=head1 NAME

Octaves --  how to do pitches

=head1 DESCRIPTION

The LilyPond input language, Mudela (help, silly name), should be easy
to read and write.  In my experience Mudela is already quite convenient 
for entering music.  Every time i've entered a substantial piece of music, 
however, i found that i made quite a few mistakes.  The MIDI output helps 
a lot with locating and correcting the errors.  There's one type of error 
that seems to be frequent, stubborn and hard to catch, and that's the
octavation error.  The relative octave feature is an attempt to make
Mudela a bit easier to write.  In addition, this featuer makes it harder 
to make octavation mistakes, yet if you made one, its a lot simpler to find 
and correct.

Here's how it works.  

=over 5

=item * 
forget the old "\octave c';" command

=item * 
forget the old octave boundaries with octaves c .. c'

=back

You start the relative octave mode (for now) with the command

    \octave relative;

From then on, the pitch of a note will be the closest to the last one,
assuming that large intervals are a lot more rare than small ones. 
Thus, you can enter a scale without using octavation quotes:

    c d e f g a b c

the last c being an octave higher than the first.  If you have to
enter an interval that is greater than a quart, you must specify
whether the pitch goes up, using post-quotes:

    c c' % octave up
    c g' % quart up 

or down, using pre-quotes:

    c 'c % octave down
    c 'f % quart down

Although it is not necesary, and thus redundant, information to specify
the direction of smaller intervals, you are allowed to do so:

    c d  % second up
    c d' % second up

    c a  % third down
    c 'a % third down


=head1 CONVERTING

To convert a piece of music from the old absolute-octave notation to
relative octaves, lilypond provides the B<-f, --find-quarters> feature
to locate all big intervals in your music (sorry, fully automated convert 
is too complex).

You'll do something like this:

    lilypond -f los-toros-oboe 2>&1 | tee intervals
    ...
    los-toros-oboe.ly: 59: warning: Interval greater than quart, relative: d':
        [)g8  r d
                 '] r |
    los-toros-oboe.ly: 100: warning: Interval bigger than quart, relative: d':
	[d8 d
             '] [es'8.-> c'16] |
    ...

Then you load a copy of the original mudela file in your favourite editor, 
and let it parse the 'error file' F<intervals>.  First you remove all 
octavation quotes.  Then, jumping from warning to warning, you enter quotes 
as suggested by LilyPond.

=head1 EXAMPLE

See F<mutopia/ltor.ly>.