you don't, you either work in audio PCM _or_ in MIDI from the set going...
however
a. you may try convert audio into MIDI (not in qtractor) to a varying degree of accuracy (mostly depends on the software tool _and_ the type of musical performance you're after, whether monophonic, melodic or harmonic, etc.);
b. you may try to split the audio clip into several, carefully cut-sliced on the onsets, move the clips around as far as to "manually quantize" as your liking on the timeline; then merge the moved clip parts back into one single audio clip; of course you'll have to be extremely careful to making the cuts preferably only on silent moments... unless you're targeting the "glitch" genre of production ;)
you don't, you either work in audio PCM _or_ in MIDI from the set going...
however
a. you may try convert audio into MIDI (not in qtractor) to a varying degree of accuracy (mostly depends on the software tool _and_ the type of musical performance you're after, whether monophonic, melodic or harmonic, etc.);
b. you may try to split the audio clip into several, carefully cut-sliced on the onsets, move the clips around as far as to "manually quantize" as your liking on the timeline; then merge the moved clip parts back into one single audio clip; of course you'll have to be extremely careful to making the cuts preferably only on silent moments... unless you're targeting the "glitch" genre of production ;)
byee