Pardon my butting in but if you are an OpenMPT user why would you wanna break out cash to learn either of those big pigs ableton or FL? Surely there is a VSTi-VST solution to whatever you are trying to achieve that would work in OpenMPT I assume as I don't use OpenMPT (can't stand it) but others like it...
You soon would be trying to learn new garbage & probably get lost & not do anything with it... I tried ableton a number of times in the past not a good fit & most everything I was hearing from others sounded like they were using the stretching & other feature to obtain a 'happy accident', then loop that & apply tons of mind-numbing FX & call it music...
Or are you looking to stretch loops for backing tracks? Many ways to obtain such... Recently I wanted to do that in Skale Tracker as Skale sounds great with HiQ AKAI instruments (as good or better than renoise XRNI) So I thought acrobatics EGO Pad would be great but Skale won't run it so I ran it through the old Phrazor beta matching BPMs (Skale has no plugin tempo sync)... So then combined that with a power chord AKAI & simply drawing 3 different track FX in the track editor produced-
https://alonetone.com/TalkOrBell/tracks/skale-akai-phrazor-egopadProbably not what you are looking for but most would not think what I did was possible in Skale I'm SURE there's much that can be done inside OpenMPT to boggle the mind...
