Old 12-14-2019, 04:19 PM   #1
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Default Reaper glue bug - degraded output


What was expected?
- Render item as new take and/or glue should result in a rendered item that is just like the original (soloing that output phase-inverted with the original signal should cancel)

What happens?
- Rendering or Gluing an item results in a file that doesn't phase-cancel the original by a very large margin even when not using FX

- Reaper v6.01 @ Windows 10
- Affected tools: glue & render items as new take
- Affected lossless output formats: WAV (24bit) & FLAC (24bit)
- Sample rate: 48000Hz (for project & audio-interface & item sample rate, so no resampling needed)

Download the reaper project where this happens (too big to upload 15.5MB zip): https://drive.google.com/file/d/1eic...ew?usp=sharing

I've found a particular case where this consistently happens - If you use a snap offset on an item and render the item, the phase-inverted-glued signal doesn't cancel out the original one. However if I erase the starting tempo without snapping to the grid I'll have issues on other places! And the original parts with issues work right, where others that were ok start having trouble.

I've left a project with a track and its copy (if you play it you have no volume on the master as they cancel out of course).

Now just select the items on the track named "Copy" and glue them or render as new item: when you play it back, items that have snap offset work badly, specially the last item! (And if you erase the starting tempo without snapping to the grid and to the glue you have issues in other places!)

Please fix this, it's not a minor thing at all this bug. Thank you so much.

Last edited by AlbertoEAF; 12-14-2019 at 04:24 PM.
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Old 12-14-2019, 06:50 PM   #2
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I haven’t tested the project, but my guess is that it has to do with the items being positioned at fractional sample offsets, and the playback starting at different positions causing the output to vary by one sample. If you use the project setting to keep the grid sample-aligned, you can avoid this sort of issue.
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Old 12-15-2019, 03:30 AM   #3
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Hello Justin, that worked! Thank you so much!

Now the only part where this doesn't cancel out and generates some garble is at second 16, where there are stretch markers. Do you or anyone else know why?

Thank you,
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Old 12-16-2019, 05:47 PM   #4
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A word of warning - when using 'snap to project sample rate', items snapped to the musical grid will often (almost always in my experience) be a TINY bit off grid, only noticeable when zoomed right in. This is because it's snapping to the project sample rate, not the grid, obviously.

It's not enough of a discrepancy for anything to sound like it's out of time in real life use, but if this is a small sample like a kick drum that's going to be duplicated many times, you can find that after it's duplicated out (or looped) for a minute or two it will be slowly getting more and more off grid as that tiny length difference gets exacerbated with each duplication/loop, and after a while it will be a good few samples out, enough to cause phasing issues in certain situations, and after a bit more duplication it will start to feel like it's coming in early/late... it's easy to miss if you're not expecting it.

Reaper is such a flexible beast and I love it, but this is one of a small handful of situations where I would prefer the option to have it act like a more boring traditional DAW, and just force a global project sample rate, yes this would mean all imported media would need to be converted to that same sample rate, but I'm assuming this would help avoid this compromise where we have to choose between avoiding sub-sample edits, and correct accurate snapping to the grid. Perhaps I'm wrong though.

I'd argue most of us never need that sub-sample level of resolution anyway, besides people who want to combine lots of files of different sample rates in one project, but even then they're gonna have to pick one sample rate when they export and it ends up getting resampled in the end anyway - so why not just resample on import so everything is the same rate, and avoid these issues by locking the project to one sample rate (if in fact this would help to avoid them, which I'm assuming it would!).
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