You wrote that even if I select the best Quantization Grid value (what does it mean?), it may still move some notes to the wrong gridline (apr 25th post in the end of text). Plus there "And the only way to fix that kind of thing is to move such notes by hand". Well, how do I know, what is a right gridline, and what is a wrong gridline? I have no idea. If I have no idea, how can I fix them by hand.. ?

The right gridline is the one you meant to play the note at. So if you intended to play a note at, say, the 3rd beat of bar 3, but you played it too early and it was closer to the 2nd beat of bar 3, then Quantization would move it to the 2nd beat of bar 3, which would be the wrong gridline, and after Quantizing you'd have to move it to the correct gridline [3rd beat of bar 3] by hand. The best Quantization grid is the value that corresponds to the fastest notes you played in the part you're about to Quantize. So if you played a drum beat that only has 8th-note hihats and quarter-note kicks and snares then the best grid would be 8th-notes; but if you played a part that also has 16th-note hihats, or, say, a 16th-note fill, then the best grid would be 16th-notes.

Let it make a crystal clear. For example, 3rd beat of bar 3 is the 3rd gridline.. ? Or where it lies.. ? I understand your explanation, only where are those 2nd and 3rd beats on a grid, as there are no names on the grid.. How to figure out? 4/4 means 16 squares is a full note and quarter notes are in every 4 bars a bit lighter vertical grids than other grids.

Part of the confusion here is that you're using some terminology loosely/incorrectly. - In 4/4 there is one whole note in each bar - In 4/4 there are 4 quarter-notes in each bar (4 quarter notes are the same length as 1 whole note) - Each quarter-note consists of 4 16th-notes (4 16th-notes are the same length as 1 quarter-note) - In 4/4 there are 16 16th-notes in each bar - The display of gridlines changes depends on how far you're zoomed in -- for example if you're zoomed out it may show only quarter-note gridlines but if you zoom in more it may show 16th-notes gridlines - The term "squares" has no meaning in musical terminology and is confusing In 4/4 the 3rd beat of any bar is the 3rd quarter-note in that bar. Again, this course should be helpful with the musical terminology and bar/beat designations: https://www.macprovideo.com/course/music-theory-109-music-theory-for-daw-musicians?afid=E470KLQ7r9

Well, the notes have their length. If I play on midi keyboard and don't play the notes on theirs exact length, will time quantize correct the length of notes, too? I mean, all quarter notes still be proper quarter notes as penciled in piano roll or as they are meant to be, not as I have (maybe occasionally, one shorter, another longer) played them on a midi keyboard.. ?

AFAICT GarageBand quantizes the start points of notes (the note-ons) but not the end points (the note-offs), preserving the durations of the notes as played.

What changes the duration of the played notes to the correct length? Does gb have any cure for inaccurate notes.. ? Or you already have answered for that in your last post.. ? Really no cure at all.. ?

AFAICT GB only seems to quantize Note-Ons, not Note-Offs. If you need to change the length of certain notes you'll have to do that by hand. Or you could step-enter the notes. But keep in mind that notes do not have to end on gridlines, in fact that's probably not desirable in many cases -- it all depends on musical content. As most musicians eventually discover, Quantization is not a miracle cure -- it's a useful tool for tightening up performances, but it can't do more than simply move the starts of notes to the nearest musical gridline.

So it's not a problem, if notes are not in theirs certain length? I can still get a good quality song with them.. ?

Of course notes don't have to be quantized, and there are no rules as to the lengths of notes. Timing considerations are all based on musical considerations -- quantization is just a tool to help people achieve tighter timing *if and when they need that*.