Re: ottava bassa

[Keith OHara]

> in the piano part of an ensemble piece i need (want, that is) to put  
> an ottava bassa indication that applies only to the lower chord in the  
> left hand. the problem is that at the same time a loco chord is tied  
> above it (see the attached image). 

This is awkward, because Lilypond applies the ottava to all the notes on the 
staff.  

This situation is similar to the problem of a pedal note, see <http://
lsr.dsi.unimi.it/LSR/Item?id=326> so I suggest you adapt that method.  
After starting the 8vb bracket, tell Lilypond to engrave as if middle C was 6 
steps above the centerline of the staff (that is, the normal position for 
middle 
C on the bass cleff). Then you enter the low notes one octave higher than they 
sound.

  << {
    \clef bass 
    <fis cis' g'>1  ~ | <fis cis' g'>4
  } \\ \relative c {
    r2. \ottava #-1
    \set Staff.middleCPosition = #6
    <b,! bes'>4 ~ | <b bes'>  \ottava #0
  } >>