16 Dec
2002
16 Dec
'02
5:01 p.m.
Paul Davis wrote:
you absolutely need ppq for the tick system to properly map
different measures (5/4 time, 6/8 time etc) as per previous
post.
well, if ppqn is variable, then sure. but cubase and all other vst
apps have defined it to be 1, which makes it irrelevant. their "pulse"
or "parts" (there seems to be disagreement over what the first "p" in
"ppqn" stands for) is not the same as the "tick" are discussing,
however.
so yes, ticks-per-beat is still necessary, but its a constant (1920 in
ardour).
* Host
sends buffers of N samples to plugins, with a starting timestamp
* Things send timestamped events to plugins
* Timestamps are measured in whole audio samples
* Host/timeline must export/deliver:
- SAMPLE RATE (samples/sec - passed at instantiation)
- TEMPO (sec/tick - event?)
- PPQN (ticks/qn - host-global? event? fixed?)
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. * 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.