CD Quality Field Recording Rig





Introduction: CD Quality Field Recording Rig

Describes how to assemble a field recording system that is: battery powered, capable of six hours continuous record without recharge (and much more from the wall), CD quality (44.1 kHz 16 bit stereo), less than U$1000, and capable of being concealed in a handbag, backpack or jacket.

Step 1: Get Your Stuff: Nomad

In our world of excellent quality, tiny digital cameras and videocams, one would think there would be similar development in audio recording also, but that just isn't the case. While there are a few solid-state recording devices, they are expensive or large or both, and rely on compact flash, with its limited capacity.

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

Here we begin to have options, namely three. In order of price, they are:

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 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

You need microphones now, and then you're set to go. Binaural microphones are best for general purpose use, while cardoids are better for when you have a directional source, like a stage that you're fairly far away from. If you needed cardoids, you'd know it. Sound Professionals has good mikes as well as all the little cables and whatnot that you'll need (for this exact system, a 1/8" RCA stereo female to balanced XLR male and a TOSLINK male to RCA male optical cable); so do lots of people. The battery box can be made, if you know how; I don't, and this would make a good instructable. I opted for the less simple (but doubtless still homebrew-able) battery box with bass rolloff, for eliminating clip in high-bass situations. Dremeling a housing is easy and worth it, as it would be a pity to have random EM emissions fucking up your otherwise fully shielded system.

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

Pretty much set to go, here: attach mikes to power, power to A/D, A/D to Nomad, turn on Nomad, and record as per instructions. Updating the firmware of the Nomad is a good idea. You can tell an AD-20 is on because the optical port glows.

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 can figure out what this is good for better than I can!

Step 5: Justification (Technical)

The comments I've received on this Instructable have prompted me to add another section, for those curious as to why, exactly, the various other systems on the market were not considered for my purposes. Hopefully this will make the process more useful for those looking to do their own recording, many (even most) of whom will not settle on this exact rig.

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.



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same image in all the steps

The Gemini IKey USB audio recorder does the same for about $130 street price. The one I use is so simple it can only record. If you want to play back the files (mp3 or wav 16/44.1) you have to remove the thumb drive and play it on another device. I comes wit a stereo mike, RCA inputs for line sources and a headset jack for monitoring. I think a newer version than mine (about a year old) may have more features. I use the aux outs on a small mixer. This lets me use condenser mikes, etc.

Hi atman,nice set up. I am also just trying to set up a rig for recording while travelling: it must be very portable, long recording time, long power etc..even though I learned that the A/D of an HiMD should be superior I opted for an iriver H120 for it's onboard storage and drag+drop functionality. I also just bought SoundProfessionals SP-CMC4s and an SP Battery Box ( used, not yet arrived ) Can you please tell me, just how much does the AD-20 improove on the quality of your recordings? I also want to record 'ambience' and therefore need a system of very low 'self-noise' and I am wondering if I will need the AD-20 for that or if I can avoid the additional bulk and weight. and: from where did you get that cable adapter to connect your mics or battery box ( mini stereo ) to the 2 mono XLR of the AD-20? Or did you make it yourself? If so, could you tell me how to wire it?

If the iRiver has a digital input, the AD-20 will improve performance, as explained in the instructable and comments. If it does not, this device is not likely to be helpful to you. The cable adapter is from Sound Professionals.

For around the same money I'm using an Edirol R-1 ($440 street price) with a Sony stereo mic, plus a couple of large CF cards. The R-1 is a very sweet little unit. Among other things it has a lock feature so you can set it to record, turn on the lock, and throw it in your pack, and even if any buttons on the unit get pressed while it's in your pack, it just continues doing what it was set to do. It can also do digital out (optical or USB) so if you wanted to you could hook it up to an external storage device like the Nomad, but I haven't tried this. Next on my to-do list is to make an external D-Cell power supply, since the R-1's battery life is only around 2 hours. Nice thing about the R-1 is if steath is required, it's just one wire to a mic, that's it. Simple. And if stealth is not required, the unit has quite good built-in mics on board, and since it's solid state (no spinning hard disk noise) it is dead quiet. Plus it has 24-bit recording if you need it. And long duration as well (assuming an external power source). I can get 24 hours with MP3/192, which is pretty decent quality. I like CF cards because instead of having all my eggs in one basket (a large hard disk that could get stolen, lost, confiscated, etc.) the data can be put away safely after it is recorded. But SD cards would be even better. Actually to talk about dream audio recording setups, my dream setup would have some sort of reliable short-range wireless data capability so the recording could be done by one person while the storage was done by another person. Thanks for the article! Great to learn more about some of these devices.

Ooooh, the short-range wireless is genius. Bluetooth A2DP should make this trivial. You could even put the left and right mics on different accomplices and get really crazy with the stereo separation! I wonder if any cellphones have audio hardware that's a bit more capable than is required for a phone call. That'd be the ultimate in stealth, since the mic and bluetooth radio are already there. Quality is doubtful though. I can picture some sneaky mods to improve preamp / ADC quality without being externally detectable...

How do the Nomad Jukebox 1 and 2 stack up against version 3? They both seem to offer toslink digital in. Do they offer equal recording quality, or do they have some other problems?

Simpler and cheaper solution (on one hand): Buy a HiMD recorder, plug a portable mic straight into it. With a unit like the RH10, you can use the internal battery + an alkaline AA to keep recording for over 5 hours at 16-bit 44.1kHz LPCM (and over 10 hours @256kbps atrac3plus, which is more than sufficient for non-purist recording of any kind). The recorder and a mic (such as the earworn SP-TFB-2 binaurals that I use) will cost less than $450USD. Additional 1GB discs can be found for between $5-10USD. Has optical in and thus can be used with external A/D if so desired. The caveats: having to use SonicStage to upload your recordings (which, if you have more than a pea for a brain, isn't a problem); slow upload/download speeds (a restriction of the magneto-optical media used); no direct XLR inputs or Otherwise, the recorder fits in your pocket, doesn't require any additional external hardware at all for most portable recording situations, is cheaper than any other current solution available, and makes remarkably high-quality recordings for something that fits in your pocket and runs off one battery. And it outperforms the M-Audio recorder. For the budget-conscious, there is literally nothing else currently on the market that can compare.

I am really impressed with HiMD recorders as well-- even for very demandning applications like recording ambience in quiet locations. For me, quality starts with the preamps and pres in the HiMD recorders have exceptionally low noise perfromance-- low enough to allow one to use noise condenser mics with 12dBA self noise without the mic pre contributing noise. For recording ambience and soft sounds, the preamp's high gain of 75dB can provide bit depth saturation and effective resolution greater than recorders with 24 bit recording because these units often have 53dB gain or less. Its understandable that people would be sceptical that a <$200 recorder could have such quality, so I made "a hear it for yourself" test in which a pair of very low noise Rode NT1-A mics (5.5 dBA self noise) are first run through a Sound Devices 722 recorder and then through a ($70) Rolls PB-224 phantom power supply and into a Sony NH900 HiMD's mic input. The M-Audio Microtrack recorder is also included in the comparison. (4mb quicktime movie) For long duration recording, HiSP mode supports 7 hours and 50 minutes of ATRAC 3+ quality which, if saturations are kept high, is of surprisng quality. Rob Danelson

The biggest caveat, from my perspective, is that a 1 GB disk will simply not enable a six hour recording session, nor will a gumstick battery. The HiMD is another DAT killer; good for it. The optical in marks in its favor, but one needn't be a purist to ask for CD quality and get it; one might be planning to release the recording in CD format, or planning to extensively post-edit the sounds, perhaps as samples, in which case one wants as much bit depth as possible. There is no way you're going to get the kind of quality A/D conversion that a dedicated preamp A/D will give you, not with that minidisk spinning millimeters away. This is probably okay though, for applications under two hours. The truth is, you have a lot of options, in that department. DAT still has some juice in it; anyone want to bring it up? You can make a CD quality recording with DAT, still, to this day...if you don't mind it being under two hours.