turns out the "off by one sample" thing is due to pro tools being "sample rounded"
this means at certain tempos, certain bar|beat increments are decimel pointed
pro tools can't deal with that, so it rounds
this causes some edits to be off by a sample
to avoid any messing up during duplication and other operations, you are advised to use the selection tool instead of the grabber, because a selection doesn't have to obey the sample rounding rules
another alternative is to use relative grid mode with the grabber (for example, when alt+dragging to make a copy)
I just wanted to bump this because of some research I'm doing about sample accuracy in DAWs due to some issues with the Reaper system...
Pro Tools actually is one of very few DAWs that
is sample accurate, which is why you actually had this problem.
In Pro Tools, everything is on a sample grid. Which makes sense, because audio files are made of samples and audio playback happens at a specific sample rate.
So this creates a problem for "musical" grids like bars|beats. In 99% of tempos, a bar or beat is not going to be an exact number of samples. So to compensate for this, Pro Tools has to alternate in whatever pattern is necessary when building bars on the grid.
So for arguments sake, say the "perfect" bar length at a certain tempo is 7500.731 samples. Audio is based in samples and playback happens at a sample rate, so fractional samples are meaningless. So Pro Tools makes each bar alternate between 7500 and 7501 samples as necessary, since a bar can't be 7500.731 samples long.
Reaper and Cubase on the other hand ignore the sample grid.
THIS is a problem! These are the DAWs that actually "sample round". Pro Tools "bar rounds" (rounding bar lines to the nearest sample). In Reaper and Cubase, when audio playback happens it has to round everything to the nearest sample. So your audio
doesn't actually playback exactly as it appears on screen. So even though it "looks" like everything is accurate on screen, Pro Tools is the DAW that is actually more accurate because it doesn't deceive you, it plays back exactly what you see and it doesn't hide anything. If something needs to be rounded to a different sample, it will be shown that way in the edit window. In Cubase or Reaper,
it still gets rounded but you don't know it, it just gets rounded while playing back instead of on the screen!
Personally I would much rather have control over what's actually going to playback then have my DAW convince me everything is fine only to round behind the scenes.
Both approaches have their merit, but to complain about the Pro Tools system is unreasonable until you really understand everything.
In Pro Tools, one 16th note might be 500 samples, the next one will be 501 samples, then 500, then 500 then 500, then 501, etc. That's why things don't line up perfectly sometimes in situations like that, because
audio is sample based, so it only makes sense to make audio edits based on samples. Cutting a sample in half only forces the DAW to round on playback.
That's why if you trim a region in Pro Tools to be exactly one bar long, and then loop that bar for several loops, eventually it will be off by one sample in some of the loops because one bar can never be the perfect number of samples except at a very limited number of specific tempos.
So Cubase and Reaper are the sample rounders here, not Pro Tools.
Anyways sorry for the rant, but calling Pro Tools inaccurate or giving it a bad rep over this is not really fair...
Both systems have their advantages and disadvantages, but neither one is really wrong. There's no perfect solution, you just have to choose one set of issues or another.
