Can you compare microphone preamps and A/D D/A converters using specs alone?
Yes!
But with some caveats.
One other factor is build quality. If the knobs feel terrible and stick etc, and it breaks a few weeks after you bought it, then specs are irrelevant. This is one big reason good stuff costs more than cheap stuff, even if they spec (and sound) identical.
As for specs, the only reason a comparison based on specs alone might fail is if the manufacturer fudges the data. Many years ago power amplifier makers took, um, let's say, "liberties" with the way they assessed maximum output power. If the amp could put out 100 watts for 1/10th of a second but no longer, they'd claim it as 100 watts. Eventually the US government stepped in and set laws for how output power must be specified. But there are no laws for the other specs.
Say for example one unit has a dynamic range of 110db and another has a range of 114db. Does the unit with 114db have better converters (assuming bit rates and sample rates were both the same)?
This is a perfect example of why you need to really understand the science behind the specs. Most companies spec dynamic range as the total span between the noise floor and the maximum output level before gross clipping. But other makers are more conservative and consider dynamic range from the noise floor to 0 VU (for a preamp or compressor etc). So on paper the latter might look worse than the former, even if it's really 10 dB better.
Then there's noise weighting. Most electronic gear has a response far beyond 20 KHz. This means there's ultrasonic noise at the output that is not audible. So it's reasonable for a preamp company to filter everything above 20 KHz when spec'ing the noise. But is it reasonable to use A Weighting too? Weighting reduces the lows and highs by a specific amount to emulate how our ears hear (Fletcher-Munson). If one company uses A Weighting and another does not, the two specs cannot be directly compared.
And if one unit has a mic preamp gain of 60db and another has a gain of 50db. Is the one with 60db a better preamp?
Not if 1) you don't need more than 50 dB of gain, and 2) the preamp with 60 dB gain has much higher distortion etc.
I hope it's clear that reading and comparing numbers alone is not enough to assess gear unless you truly understand what all the numbers mean and how they are often manipulated. But in the end, when all else is equal, numbers do indeed tell the entire story. If someone doesn't believe that, then they basically don't believe in science at all.
--Ethan
