Step 1: Get Your Stuff: Nomad
With a little shopping around, however, one can put together a unit that meets requirements. This is possible for one reason, and one reason only: the Creative Nomad Jukebox 3. This product, long discontinued, is the result of audio engineers known mostly for their sound cards, interfaces and other geek toys being turned loose on the consumer mp3 player market. The resulting device is the antithesis of the iPod: heavy, built to resemble a portable CD player, and covered with ports: a headphone port, two line outs, and a line in that accepts optical and 1/8", FireWire, USB, 5vDC and IR port (turn this off). It is that optical port that enables the one function which makes this the Must Have Item: the njb3 records optical 16 bit signals as .WAV in 48 and 44.1 kHz stereo. Hallelujah.
The njb3 has other key advantages: it comes with one lithium ion battery pack, but can be converted over to two, giving an actual six hours of record time. Equally cool, it has a standard 2 1/2" laptop style hard drive and can be easily upgraded. The stock 20 gb is good for 30 hours or so of .WAV, and it's all capacity from there.
The optical port is the main thing, though. Many mp3 players, including the njb3, can record line-in sound or even provide a preamp. The resulting recordings suck: the A/D converter is the cheapest one they can find, and rightly so, since the hard drive noise is going to ruin your recording anyway, as will the electrical noise. This is not the way; although this rig will allow you to run in a 'stripped down' mode that looks a whole lot like listening to a CD player, the quality must be improved by an outboard AD converter in order to meet our spec.
The njb3 is no longer produced, but many new-in-box units exist and creative still sells batteries off and on...someone will eventually pick up an aftermarket for these batteries if Creative drops the ball, because as the eBay price for a used one will show you, these puppies are coveted. As for other mp3 players that can do the trick, Neuros is waffling on a digital in for the Neuros 3. Express your preference that they do this, because then we will have no longer to deal with the quirks of a long out-of-production proprietary codebase. There are no other contenders, to my knowledge. Your Nomad should cost around U$300.
Step 2: Get Your Stuff: A/D and Preamp
Edirol UA-25. This is larger than the other two units, but provides a great deal more functionality; if stealthiness is the concern, go with one of the other two, but for function you can't really beat the UA-25. It isn't actually cheaper by much, when you factor in the higher-priced (and quality) 48v phantom mikes, but then you have better mikes which are more able to handle loud sounds while remaining useful for very quiet ones.
The UA-25 runs off USB power, and thus we used to have to make do with post-manufacture modified units, made by experts or homebrew. However, this instructable details making a perfectly good power supply for the UA-25: Portable USB Charger. If I had my system to do over again, I might well go this route...you save a component, also, as you don't need a battery box. It can output up to 96 kHz stereo at 24 bits, but your Nomad will choke on this: it is useful functionality for later upgrades, though, as the Neuros 3 is expected to support 24/96 as a native type. U$250-ish.
Denecke AD-20. This is the one I've got. Made for the movies, it's bombproof and simple: when the battery is flipped one way it's off, when it's flipped the other way it's going. There are gain knobs, left and right. It takes XLR so either you need XLR mikes or a converter cable (as shown and more likely). Outputs 44.1 kHz stereo at 20 bits, for technical reasons that amount to a natural truncation of the noise floor without creating aliasing at 16 bits. Outputs optical and coaxial digital. Cannot break it. About U$350.
Your other good option is the Core Sound Mic2496. As you'd guess, it supports 24/96 native, and is designed to be paired with their custom phantom power supply and binaural microphones. Isn't any better than the AD-20 for attaching to the Nomad, but better for attaching to the vaporNeuros; also bombproof. U$550.
Step 3: Get Your Stuff: Mikes and Power
A note: the Edirol will power your mikes, at 48v Phantom no less. That means you have to spend your savings on better mikes, but hey, you now have better mikes, and you eliminate part of the train, which is nice when it comes time to pack it.
Expect to pay a minimum of U$100 for your mike and homebrew battery box; a couple hundred to do it right up to more for hand-selected quality phantom mikes.
Step 4: Record Stuff
For unobstrusive recording, I like to pack the whole unit down into a hydration bladder type backpack, with the microphones routed through the tube hole and clipped to the straps. I'd show a picture but my hydro is covered in playa dust and has a huge hole in it from overpacking while in Asia. I've used this rig to record in Thailand, in the middle of the Midwestern winter, and at Burning Man, and it has held up fine, with only a little cosmetic damage to the Nomad (which is, without question, the most delicate part of the affair). No one EVER knows I have it, although obviously you couldn't check it through a concert where they search your bag without paying some attention to what you're doing.
That's it in a nutshell; until someone fills this gap with an all-in-one unit fit to plug mikes into and go, this is going to be the best you can do...and it's really, astonishingly good. I find that most of my recordings improve every time I listen to them on a better stereo, they are far and away better recordings than I can do justice to with my own playback equipment. Easy interviews, dope Podcasts in the field, concerts, ambient sound...you can figure out what this is good for better than I can!
Step 5: Justification (Technical)
The original machine for this job was the DAT and you'll still see it used. DATs can record at 44.1 and 48 kHz (16 bit stereo) standard, and various higher-end units established the standards such as 96, 88.2, and 192, typically in 24 bit. The DAT has recently been made obsolete, but all this means is that cheap, new-in-box closeout units are available. The media will not be dead for another half decade, minimum; DAT is workable as a solution, still.
DATs major limitations are the size (180 minutes, tops, at CD quality), and the noise, both mechanical from the rollers and electrical from the heads. This latter is a major problem, and the A/D preamps like the AD-20 were originally designed to get a higher quality of recording onto a DAT.
There are a couple options that replace DAT, which is why DAT is considered obsolete. The first was MiniDisk; originally a tiny CD-R with lossy compression, the latest HiMD format can record up to 90 minutes of 44.1 kHz 16 bit stereo, our old friend "CD quality". The later is CompactFlash, and the players that support this offer in some cases 24 bit, 96 kHz stereo, which is quite a bit better, on paper, than CD quality. Even better, CompactFlash is solid state, and will not make noise, like the DAT heads do, like the Minidisc assembly does, and like the Nomad's hard drive (which is LOUD and can be easily heard in a recording made using the Nomad's dinky onboard preamp).
Let us, then, attempt to assemble a system that gives us this 24/96 recording. Let us further assume that our goal is not to impress the numbers oriented, but rather to take a fine recording. Towards that end, we wish to actually capture 24 bits of signal, at 96kHz, over both channels.
Everything makes noise. If you are by a busy highway, and whisper, you will not be heard. Audio engineers say your whisper is below the 'noise floor' of the environment near that highway; the noise is louder than the signal. Everything below the noise floor is garbage; if you recorded the same signal again you'd get different noise. Furthermore, a stereo has a noise floor too, quite noticable on cheap speakers but many systems worth a few hundred have significant hiss when their gain is amped. Anything recorded below the noise floor of your stereo or headphones, you can't hear.
The one player which supports 24/96, the MAudio Microdrive, is known to be noisy enough that the noise floor is above the 16-bit mark. "bit depth" has to do with the granularity of the sample taken (think of an 8 bit sample as a Riemann sum of the waveform with 256 possible amplitudes and you're getting it); the additional 8 bits you get with a 24 bit stream relate to extremely small vibrations. If the noise floor is above the bit depth, you are recording noise. If the noise floor is above the 16th bit, the only difference between a 16 bit recording and a 24 bit one is the high-fidelity machine noise at the bottom.
The whole path from microphone to media, in other words, must be free of mechanical and electrical noise down to the 24th bit. This is possible. You will need condenser mikes of excellent quality, a pro phantom supply, and an A/D that can actually do the job. The CoreSound24/96 is the only unit, portable from the factory, that does the latter two, of which I am aware. If you have a digital signal path from the A/D to the media, the media can have moving parts; if the A/D is in the same enclosure as the media, moving parts are right out. The Nomad chokes on a 96kHz sample, so it's out of consideration from the beginning.
What of our 96 kHz? More samples, even at a 16bit technical resolution (you can toss the garbage third of your recording in a postedit), are a good thing for your sound quality. The dynamic range of the Microtrack is suspected to degrade at the 96kHz signal rate; may or may not be true; let's assume it isn't. Either way, it's too noisy to meet the standard; we want our noise to be recorded from the environment, not the machine!
The Microtrack has a port, however, for digital in. Therefore, by chaining a phat pair of microphones to a Coresound 24/96, to a Microtrack carrying a 6gb Microdrive, you would have something pretty nifty. You could, in fact, fit just around three hours of audio into such a system, assuming a supplemental battery for the Microdrive, which would be easy to rig. Your cost is a thousand for the Microdrive and CoreSound, at least five hundred for the mikes and 6 gb microdrive, and some peanuts for connecting cables and a battery.
But wait! You ain't done! Remember the noise floor? What';s the noise floor on your amp? What about your speakers? Looked into it recently? Many people claim not to be able to tell .mp3 from CD quality in the first place; some are just deaf, most have crappy speakers. For maybe another two grand, you could get the amplifier and headphones that would show you the difference between 24/96 and 16/44.1; if you want speakers, it's going to be a lot more, and you're going to want to give pretty serious thought to the acoustics of the space you install this in.
I love this system; I even covet it, to a degree. Can't afford it though, and sure can't afford to appreciate the difference it would make..and I took more than 6 gigabytes of recordings at Burning Man.
As for other, more stripped down systems...well, looks to me like you could replace the Nomad with an MAudio Microtrack and a 6gb Microdrive in my system. Cost you more, with less functionality, but you would have a product that is new and still supported by the company.
Perhaps more in the spirit of the Instructables community is to buy an old Nomad with a wonky thumbwheel and no batteries, rig a 5V power supply, and add a better control to replace the thumbwheel. Mount the circuit board on top of a half-terabyte 3 1/2" hard drive, build custom enclosure, and get jiggy with same. Nomads in this condition are 60 bucks, tops, and a few fly across eBay a week.