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Re: Terminology of baseMoment, beats, groups

From: Urs Liska
Subject: Re: Terminology of baseMoment, beats, groups
Date: Sat, 11 Nov 2017 12:00:48 +0100
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Am 11.11.2017 um 11:42 schrieb David Kastrup:
Urs Liska <address@hidden> writes:

So, now the first question ...

The terminology of baseMoment, beats and groups is inconsistent
between the NR
and the code. The question is, what are the components of the

   \set baseMoment = #(ly:make-moment 1/8)
   \set beatStructure = 3,3,2

 From the text in the NR this would be three beats, divided in three or
two base moments each.
However, the C++ code (and the code comments) refer(s) to that as
three groups with three beats each.
Can you please come up with actual quotes/evidence for those statements?
Neither of those make much sense, so I'd guess you'd been
over-paraphrasing either.  Or alternatively, there are grave errors in
the respective description which warrant fixing rather than unifying

a) from the NR section linked
"beatStructure is a scheme list that defines the length of each beat in the measure in units of baseMoment. "

I read this as: In the given example beatStructure is a list that defines the measure to consist of three beats. Beat one and two have the length of three baseMoments of 1/8, beat three is two baseMoments of 1/8 long.

Actually this is consistent with how I would describe that measure in prose: we have an 8/8 measure with three beats, with lengths 3, 3, and 2 quavers.

b) from

1) line 206ff., comment to find_location()
   Get the group start position, the next group starting position, and the
   next beat starting position, given start_moment, base_moment,
   grouping, and factor

2) line 265, comment right after find_location has been called:
// Mark the importance of stems that start at a beat or a beat group.

From the actual behaviour of the code (and other comments throughout the code) it is clear that "beat" refers to a baseMoment unit and "group" refers to the entity the NR calls "beat". The context property "beatStructure" obviously corresponds to the C++ variable "grouping".

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