16 Dec
2002
16 Dec
'02
8:58 p.m.
On Monday 16 December 2002 21.21, Tim Goetze wrote:
[...]
I'm not sure if you absolutely need it (you *can* translate), but
indeed, it's *much* nicer when the "speed" of musical time depends
only on tempo, and not the whole meter. (IMHO, that x/y thing is
basically an irrelevant higher level grouping most of the time. Have
plugins ask for the meter info if they care.)
you're better off specifying tempo as quarter beats/minute
uniformly for the above reasons.
Quarter *note*, you mean?
(One usually says that 1 beat == 1 quarter not, so...)
Dunno about minutes, but hey, most people know how many seconds there
are in a minute, and it's THE standard unit for tempo, so people
probably go "Huh!?" if you say it's in beats/second. :-)
[...]
How about checking the audio sample rate? (Yes, that will not map
exactly to seconds, but it *would* allow you to have the same idea of
"1 second" as your wordclock sync'ed audio devices, which seems much
more useful to me.)
If you want to deal with *actual* wall clock time to do some I/O,
you're in the wrong thread (host audio thread) and/or asking the
wrong questions, I think.
Yes... Maybe. (Depends on what kind of calculations you do. Can't
think of any problems with beat sync effects, at least.)
Anyone here ever used non-integer # of beats/bar, and/or "weird" note
lengths?
i suggest
forgetting this. VST sets it to 1 PPQN, and treats "QN"
as "1 beat", so the information is really quite useless. there's
no need for it given TEMPO and METER.
you absolutely need ppq for the tick system to properly map
different measures (5/4 time, 6/8 time etc) as per previous
post. * units for meter (I don't know enough music theory
to answer
properly)
after much discussion about this on ardour-dev, we settled on
beats per minute, where beats are whatever unit the time
signature is using. for some music, the unit is irrelevant,
because nothing else uses subdivisions of the beat note value in
any coherent way (i.e. you can decide that a beat is a quarter
note, or a half note or a whole note, and nothing else will
care). for other music, its important that the beat value is
known. the TEMPO event
needs to include:
samples-per-beat (as a floating point value) [ time between
beats ] ramp slope (possibly 0) [ for accelerando and ritard ]
ramp target (irrelevant if ramp slope is zero) [ ditto ]
add seconds-per-beat for plugins that are not limited to
audio purposes. the METER event
needs to include
beats-per-measure (floating point value) [ 3, 5, 7, 9.5 etc ]
beat-note-value (floating point value) [quarter,1/16th, etc]
i wouldn't make either a float, it is by far too uncommon
to be justified and makes some arithmetic cumbersome. > "get current time information"
[...]
> "convert musical time"
[...]
from my experience, more conversion functions are needed, in
effect you need to map from any of these domains to any other:
* bar.beat.fractional (or .tick if you will),
Trivial if you have musical time and meter info.
* tick
Have TEMPO and POSITION_CHANGE Controls, and you'll be able to keep
track of that. (With subsample resulotion, except for the actual
timing of transients; those can only be sample accurate.)
* time in seconds
What time? Wall clock? If you have the current time info struct,
it'll contain that (as calculated by the timeline "driver", based on
audio latency), and then you can convert back and fort as you like
by, though musical time position/"tick".
* audio frame
That's our basic unit, so that's easy.
you may want to implement it using one call and a
structure
with flags denoting your interest,
That's what VST does. Might save some cycles.
or offer any of these as
a separate function. i have opted for the latter -- to keep
things sane, b.b.f conversion is only done for ticks and
vice versa though.
Yeah, it's just that that would be a *lot* of calls if you want to
cover all combinations. Look at VST's VstTimeInfo, or whatever Paul's
corresponding struct in JACK is called; those cover what you need.
//David Olofson - Programmer, Composer, Open Source Advocate
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