Lilypond - autochange with alternative staves / turning point

Question

I want a single voice drifting across two staves, and I want LilyPond to automatically decide which staff to use.

(As can be seen here) For treble and bass clefs this is easily implemented with the \autochange command:

\version "2.18.2"
\new PianoStaff 
<<
    \new Staff = "up" {
        \clef "treble"
        \autochange {
            c,4 e, g, b, |
            d f a c' |
            e' g' b' d''|
        }
    }
    \new Staff = "down" {
        \clef "bass"
    }
>>

---

But (as I'm transcribing guitar), I want to use suboctave clefs (treble_8 and bass_8).

When I try this ... :

\version "2.18.2"
\new PianoStaff 
<<
    \new Staff = "up" {
        \clef "treble_8"
        \autochange {
            c,4 e, g, b, |
            d f a c' |
            e' g' b' d''|
        }
    }
    \new Staff = "down" {
        \clef "bass_8"
    }
>>

... LilyPond is still assuming that the turning point is at middle c (c'), and not at the appropriate c below middle c (c):

---

I know I could just change staff manually. But
is there a way to get LilyPond to use the \autochange command correctly with the alternative staffs or with an alternative turning point?

Answer 1

Do you insist on using version 2.18? 2.19 can do it without trouble. You just have to stick the turning point just after the \autochange. So instead of \autochange { music }, you would use \autochange c { music }. This is what my Lilypond 2.19.62 does when I do that with your example (otherwise copied verbatim):

\version "2.19.62"
\language "german"

\new PianoStaff 
<<
    \new Staff = "up" {
        \clef "treble_8"
        \autochange c {
            c,4 e, g, b, |
            d f a c' |
            e' g' b' d''|
        }
    }
    \new Staff = "down" {
        \clef "bass_8"
    }
>>

(It looks a bit different because I use different fonts, and the B's come out as B flats because I use \language "german". But otherwise it's all good.)

(Also don't let yourself to be put off by the fact that 2.19's are the "development" version. They're in fact very stable. I use it a lot and during those couple of years, it has crashed on me only once.)