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Reducing this by 5 dB yields a preamp EIN of -133 dBu, A-weighted. The difference between the microphone’s output noise of –112 dBu A-weighted and the preamp’s EIN of –133 dBu A-weighted is –21 dB so the preamp’s noise will not degrade the performance of the mic. "Selecting Mic Preamps" Download this note in PDF.
The green line represents the frequency response, the gain fader to the right is the same function as iTunes' preamp fader, and the orange line is phase. Hope this helps. permalink