Did this for an album recently, the flex markers sometimes dont catch all the strums so youll have to manually insert some. Zoom in far so you can see all your meter divisions and snap to them easier. tedious, but it works
hope this helps
I assume that you mean manual flexing, not quantizing:
First, do not flex before you are ready with the guitar arrangement. If the guitar track is cutted, merge it to get one long region (!). Engage Flex, switch to "Polyphonic" and activate "Complex".
If the guitar is musically coupled to another audio track, hide the tracks between them and flex according to the waveform in the other track. This is better than working along the bar grid.
To correct a part, search for main strokes before and after this part, which are in time. Set flex markers there to restrict your corrections to this area.
If there are main strokes in the part to be corrected, do them first. Other strokes only if they are really wrong. If the whole track is out of time, try to shift it until it sounds reasonable and flex afterwards.
Do not correct every stroke because this will sound unnatural. Remember that a musician doesn't jump in time but rather drift forth or back. Therefore it is better to correct only the crucial strokes and those details that are clearly wrong.
You don't. The Guitar-Police will knock on your door and take you away
Well, I never had good results with quantizing acoustic guitar but I don't have typical rhythm tracks, so there are no regular peaks that could be used for an automatism. Quantizing does rather work for percussive sounds with clear regular peaks and not much between them.
You may try the quantize function and make it a little loose with the advanced settings ("Strength" less than 100%) but the result depends on the material and the transients Logic can find in the audio file. Mostly it finds too many in a guitar track and if you decrease the number of transients you easily lose some important bits.
A manual quickie might get you usable results:
Merge all regions on the track when your arrangement is ready. If you played in 4/4 set a flex marker at the first and then at every 4th beat. Not at the bar of the timeline but at the visible peak of the waveform. Pull each marker to its correspondending bar in the timeline. If that is not enough, do the same with every 2nd bar/peak. If this is still not enough and you continue on each beat, it will sound like a machine.
Another technique for simple rhythm tracks is to take a couple of bars, bounce them in place, flex them as good as you can and copy or loop them.
It's like catching the own tail - if you are a good guitarist and able to play a defined rhythm with clear attacks, quantizing may be successful but in this case you'll hardly need it at all. If you cannot play this way and would need quantizing, you make to much noise between the peaks and the quantize function does not work.
I also saw a great vid but not sure where now, but basically you convert the audio wav to sample and it comes up in EXS24 and on the piano roll and then you can quantize it and do wahtever the hell you want with it, you can make a drum template from your drums then force the guitar to play tothat groove template! It s pretty freakin amazin..