Time signature conventions?

Discussion in 'comp.music.midi' started by Michael, Aug 29, 2003.

  1. Michael

    Michael Guest

    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
  2. 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
  3. Michael

    Michael Guest

    "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
  4. 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

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