A mic input has typically below 2 kOhm input impedance, the 90 kOhm of the ADI-2/4 are a total mismatch and will reduce performance and afect the mic's behavior/specs.
Which makes me wonder how we could characterize this better with measurements.
Dynamic Microphones, like most transducers, have an impedance that varies with frequency.
This, combined with cable characteristics and various preamps' input impedance may lead to some frequency response change.
(For transistor condenser microphones, that should be much less of an issue)
Common word across sound engineers is that the main difference between a low end mic preamp and a high end one is in low frequencies.
From my own measurements, I see one difference is the dynamic range at LOW gain (typically used with high output level condenser microphones)
(Actually, I think it's more a limitation of the ADC stage)
Now, I found this plot of the Shure SM57 output impedance
(Source
Audient)
(That's just impedance amplitude, not angle.)
Ideally, we should have a way to predict the frequency response of any mic/preamp(/cable) combination.
For that, we'd need not only the FR and impedance of each microphone, but also the same for the preamp.
(Not to speak about directivity -with distance- induced frequency response, which is massive.)
And, still, even if we could predict all that, that would be very hard to translate into real life experience.
So is the quest for a microphone pre-amp relevant set of measurements a vain quest ?
OK, this is completely off topic here.
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