njaohnein - thats a real hazzle and thats where so called 'acid-fyed' loops come in. Loop-trackers was the brain-child of acidMusic. Their tracker got a real hype and well earned success in late 90'. I got my copy with an external HD, and i really didden knew what it was, before a out of boredom one day took a look at the bundled software.. and it was a cutie!
Sadly SONYmusic liked the software too, and bought acidMusic. Emediately all promises of life-time upgrades and cool new packs for dl was scratched :/
*sighy*
...enough memories :p
In lmms there may be a new feature 'later'. I have thought about a method for adding a tracker with exact looping of any sample over n bars, and lmms almost have the architecture for it already! Right now lmms handles samples badly, -especially
sample-track, but it will improve ..'later' :p
But @trewqazwer, the only option is to record your loop to fitting size in another program like audacity, and then use
that file in your project
http://audacityteam.org/