Re: NR 1.2.3 Upbeats: confusing explanation of measurePosition

[Trevor Daniels]

Federico, you wrote Sunday, December 30, 2012 10:59 PM


> In NR 1.2.3, Upbeats:
> 
> """
> So \partial 8 becomes:
> 
> \time 3/4
> \set Timing.measurePosition = #(ly:make-moment -1 8)
> e8 | a4 c8 b c4 |
> 
> _The property measurePosition contains a rational number indicating how 
> much of the measure has passed at this point_. Note that this is set to 
> a negative number by the \partial command: i.e., \partial 4 is 
> internally translated to -4, meaning “there is a quarter note left in 
> the measure.”
> """
> 
> IMO the first sentence is a bit confusing.
> What the number says actually is "how much of the measure is needed to 
> complete the time signature", 1/8 in the example above. This implicitely 
> says how much of the measure has passed at this point: 3/4 - 1/8 = 5/8

Because the time in the measure is calculated modulo the time
signature the position -1/8 is the same as 5/8 in 3/4 time.  But -1/8
is at position 5/8 in the /previous/ bar.

The text tries to explain what \partial does, which is count backwards
over the anacrusis.  If you set measurePosition to 5/8 it looks the same
as it does when set to -1/8, but the bar numbering will be 1 off.

Trevor