[Qtractor-devel] Strange behaviour of tempo changes

[David S. <da...@ae...>]

Although the Tempo Map/Markers window in Qtractor shows the position of
markers with an accuracy of 1/1000 of a beat, it seems that Qtractor
actually only permits tempo changes and markers to occur at beat 1.000
of a bar.  If any other position is specified, I find that the change
is placed at the start of the following bar.

For the type of thing I want to do this probably isn't too much of a
problem if I am recording new material.  But if I import midi tracks it
disastrously distorts the timing of the music, because in fact
Qtractor's behaviour is even more bizarre than what I have already
described.

Here is an illustration of the sort of thing that happens.  I have a
midi file of a saxophone quartet.  The original midi file was generated
by Lilypond.  The file was then converted to csv using midicsv, edited
to produce some needed tempo changes, ritardandos etc., and then
converted back to midi using csvmidi.

The file plays well in timidity, and I was able to generate an
acceptable mp3 from it.

But if I import the file (or one of its 4 tracks) into Qtractor the
tempo map and therefore the performance is complete nonsense.  Some
tempo changes are ignored and the rest are all placed on the first beat
of a bar.  But things are much worse still, because in most cases the
actual bar in which Qtractor puts a tempo change is the wrong one by
quite a large margin.

The first 10 lines of the tempo map as shown by Qtractor are these:

Bar  Time    Tempo Marker
  1  1.1.000 104.0 4/4
  2  2.1.000  77.0 4/4
  3  3.1.000 104.0 4/4
  6  6.1.000 109.0 4/4
  7  7.1.000 134.0 4/4
  8  8.1.000 159.0 4/4
  9  9.1.000 189.0 4/4
 10 10.1.000 200.0 4/4
 11 11.1.000 104.0 4/4
 20 20.1.000  84.0 4/4

If Qtractor were reading the files correctly, they should look like
this:

Bar  Time    Tempo Marker
  1  1.1.000 104.0 4/4
  4  4.1.000  95.0 4/4
  4  4.2.000  86.0 4/4
  4  4.3.000  77.0 4/4
  5  5.1.000 104.0 4/4
 13 13.1.000  97.0 4/4
 13 13.2.000  90.0 4/4
 13 13.3.000  83.0 4/4
 13 13.4.500 104.0 4/4
 14 14.2.000 109.0 4/4

Even if Qtractor does not like so many tempo changes in one bar, I
cannot see why it puts, for instance, the tempo change which should
happen at bar 14 at the start of bar 6.  The tempo change Qtractor
shows for bar 20 should actually occur in bar 50!

The fact that the tempo map quotes "Time" to 3 decimal places of a beat
suggests that Qtractor ought to accept a change at any time.  Perhaps
the design of the tempo map window is ahead of the current capabilities
of the program?

I emphasize that timidity reads this file perfectly satisfactorily and
responds to all the tempo changes correctly.

This appears to me to be a major bug, but perhaps it is just a by-
product of some other feature of the program.  In any case, is this
behaviour likely to be changed in the near future?

David