Wow, even my brain is gonna explode from reading all of this. Greetings to all I haven't seen in a long time.
Going to give this one a cursory glance, don't have time to respond to every detail of the very fine discussion here.... but....
First, I'd be inclined to believe that there will simply be inherent differences in coloration attributable purely to different impedances between the output of a preamp at line level vs. the pure mic level output.
Second, as someone already said here, (sorry, too lazy to quote, so I'm gonna paraphrase) using a preamp will in most cases improve signal to noise ratio at the A/D. The quieter the material, the worse the signal to noise ratio. Noise being not just self noise from the mic and analog stage in the A/D, but also quantization noise from the A/D process.
Third thought, the best way to prevent any further noise from being added to the signal and still amplify the signal is to use bit shifting (e.g. some software... I think samplitude has a 2x volume function). Any sample value multiplied by exactly 2 will not generate a mantissa, and therefore, will not create additional noise. Amplification through bit shifting would be the only way to preserve the effect of dither and noise shaping once applied. Of course, in using this method, how close you can get to 0dBFS would depend on how close your loudest peak is to -6.02dBFS.
Fourth, I usually consider it simply like this. You really only have about 25dB extra headroom with the AD2K over the best 16 bit A/D. So -48dBFS is only in theory the same as 16bit at 0dBFS in terms of S/N ratio. In practice, it's probably closer to -24dBFS being about the same. Granted, when comparing differences down to this level, you'd also have to consider the differences in color of *all* frequences over the dynamic range for any given analog stage. I believe most specs center their S/N ratios, etc... around a 1kHz tone. As such, every analog component's self noise will have it's own unique FFT. The degree to which the noise signature with a preamp or without a preamp is complementary to the live source is purely up to the listener. In other words, the differences in self noise will impart a coloration to low level sounds. It is possible that cumulative (i.e. greater than the loudest noise, as John Siau puts it) noise dithers the sound better to your ear one way over another for your recording, much in the same way that white noise dither would sound different than "pinker" noise.
Bottom line, practically, I'd say, if you were willing to carry a Benchmark AD2402-96 to a show, you should be willing to carry a Grace Lunatec V3 to the show instead, and kill two birds with one stone.
I still love that V2->AD2402-96 combo, and for anyone curious, for 2 track live recordings (as infrequently as I do them these days), I still use the DAARWIN-24 Sony picturebook with the VXPocket, Win2K, and that Pre/AD combo. The combo continues to do exactly what it was designed to do 8 years ago, no reason to mess with a good thing. A solid state disk sure would be nice though. ;-) For the multitrack Hot Tuna shows, well, that's a whole other ball o' wax. Gotta love the Alesis HD24-XR for that.
(no, I don't read this board regularly at all.... too busy coding stock trading formulas these days. ;-)
jerryfreak roped me in on this thread. Somewhere along the line I also created two ID's here as well. And so it goes...)
Cheers, and keep up the quality discussion. Mmmmmmmmmmmmmore bits please.
Dan Heend
High Fidelity Microsystems
HFM Studios
www.hottunatunes.com