VstTimeInfo problem

Pollo · 02-07-2019, 05:54 PM

I am working on a plugin that relies on VstTimeInfo, specifically the value of ppqPos. This seemed to work well, until I started a project that had the (admittedly) uncommon tempo of 117 BPM. Now Reaper returns values for ppqPos that seem to be plain wrong.

To give an example: I have a project in 4/4, tempo is 120 BPM. I set the cursor at the beginning of bar 5. When I start playback, the first ppqPos value I receive is 32.00000000. This is right

Now I change the tempo to 117. Again I start playback at bar 5. Now the first ppqPos value I get is 31.999986394557823. That is wrong.

Is this a known bug?
How to deal with this? I can maybe use the samplePos value instead and calculate the exact beat position myself. But then maybe I run out of sync with the Reaper metronome?
You would think that it's not that hard to calculate this correctly. Why is it unreliable?

I'd appreciate any suggestions.

Pollo · 02-08-2019, 01:59 PM

Nobody has a solution? Well, I can understand. It's not easy stuff.

I did some more investigating. I thought I had a solution. I figured it might be some rounding error converting from float to int. But that didn't work out.

So now I'm trying to figure out how Reaper calculates the values I get from VstTimeInfo. It doesn't make any sense to me. Not only are the numbers off, they are not even consistent between themselves. samplePos doesn't seem to have a logical connection with ppqPos. The only common factor is that they are all wrong.
Worst thing is that I can't even find a work-around solution.

Must the conclusion be that it is impossible for a plugin to reliable sync with Reaper? Come on, Reaper. You are better than that.

snooks · 02-09-2019, 08:36 AM

It looks like it is lack of precision in floating point arithmetic. You can't reliably compare two floating point numbers that are the result of calculations directly because of this - you need to compare a range, in this case +/- around 0.00001.

schwa · 02-09-2019, 08:55 AM

Quote:

Originally Posted by Pollo

I can maybe use the samplePos value instead and calculate the exact beat position myself.

I believe that calculation will give you the same number.

Pollo · 02-09-2019, 05:24 PM

So any idea why it is not correct?

schwa · 02-10-2019, 06:39 AM

Because you can't have a fractional sample. It is reporting the correct PPQ position for the current sample position.

32 / 120 * 60 * 44100 = 705600 exactly
31.999986394557823 / 117 * 60 * 44100 = 723692 exactly

Pollo · 02-13-2019, 05:03 AM

schwa, you're right of course.

I solved the sync problem. It's working perfectly now. There was an error in my code.

Whenever I think Reaper is doing something wrong, it always turns out to be not true.