https://forum.openmpt.org/index.php?topic=6154.0
The hard part will be figuring out the best way to have exact start and end loop points so that they match perfectly. As I understand it from what you say, if I do have exactly matching loop points, then the conversion to SFZ should work properly.I think there is a conceptual misunderstanding here. You try to make the left and right channels to be similar, but that is not necessary for a perfect loop. In fact, most of the time this will not be possible because the left and right channel will be out of phase (which is a big part of the stereo impression).
What's important is that the part before the loop end smoothly continues into the part after the loop end (i.e. the loop start), and it has to do so on both channels independently, i.e. the phase before the loop end must match the phase after the loop start (independently for L and R). The "on both channels" is the difficult part exactly because of the different phases. As an example, if you apply a slow chorus effect on the sample, the loop will only sound good if it repeats at a multiple of the chorus cycle's length because that's where the phases will be "in sync".
I think a good approach is to find a loop that is relatively good (i.e. both L and R phases match approximately at the loop start and end, but may still produce clicks) and then apply the loop crossfader from the toolbar to fix up the loop. Depending on the sample content, a very small crossfade (just a couple dozen or hundreds of samples) with the second slider all the way to left (constant volume) might already do the trick for fixing the click. Otherwise, a longer crossfade but with the second slider all the way to the right (constant power) might be better.
