Re: understanding midi files

[pls]

On 28.01.2014, at 12:24, address@hidden wrote:

> http://www.cdik.se/pdf/midiformat.pdf describes the time signature
> event on page 12. It is unclear written. Is there anyone here that
> have a clear understanding about the last two parameters, named cc and 
> bb in the document ?
> 
> And page 4 describes "ticks per quarter-note" where the "quater note"
> isn't nessesarily a quarter note.
> 
> The text says something like
> 
> cc    number of ticks in metronome click
> bb    number of 32nd notes to the quarter note
> 
> So if I have a 6/8 key signature, the beat is two per measure (on 4.
> in lilypond notation), but the text confuses the reader with
> expressions like "quarter note", "MIDI quarter note" and
> "metronome click". Where obviously the "quarter note" isn't a normal
> quater note.
I don't agree.  I read it the following way (p. 4 and 12): 
cc:
there are two formats of dividing (delta) time: metrical time and 
time-code-based time.  The former is measured in divisions / ticks / clocks of 
a quarter note.  (A quarter is always a quarter note.)  "For instance, if 
division is 96, then a time interval of an eighth-note between two events in 
the file would be 48."  This means that a dotted-quarter note includes in this 
case 144 (96 * 1.5 or 48 * 3) ticks / clocks. If the divisions value for a 
quarter note is 24 than the number of MIDI clocks in a dotted-quarter note is 
36 (24 * 1.5 or 12 * 3).

bb:
"The bb parameter expresses the number of notated 32nd-notes in a […] quarter 
note […]."  (I left out the word MIDI because it confused you.  Just think of a 
normal quarter note.)  If you would like to notate quarter notes than bb equals 
to 8 (8/32 = 1/4). If you want to notate eighth notes than bb should be 4….

I found a footnote in Beyond Midi – The Handbook of Musical Codes (Ed.: E. 
Selfridge Field, 1997, p. 54) which might be helpful to further illustrate the 
bb parameter. The footnote also shows the (MIDI) limitations of subdivising 
quarter notes by 32nds:

The intention of bb is to allow for the distinction between duple and triple 
subdivisions of the beat.  Multiple mixed compounds (duple at one level, triple 
at the adjacent level) are possible.  However, 32 is not a large enough number 
to handle multiple rhythms of any significant complexity. For example, in the 
duple subdivision of the quarter note, an eighth note would be equivalent to 
four 32nd notes;  a sixteenth note would be equivalent to two 32nd notes, etc.  
For triple subdivisions of the quarter note, 48 and 96 are more convenient 
numbers to use, and in the classical repertory many instances are encountered 
in which still larger multiples (or, in other file formats, floating-point 
arithmetic) are required for clarity and accuracy.

hth
patrick