Time signature conventions?

[Michael]

Hi,

I'm working on a midi sequencer, and am trying to determine the best way to
handle time signature messages in a midi file. In particular, how to
interpret the "bb" param of the time sig meta-event, as described in the
midi spec. This is the param that defines "the number of notated 32nd notes
in what MIDI thinks of as a quarter note (24 MIDI Clocks)".

I've been testing the behavior of Cakewalk Sonar (2.1), Pro Tools Free for
Windows and Emagic Logic 5.5 on OS 9. Cakewalk and Logic always seem to
disregard the "bb" paramter of the time signature. I've tested with time
signature of 4/4, 6/8 and 4/16 with different values for the "bb" param, but
they always play back with the tempo relative to a musical quarter note.
Technically, if I define, for example, the "bb" param as 4, the tempo should
be relative to an 1/8 note and not a 1/4 note. In Pro Tools, the files all
open up with the quarter note taking the beat for tempo's sake no matter
what the time signature "bb" value, but it can be manually overridden. In
addition, the midi clock output is always relative to a musical quarter note
as well, ie 24 clocks. In Pro Tools, if I change the note value that takes
the tempo, the clock count is _still_ 24 / musical quarter note, which then
makes things goofy, I think.

So is this some sort of de facto standard way of treating tempo of midi
files? ie to ignore the "bb" param?

Also, less importantly, Cakewalk and Logic ignore the "cc" param of the time
sig which defines the number of midi clocks per metrenome click, whereas Pro
Tools Free seems to honor it, albeit with one exception I find which is
possibly a bug.

Does anyone have experience with this, or maybe know of a detailed
discussion I could reference?

Many thanks,
Michael

[Clemens Ladisch]

Michael wrote:
> I'm working on a midi sequencer, and am trying to determine the best way to
> handle time signature messages in a midi file. In particular, how to
> interpret the "bb" param of the time sig meta-event, as described in the
> midi spec. This is the param that defines "the number of notated 32nd notes
> in what MIDI thinks of as a quarter note (24 MIDI Clocks)".

It's for _notated_ notes, so you can ignore it unless you want to
display/print a score.

> [...]
> So is this some sort of de facto standard way of treating tempo of midi
> files? ie to ignore the "bb" param?

Yes.

None of the parameters in the time signature meta-event affect the
playback of MIDI files in any way.


HTH
Clemens

[Michael]

"Clemens Ladisch" <clemens@ladisch.de> wrote in message
news:Pine.HPX.4.33n.0308291323120.5507-100000@studcom.urz.uni-halle.de...
> Michael wrote:
> > I'm working on a midi sequencer, and am trying to determine the best way
to
> > handle time signature messages in a midi file. In particular, how to
> > interpret the "bb" param of the time sig meta-event, as described in the
> > midi spec. This is the param that defines "the number of notated 32nd
notes
> > in what MIDI thinks of as a quarter note (24 MIDI Clocks)".
>
> It's for _notated_ notes, so you can ignore it unless you want to
> display/print a score.
> > [...]
> > So is this some sort of de facto standard way of treating tempo of midi
> > files? ie to ignore the "bb" param?
>
> Yes.

Thanks for the feedback, Clemens. Why though, does the definition of the
"bb" paramter include mention of a Midi quarter note being 24 clocks. Clocks
are only relevant during playback, not display. I'd thought that the word
"notated" was to mean "musical" to distinguish it from a _conceptual_ Midi
quarter note. Also, I haven't noticed that these programs display the files
differently on in the musical staff when the only difference is the "bb"
param.

In any case, since it seems like the standard is to always use (at least by
default) a musical quarter note for the tempo, then I'll just do that myself
as well.

Cheers,
Michael

[Clemens Ladisch]

Michael wrote:
> "Clemens Ladisch" <clemens@ladisch.de> wrote in message
> news:Pine.HPX.4.33n.0308291323120.5507-100000@studcom.urz.uni-halle.de...
> > Michael wrote:
> > > [...] the "bb" param of the time sig meta-event, as described in the
> > > midi spec. This is the param that defines "the number of notated 32nd notes
> > > in what MIDI thinks of as a quarter note (24 MIDI Clocks)".
> >
> > It's for _notated_ notes, so you can ignore it unless you want to
> > display/print a score.
>
> Why though, does the definition of the "bb" paramter include
> mention of a Midi quarter note being 24 clocks. Clocks are only
> relevant during playback, not display.

"What MIDI thinks of as a quarter note" is simply a unit to measure
time. The clocks are mentioned to distinguish the MIDI "quarter note"
(which is defined as 24 MIDI clocks) from a notated quarter note
(which may have a different length, as specified by bb).

> Also, I haven't noticed that these programs display the files
> differently on in the musical staff when the only difference is
> the "bb" param.

It seems this, and the metronome "cc" param, aren't widely
implemented. This is probably related to the fact that most MIDI files
don't use any other than the default values.


HTH
Clemens