I'd like to see that, too- especially if it could be held to something resembling solid technical grounds, and not religion... I haven't, yet, but if I do I'll let you know.
So what the hell- let's start one here. What can go wrong? (;-)
I personally don't pay much attention to distortion specs any more. Very few vendors really measure them, and if they do, it's not clear under what circumstances... Many tube and solid-state preamps these days have a knob on the front labeled "warmth", and it really ought to be labeled "throw our advertised distortion figures out the window". I'm kind of a throwback, I guess- it bothers me a little bit that distortion is now considered a big selling point, and called "color" (;-). Well, when in Rome, be a Roman candle, I guess. Some distortion is good, and is called color, and damned if I can tell how they can square that big ol' "warmth" knob with the ".0000003% THD" or whatever spec they publish... So I ignore them. I probably couldn't hear it anyway, as old as my ears are getting.
Noise, on the other hand, is an extremely annoying thing under any circumstances: I *can* hear that, and I can't ignore it- now or ever. There are two flavors to worry about. There's EMI/environmental hash, and self-noise (thermal noise from the resistors in the input stage and from the active devices that follow them). You can't do anything about the thermal noise, unless you flood the control room with liquid nitrogen. Good for keeping the beer cold, but it's *hell* on the tape-ops (;-). Ultimately, the EIN is simply a function of the circuit topology and the ambient temperature. It's generally a very pinkish, broadband, moderately inoffensive thing to have as your noise floor.
The CMRR spec numbers, on the other hand, give you an idea about what sort of behavior a preamp will exhibit in a real-world setup with a mic plugged in, with all that EMI hash floating around the room. My experience over the years has been that a poor CMRR will lead to all manner of unpleasantness (excessive susceptibility to ground loop noise, CRT noise, power supply induction noise, and just flat-out *jit*), and that if the CMRR is too low, the EIN specs are rendered completely moot. Why? As soon as you plug a mic cable in and turn the monitors up, the common mode crud will absolutely swamp the thermal noise of the preamp. You'll never be able to hear it for the hum, crackle, buzz, and crud. At that point the EIN truly *is* a flea on the back of the elephant! Common-mode EMI noise is _never_ inoffensive: it is almost always pitched, and as such it "sticks up" above a pinkish noise floor. The human brain zooms right in on pitched artifacts.
Cool EIN specs (big negative numbers) are great, of course- but if you can't ever get there because all the electromagnetic crud in the room is stomping on even your best starquad mic cable and crawling into the signal path, you're well and truly screwed (IMHO, of course). I record a lot of acoustic music, and the noise floor (and the _character_ of the noise floor) is of great importance to me. Your mileage may vary...
The bottom line for me is that the Behringer box in question specs out *much* worse than a basic Mackie preamp from their cheapest, most entry-level board. Shoot, maybe it actually sounds like tits on a Ritz in practice, but I can't see how. It seems to me to be sort of sad to fork over nearly the same price as a small Mackie mixer for a 2-channel standalone preamp that has a very good chance to be much, much noisier, without listening to it _very_ carefully first: thus, my "caveat emptor". I believe, based on the specs, that this should not require anything resembling golden ears to hear the difference- especially if there's a CRT in the room!
Of course, since I'm the guy who shot my mouth off about it, I should hike over to Guitar Satan and try to talk them into letting me A/B this box with a little Mackie: two TLM103s, two 25-foot mic cables, two stands, and a pair of nice headphones. I'm intrigued enough about it to want to find out for myself.
Normally, 3-4dB in the noise floor would be damned near impossible to discern. -129dBu versus -134dBu EIN would have you straining hard to hear any difference at all, unless there was a basic difference in the *character* of the noise itself (a different frequency distribution between the two, or perhaps popcorn-dominated shot/impulse noise versus pink/white broadband). It'd be a right bitch to pick out 4dB in a blind test, so you're right. That's not a showstopper, and I probably should have left it out of my post altogether.
On the other hand, I absolutely do believe a 50dB difference in CMRR would stand out like a sore thumb once a mic was plugged in. If there's one flourescent light on in the room, you'll hear it: it should absolutely dominate the noise floor. It'd blow my mind if that box could achieve anywhere _close_ to its specified S/N when used in a room with a computer or a flourescent light in it.
That's my take, anyhoo. Most of it is pretty damned hard to hear- except anything that lets EMI in. Whaddaya think?
[Edited by skippy on 12-09-2000 at 17:49]
