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Old 06-11-2018, 05:58 AM  
schwa
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Join Date: Mar 2007
Location: NY
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OK. There are not surprisingly a couple of issues here.

First, Guitar Pro is exporting time signature changes in the instrument tracks, which is not standard, in fact I would call it an error. This is what causes the imported tempo markers to be one measure off -- if the Guitar Pro project had multiple time signature changes, I think the markers would be even farther off.

Second, there is no MIDI specification for gradual/progressive tempo changes. REAPER discretizes (stair-steps) gradual tempo changes when exporting. Guitar Pro just exports them as regular tempo changes, so you have to manually change them to be gradual changes when importing into any other software.

Third, REAPER does interpret gradual tempo changes differently from Guitar Pro. Consider a gradual tempo change from 120 to 80, over 2 measures.

In REAPER, the tempo change is linear over time, so the time used to go from 120 to 100 is the same as the time used to go from 100 to 80. This is correctly displayed as a straight line in the REAPER tempo envelope, because the timeline is always linear time -- one second of time takes up the same space on the screen, regardless of tempo. This works out to a total elapsed time of 4.8 seconds.

In Guitar Pro, the tempo change is linear over beats, so one beat is used to go from 120 to 100 and one beat is used to go from 100 to 80. This works out to a total elapsed time of about 4.87 seconds. This would be displayed as a curve on the REAPER timeline, not a straight line.

I don't think there is anything to fix on the REAPER side, although I will take a look at the time signature issue to see if we can adjust for what Guitar Pro does. Since there is no MIDI specification for gradual tempo changes anyway, it probably doesn't make sense for us to add a second method of calculating them.
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