OK, finally managed to get the 'advanced' chord demo (although I wouldn't call these advanced chords in the slightest ) to load... for some reason earlier today it wouldn't load.

First things first... that's a pretty low level, mix-wise, for the guitar part to sit at, IMO (I pay all that money for this feature, I would want it as loud as a real guitarist would be playing!). So, I think that the timbral changes are less apparent than they would be at a stronger level. But even as buried as that was, there is a VERY poor balance between the 'advanced' chords and the audio ones, to the point at times when it felt like the MIDI guitars were hardly there.

Also, there's a considerable difference in EQ between the audio track and the MIDI one. If there's a per-Part EQ, is it possible to 'tweak' the MIDI Part to be a better blend? More mids, for instance?

I guess if you never play those 'advanced' chords, you are set. Me, I can't think of a tune that doesn't have at least ONE of those, ahem, 'advanced' ( ) chords in it... For much of American music, at least, the guitar part is the driving force, the core rhythm of the style. To have such a disparity between different chords (especially as how Yamaha and Korg do it, to my ears, nearly equally well, and without ANY of the dropouts) kind of puts a damper on this feature. And, no offense, but this ONE feature is kind of the entire reason d'etre of the Audya.

It shows great promise, but I must confess, I think I can wait until it realizes that promise fully... In the meantime, both Korg and Yamaha are showing that you don't need audio loops to get very realistic style guitar parts, and there is room for advances in their approach that could take that approach even higher.

It'll be interesting to see what method eventually dominates. I can't help but root for the MIDI method, as much as I like to tweak my styles... Presets are great, but one bad match for a song, and with audio, you are screwed. With MIDI, at least there is the POTENTIAL (whether you take it or not is up to you) to fix the track...
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An arranger is just a tool. What matters is what you build with it..!