Fit To Time error

Recently I and forumite brundlefly had discussion about Tempo Offset (or Scale) feature. brundlefly drew my attention to some very strange phenomenon. Here I'll try to illustrate his discovery with my screenshots.

1. Let's say we have some project with midi track. There are three sections: A goes 100 bpm, B 120 and C 140.



2. We change tempo of section B from 120 to 130 bpm. Ending time of Section B changes too and it's 00:00:49:09 now. Let's remember this number.



3. Now we undo our tempo change and reverse the process. We select whole B section and go to Process > Fit To Time command. In New Thru field we enter new time from the previous step, which is 00:00:49:09.



4. We expect new section B ending time to be 00:00:49:09, as we ordered, and tempo of Section B to be 130 bpm. But what we see is very strange.



New time is 00:00:49:16 instead of 49:09 and tempo is 128.81, not 130. Section C tempo changes also to some wrong number.


All this shows that Fit To Time command is unreliable. It "fits" time to some values which are different form what you expect.

Very nice job explaining and illustrating the problem, Vladimir. I too hope that the bakers will take a look at this and fix it. I played around quite a bit with the numbers Sonar was producing with different scenarios, and could not figure out - or mathematically reproduce - what it was doing wrong, but it's definitely not working properly, and it's not an insignificant rounding error.

Incientally, Valdimir, if you haven't logged this as a formal bug report via the Cakewalk Problem Report Form, you should. You can refer them to this post for reference. Otherwise, they may never notice this.

http://www.cakewalk.com/Support/ProblemReporter/

Small point, but if you move the position of the 3rd section's tempo one tick later, it will be be out of the selected range. You'll get different result for the 2nd tempo, but the 3rd one will remain at 140. I tried this on S5PE and it recalculated the 2nd tempo as 145.55.

Now try this: remove the 120 tempo entry, make sure the 140 tempo is at 25:01:001, highlight the same section 10-25 and enter 49:09 for the new ending time. It calcs the tempo at 129.96....close, anyway.

The problem is that the absolute ending time of 49:09 is influenced by the fact that the first 9 bars are at 100bpm, even though they're not in your selection. If you want it to recalc the selected section, you need to remove the 2nd tempo. It will recalc the tempo for the selected section.

Right. It looks like the calculation is peformed on the basis of seconds and frames (1/30th of a second or 0.033333...). The selected interval is changed from a length of 36 seconds to a length of 27.7 (49:09 - 21:18 = 27:21 = (27 + (21 * 0.0333333...) = 27.7 seconds. The tempo is then (36/27.7) * 100bpm = 129.96bpm.