... well, Jerry's acoustics, to which I have nothing of much substance to add.
But I've been working on recording demos of a bunch of original music, and am faced with the hassle of trying to get a decent acoustic sound without dealing with mic placement, expensive condenser mics and challenged room acoustics. So, I checked out a Fishman Aura Spectrum DI box.
I'm pretty impressed with it. The Aura uses, I would guess, some sort of impulse response technology, where they are taking an actual guitar, miking it in a studio setting, and then convolving that recorded sound against the output of the same guitar over its built in pickup -- typically an undersaddle pickup (i.e., piezo). The result is you plug your guitar into the Aura and it spits out how it sounded when it was miked (they use various mics, a Neumann, Schoeps, etc., and you get several to choose from per guitar).
You can actually send them your guitar and they will mic it and create custom Aura files for you. Or, with the Spectrum, you can use one of the 84 onboard presets or go and download from dozens and dozens of guitars that they've sampled, as well as other acoustic instruments. They tell you the body style and woods, and so forth. You just download and try them out till you find one that sounds good with your own guitar if yours is not included in their archives yet.
My guitar was not included ... I have a Bob Weir Alvarez Yairi WY-1K in koa with the stock electronics. It sounds ... well ... buzzy and piezo-y on its own, much like Garcia's guitar sounded on the old Radio City recordings. But I did find a few settings on the Aura that sounded much better -- notably, one set of files made from a different Alvarez guitar that (presumably) had similar electronics.
A quick sample of a little capo'd fingerpicking on one of my new tunes ... first is the Alvarez into the Aura with the blend all the way off, so it's all straight guitar tone. Then it's the same guitar into the Aura with the blend all the way up. No difference in EQ, channels, effects, no compression, etc. on either guitar ... just straight up with a little stereo spread to it.http://52vincentdrive.com/aura.wav
Sounds a whole lot better, I think. Some guitars actually come with the Aura already installed onboard, and I would definitely look into that if you're in the market for a new guitar. I know Gibson is using it now. James Taylor sent his two Olson guitars to Fishman to have custom Auras files made and he's been using it live now.