksii{{0}{0}{0}{0}} \cleftoksiv{{0}{0}{0}{0}} \nbporteesi=2\relax \nbporteesiii=0\relax % \debutextrait \normal\elemskip=0.02\hsize %Takt 9 \Notes\zhl c\raise27pt\qs\qupp e|\ds&\oct \itenu5h\hl h&gra---&\itenl4h\hu h\enotes \Notes|\ibbl0j3\qb0h\tqb0l\enotes \Notes|\ibbl1k0\qb1o\qb1h\qb1l\tqb1o\enotes \temps\Notes\zhl c\raise27pt\qs\qupp e|\ds&\oct \tten5\ibl4c0\qb4h&&\tten4\ibu5g{-3}\qh5h\enotes \Notes|\ibbl0j3\qb0h\tqb0l&\oct\qb4a&---&\tqh5a\enotes \Notes|\ibbl1k0\qb1o\qb1h&\oct\qb4b&ti-&\cu b\enotes \Notes|\qb1l\tqb1o&\oct\tqb4c&a&\cu c\enotes \barre %Takt 10 \Notes\zhl c\raise27pt\qs\qupp d|\ds&\oct \qlp d&ple---&\Ilegu4k\pt d\qu d\enotes \Notes|\ibbu1g3\bigaccid\qh1{^f}\tqh1h\enotes \Notes|\ibbu2i0\qh2k\qh2f\enotes \Notes|\qh2h\tqh2k&\oct \cl e&&\tleg4\cu e\enotes \temps\Notes\zhl c\raise27pt\qs\qupp d|\ds&\oct \ql d&na,&\qu d\enotes \Notes|\ibbu1g3\qh1f\tqh1h\enotes \Notes|\ibbu2i0\qh2k\qh2f\qh2h\tqh2k&\qp&&\qp\enotes