Jerzy,
Why do you want to specify time in ticks rather than seconds or
beats? I think of ticks as an implementation detail to allow fractional
beats such that:
- floating point is avoided (this was important on early PCs)
- representation is compact (by limiting precision)
- rounding errors can be avoided with quantized beats in simple
ratios such as triplets
None of this sounds particularly important in modern systems, and the
Allegro/PortSMF
library factors out ticks while midi files are being parsed.
I ask because if there's really a good reason for using ticks, then
it would make sense to put the original ticks/beat number into the
sequence or track structure where it could be used.
If the goal is just to have access to fractional beats or seconds,
that's why time is a double.
> If I want a sequence with the first tick [you mean from tick 1 to
tick 2? -rbd]
> of a MIDI file at 480 PPQ and 60 BPM am I to
> call:seq->cut(0.0020833333, 0.004166666, false)?
Why not call seq->cut(1.0/480, 2.0/480, false)? But then wiring 480 into
the code is obviously not right, hence my question.
I would tend to write the play code to seek into the track or
sequence (there's an iterator to help do this) rather than cutting out
and copying the stuff I want to play. I think it's cleaner, and there's
also the issue that MIDI is not stateless -- when you play from some
random time point, do you want to first set all the prior program
changes and control changes? Usually, sequencers just spew out
everything but note-on and note-off commands, starting from the
beginning of the sequence so that when you start playing notes, all the
control values are correct. You could do something more sophisticated,
but it's quite tricky to build efficient and editable structures that
let you find the last control change for each possible control.
Feel free to follow up with more questions or details -- this is a
pretty open-ended question.
-Roger
PS This code was extended with a lot of editing operations for Audacity.
It's not in Audacity yet, but we're working on it actively right now, so
you're likely to see some activity on the project as we fix bugs and
extend functions as needed. Parts of this code have been used a lot, but
most of the editing functions like cut() and selection functions have
only received some basic testing.
Jerzy Gangi wrote:
> Hi,
>
> First, I'd like to thank everyone involved for developing the
> portmedia libraries. I have found these libraries very useful, and I
> appreciate the effort you all put in to the portmedia project.
>
> I am trying to create a playRange(seq, ticks_from,ticks_to) function,
> similar to the seq_play(seq) function in allegroplay.cpp. The function
> will take in a range of the SMF's ticks, relative to tick 0 at the
> beginning of the file, and play from the beginning of ticks_from all
> of the way through the end of ticks_to. For right now, I am extending
> allegroplay.cpp, which is making this easy to try out. (thanks to
> whoever prepared the xcode project file). I should mention that my
> driver will not be calling playRange at "pretty" music intervals (eg
> playRange(seq,233,475)), else I'd just use cut() to cut the sequence
> inside some range of beats. Therefore, tick, not beat or second,
> precision is necessary for my playRange().
>
> My first idea was to use Alg_seq's cut(double start, double len, bool
> all) method. If I could cut away the range I don't need from a
> sequence, I could play the resulting range with
> seq_play(the_having_been_just_cut_seq). Right? However, cut() only
> lets me specify in terms of beats (as a double) or seconds, the unit
> being settable on the object. If I want a sequence with the first tick
> of a MIDI file at 480 PPQ and 60 BPM am I to
> call:seq->cut(0.0020833333, 0.004166666, false)? See? I think I want a
> tick-based function. I tried a few other things, but a stumbling block
> was that get_dur() returns 0 for me.
>
> I did not see very many public functions in Allegro (which I have to
> say is designed pretty nicely!) that use "ticks". I assume these
> classes were designed to favor musical intervals over ticks. This
> would make sense, and what I am trying may be very well against the
> intended usage of the allegro/portsmf classes.
>
> Any advice on if I should subclass / use the fractional beat unit /
> not be using portsmf, etc. is 100% welcomed! I hope everything here is
> understandable; I'm happy to elaborate on anything.
>
> THANK YOU!
>
> Jerzy Gangi
> Computer Music Department, Peabody Conservatory
> Johns Hopkins University
> _______________________________________________
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> [email protected]
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>
>
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