Equivalent Input Noise (EIN)

A rating of the overall noise performance of an amplifier (typically a microphone preamplifier). Basically, this is a measure of how much noise a mic preamp will add to a microphone’s signal. Measurements are normally made with a 150 Ohm resistor on the preamp to simulate the load a mic would present. The theoretical limit on EIN is -130.0 to -131.8 dBm (the thermal noise generated by the resistor). When comparing this spec, keep in mind that larger negative values are better (i.e. -124 is better than -118). But don’t place TOO much weight on this spec, most current EIN specs are infinitesimally small (can you REALLY hear the difference between -120 dBm and -122 dBm??)