lilypond-book and space between systems

[Luc Saffre]

Hello,

I am working on a songbook with 150 songs, mostly SATB settings.
Lilypond-book is really the only tool I can recommend for this type of
projects. Thanks for your work so far.

Now there are some scores where I'd like to increase space between
systems by 1mm. And lilypond-book ignores the parameters
`between-system-padding` and `between-system-space` in the ``\paper``
block. Hugo Ribeiro, Karl Hammar, Nicolas Sceaux and Alasdair McAndrew
have previously posted on this topic.

So I must use ``\betweenLilyPondSystem``. This seems logical since
lilypond-book somehow delegates the page layout to LaTeX.

Here is what I tried:

\newcommand{\betweenLilyPondSystem}[1]{\linebreak\vspace{1mm}\linebreak}

My problem is that this increases the space between systems by "1mm + 1
line", which is too much.

Another approach is to use the \linespread command:

  \linespread{1.5}
  (...(lilypond snippet here...)
  \linespread{1}

With this method, you don't specify a fixed absolute length to add
between the systems, but you specify a factor by which to increase the
line spacing. Maybe this approach is even better.

Unfortunately it doesn't work. I don't know why... my guess is that the
\linespread command has no effect on lines that contain a picture... I
also tried the setpage package, with the same negative result:

\usepackage{setspace}
(...)
\setstretch{1.25}
(...(lilypond snippet here...)
\setstretch{1}
(...)

So now I call for help! Is there anybody who has an idea?

Luc