OK, I'm reading a LOT of posts from people asking for features that already exist. Maybe on higher level arrangers than they own, but most of this is stuff that exists...
I really liked chas's suggestion for completely reconfigurable front panels. If you don't like the layout, change it! I'm not sure that the LEDs would really be necessary (and they would add a lot to the cost) because, if YOU went to the trouble of reconfiguring the front panel, you would probably remember exactly what you had done, but it is a great idea... And, it is ALL software. So easy enough for some manufacturer to implement. Probably every last one of us has sat and scratched our heads and gone 'why on earth did they put THAT button THERE? That's stupid...!" This would at least solve that problem. Nice one, chas...
OK... here are a couple of mine...
I LOVE the 'half time' button on Steinberg's Groove Agent drum software. One press, and whatever pattern you are playing gets a half time treatment. This is NOT just slowing the tempo down to 1/2 speed (for those of you that don't know what a 'half time' change is), but basically, the hi-hats or ride and probably percussion stay the same, but the kick and snare elements go to half time. It's a common trick for drummers and bass players, but I've never seen it on an arranger.
And I would still like to see the fills increased to one per transition. In other words, a completely different fill for each and every transition, AND a rotating fill-to-same. In other words, when you fill back to the same place, there are at least two fills that alternate. Getting away from the repetition of arrangers would be a lot easier, and I believe that style creation would be easier if you didn't have the problem of designing fills that transition smoothly to multiple destinations. IMO, that's one of the hardest things to do well on a style.
But anyway, keep them coming... Ideas that don't exist on ANY arranger, yet.
Who knows, maybe someone is reading this at an arranger manufacturer's R&D department...!
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An arranger is just a tool. What matters is what you build with it..!