thanks to all participating and trying to think this through. there are some tricky aspects to solve but i know some sort of implementation would be worth it.
Dandruff answered most everything I believe.
but i'll see if I can add anything...and please forgive me if i misrepresent/underestimate any current Reaper feature.
re:art,
1) Defining the in track region could be done by simple region/track selection then menu/key command toggle on/off. There could be a small bar, and similar functionality as the main loop region (ie., moving expanding etc)
2) The current Reaper function of defining loop regions is quite a bit slower when you need to drag the repetitions out in BOTH directions, plus to turn off the loop mode is to re-drag them back. To change to a new track-loop region is labor intensive as well when compared to say moving a visual loop region by drag and drop.
3) The loop region would override all other content on the track from beginning to end.
re:spon,
1)i would assume, but this might need to be further thought out, that the track loop would maintain its timing and not change if tempo changed later.
2) starting in "odd" places in time - yes track loops should figure out where they are.
3) loops not being on measure boundaries in my thinking is fine - and can be a very creative tool in itself enabling cool rhythmic cyclings. if the artist wants them to loop exactly then they define the region along meaures.
re: Enzyme,
1) as far as consolidating arrangement - i suppose there could be an option to create a new track or replace track with looped content. but let me say that this is not the primary goal of this feature.
More on why this feature is valuable. The real crux of the value is to be able to rapidly hear any part a linear musical sequence looped against any other part of the entire arranagment. If you make loop-ish music at all this is so indispensable.
An example:
Start with a few potential midi kick drum patterns on track 1. 1 on each bar, 1,2 3.
Loop bar 1 on kick track, and start improvising some midi snare hi hat combos on tracks 2 and 3. After about 20 bars of improvised playing, listen back. Isolate a few snare and hi hat riffs by looping them against Kick drum loop. Snare drum could be a 2 bar sequence, hi hat 4 bars... who knows but in each case rapidly one would be able to play them in time over kick on bar 1 without having to do labor intensive copy-pastes. In only a click or 2, Kick pattern 1 could be replaced with 2 or 3.
Now let's say a smoking drum sequnce has been created.
Plug in electric bass - improvise groove ideas over say 100 bars. Find 1,2, 4 ?? bar sequence that's tight and just right, loop that.
Perhaps as mentioned by Enzyme, perform a consolidation operation - we've created our core groove.
I don't know about you guys, but I am constantly working in this way - playing new parts over previous ones, and finding ideas out of longer sequences. But it is so hard to audition parts againast each other without committing to arranging elements linearly which is time consuming.
Perhaps the current Reaper functionality only needs a few tiny optimizations? Also I was having trouble at least in early versions where the dragged out loops did not "cover" other material on the track.
Let me add that as Enzyme says - Live' session window functionality is extremely useful as well - in a different way.
I think this feature should be thought of more as a utility in the process of groove and arangement writing, than something that is used at actual mix/render time. But the concept I believe is fundamental: why not be able to rapidly hear any timeline track region looped over any other?
Thanks again for all the brainstorming and questions