Originally Posted by didier.brest
They are flat ! All preamp manufacturers claim so. And indeed they are, except when one is out of its specifications.
The attached picture this is a screenshot from a shoot-out of a Fearn VT-2 and the preamps of an RME Fireface. They are both fed by the same mic pair (Beyer M 130) through an active splitter. The splitter has no gain and the mics are ribbons, which required maximum gain from the Fearn. The white and red spectrum lines from both tracks superposed near perfectly.
How can different pres exude different tonal qualities if they are tuned to have an identical frequency response?
What about this from Mackie-
1. A mic preamp should be able to protect itself from destructive external forces.
2. A mic preamp should not be prone to Radio Frequency Interference (RFI).
3. A mic preamp's response should not vary with different mic cable impedance loads.
4. A mic preamp should be accurate, sound good, and have very low noise and wide bandwidth at any gain level.
Many high-end outboard mic preamps achieve Goals 3 & 4, but lack protection and good RFI shielding. Conventional mixer preamps often meet Goals 1 and 2 at the expense of good sound.
A microphone's frequency response (and thus how it sounds) is a function of the load presented to it. That load is the impedance characteristic of the mic preamp it's connected to. If a mic preamp isn't designed right, it will actually sound different depending on the impedance of the microphone and the cable load.
With mic preamps, spoken-word tests and simple vocal recording often reveal a lot about the tonal signature of a circuit, and in a comparison test with one of my own relatively transparent-sounding preamps, the Pre 73 came across as having a very obvious character. It exhibits a strong and confident-sounding mid-range, very smooth highs and a generally ‘rounded’, slightly compressed-sounding tonality, that I found reminiscent of some tube mics and tube preamps. The Focusrite ISA 110 that I reviewed a few months ago had something of a similar tonal leaning, which I attribute to the use of transformers in the audio path, although much depends on the characteristics of the particular transformer employed and the circuitry that surrounds it.