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Re: Issue 1776 in lilypond: Doc: NR - Polymetric Notation \compoundMeter


From: lilypond
Subject: Re: Issue 1776 in lilypond: Doc: NR - Polymetric Notation \compoundMeter isn't documented
Date: Wed, 03 Aug 2011 05:22:07 +0000


Comment #11 on issue 1776 by address@hidden: Doc: NR - Polymetric Notation \compoundMeter isn't documented
http://code.google.com/p/lilypond/issues/detail?id=1776

James,

i hoped to answer sooner but i had to fight problems with grand-fixcc.

2011/7/31 Comment #9 on issue 1776 by pkx166h:
However, because I am curious (and don't a thing about this special
notation) can you tell me why

\relative c' {
  \compoundMeter #'((1 4) (3 8 4))
  \repeat unfold 5 c8 \repeat unfold 10 c16
}

This one is perfectly ok and compiles for me.

\relative c' {
  \compoundMeter #'((2) (3 8 4))
  \repeat unfold 5 c8 \repeat unfold 10 c16
}

You cannot have only one number in parentheses.

Fails? and why I get a different error for each case?

Id kind of expect

\compoundMeter #'((2) (3 8 4))

to be equiv of     2
               3 + 8 + 4

Is this not allowed in music?

Or at the very least 2 + 2 + 2
                     3   8   4

Maybe this is an enhancement?

Again as an example

  \compoundMeter #'((1 4) (3 8 4))

could be the same as 1 + 4 + 4
                     3   8   4

I hope this makes sense?

I'm afraid not... It looks like you're reading the syntax in the wrong way. I'll try to explain it in more detail (hoping that i understand it correctly myself ;).

Time signature tells musicians how many beats are in the measure and what is their length. Ordinary time signature is like a fraction: \time 3/4 says "there are three beats in the measure, each beat has a length of a quarter note", \time 8/8 says "there are eight beats in the measure, each beat has a length of an eight note" and so on: the numerator of the fraction says how many beats are in the measure, and the denominator says how long they are. Now consider a piece written in 15/8 (this surely is a strange meter!). It tells that there are 15 eight notes in the measure, but how the musician is supposed to play it - how will he subdivide the measure? (for example, a 6/8 measure is divided into two groups, each consisting of 3 eight notes: *one* two three *one* two three). What is the composer's intention in case of 15/8? That's where \compoundMeter comes to rescue: one can write \compoundMeter #'((4 4 4 3 8)) and the musician will know that he should play it like this: *one* two three four *one* two three four *one* two three four *one* two three

writing \compoundMeter #'((3 3 3 3 3 8)) would mean to play it like this:
*one* two three *one* two three *one* two three *one* two three *one* two three

Now imagine a meter in which beats have different length. For example, first beat in the measure is a quarter note, and second beat is a half note. How are you supposed to write this? The measure length is 1 quarter + 1 half = 3 quarter notes, but you cannot write \time 3/4 because that means "three beats, each one quarter long". \compoundMeter #'((1 2 4)) wouldn't be accurate, too. You need to write this time signature as 1/4 + 1/2 - this is accomplished with \compoundMeter #'((1 4) (1 2)) .

So, using the "fraction" nomenclature, \compoundMeter #'((2 3 4)) produces a single fraction (with the numerator consisting of two numbers: 2 and 3), while \compoundMeter #'((3 8) (2 4)) produces two fractions (3/8 and 2/4). Notice where the plus sign is located in each case. As you can see, each parentheses inside \compoundMeter #'( ) corresponds to a separate fraction in the final time signature; \compoundMeter #'((3 8) (1 2) (4 1 4)) will be made of 3 fractions. If you write \compoundMeter #'((2) (3 8 4)), you are telling Lily "do a complex meter consisting of two fractions: first fraction will be made from number 2, second fraction will be made from numbers 3, 8 and 4" - while one number (2) is not enough to form a fraction: at least two numbers are necessary for a fraction!

Maybe it would be good to include some of this explanation in the patch?

I just want to know what the limitations there are and if these are
@knownissues or bugs or something else I need to document.

I thought i found one, but now it seems to works... It seemed that \compoundMeter wouldn't accept irrational meters (for example \compoundMeter #'((1 3) (1 4)) ), but now it works... Strange.




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