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Re: AU, plugin tempo, musical time information


On Nov 2, 2009, at 8:22 , Paul Davis wrote:

hi there. i'm the lead developer of Ardour and the original author of
JACK. i'm in the middle of implementing support for host callbacks in
Ardour's AU support, and the best documentation i've been able to find
so far on the data provided by the "getMusicalTime" callback includes
this paragraph:

For a change from 3/4 to 4/8 the value of the beat does not change
(thus, a 4/8 time sig will still have 2 beat values for that measure -
the value of the beat unit does not change as the time signature
changes). In common practise a beat is generally associated with a
quarter note. 

(from the documentation in the Developers/.../AudioUnits area)

This is quite a strange assumption. I've spoken to several experienced
musicians and this is absolutely the opposite of their sense of
musical time. If the meter shifts to 8, then a beat is an 1/8th note,
not a 1/4. If you were working on a piece entirely in 5/8 time, you
would not count in 1/4's but 1/8ths.

I think the docs are referring to common practice in software influenced by the design of Standard MIDI Files, not about what's common practice amongst musicians.

Think of a measure of 7/8 as being 3.5 beats long. This isn't the "canonical" way that a musician would think of it, but it makes perfect sense to a drummer contemplating polyrhythms, and it does have the advantage of a "beat" remaining constant in duration across meter changes (unless there are also tempo changes).

There is a meter track so it is possible to transform between the AU scheme and your own.

One other related question. the "getTransportState" callback includes
a field  to indicate whether or not the transport has changed. But the
documentation does not specify what it might have changed relative to.
The last callback?


I believe so but I'm not sure either.

Doug

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 >AU, plugin tempo, musical time information (From: Paul Davis <email@hidden>)



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