Understanding Microphone Noise vs Preamp EIN
In every audio recording chain, there are two separate sources of electrical hiss:
- Microphone Self-Noise: Caused by random brownian motion of air molecules striking the diaphragm and thermal noise in internal JFET impedance converters. Rated in equivalent acoustic dBA SPL.
- Preamp Equivalent Input Noise (EIN): Johnson-Nyquist thermal noise generated by the input transistors and resistors of your audio interface preamp. Rated in dBu (typically -128 dBu at 150Ω).
The Great "Cloudlifter" Myth Debunked
With high-sensitivity condenser microphones (30 to 50 mV/Pa), the microphone's self-noise is already amplified to approximately -110 to -115 dBu. Because a quality interface preamp has an EIN of -128.5 dBu, the preamp noise floor is over 13 dB quieter than the microphone itself! Adding an inline booster preamp (like a Cloudlifter or FetHead) to a condenser microphone achieves zero improvement in signal-to-noise ratio and merely adds extra distortion stages.
When an Inline Preamp IS Necessary
An inline booster is beneficial ONLY when using an ultra-low-output dynamic or ribbon mic (like the Shure SM7B at 1.1 mV/Pa) into an old or budget audio interface whose preamps become noisy or run out of clean gain above +55 dB.