multiple time signatures

[Katie Ganem]

Hello,

I am trying to input a piece that has the vocal line in 12/8 but the accompaniment in 4/4 with the bars matching up.  I found this page in the manual that told me how to do this: http://www.lilypond.org/doc/v2.16/Documentation/notation/displaying-rhythms#index-time-signature_002c-compound

However, it doesn't seem to be working.  I hope someone can enlighten me on what I'm doing wrong.

melody = 

\relative c' {

  \clef treble

  \key g \major

  \time 12/8

upper = 

\relative c' {

  \clef treble

  \key g \major

  \time 12/8

  \set Staff.timeSignatureFraction = 4/4

    \scaleDurations 3/2

lower = 

\relative c {

  \clef bass

  \key g \major

  \set Staff.timeSignatureFraction = 4/4

    \scaleDurations 3/2

Thank you in advance!