Noise floor
The constant hiss or hum sitting under everything you recorded. You only notice it in the pauses, until you boost the audio.
See it
What it is
Everything in the room that is not your voice, added together and sitting there at a constant level: the fridge, the HVAC, the laptop fan, traffic through the window, and the electrical self-noise of the mic and preamp. You measure it in dBFS by finding a pause and reading the level. A good spoken-word recording has a floor around -60 dBFS or lower; a phone in a kitchen might be -35 dBFS and there is no plugin that undoes that.
What actually matters is the gap between your voice and the floor (signal-to-noise ratio), not the floor's absolute number. You widen the gap at the source, not in post: get the mic closer, kill the fan, throw a duvet over the reflective surfaces, use a directional mic pointed away from the noise.
Gotcha: any upward gain move drags the floor up with the voice. A compressor with makeup gain, an EQ boost, a normalization pass that has to add gain: the hiss rises by exactly as much as the speech does. Turning a file down lowers the hiss too, and neither direction changes the ratio between them, which is why the volume knob is never the cleanup tool. And the floor only becomes obvious when it stops: cut to true digital silence and the hiss slams off, which sounds like a dropout. That is exactly why editors keep room tone on hand to patch the gaps.
Ask AI for it
Measure and report the noise floor of this recording: find a 1 to 2 second pause with no speech, report its RMS level in dBFS, then report the average RMS of the speech and the resulting signal-to-noise ratio in dB. Identify what the noise is (broadband hiss, 50/60 Hz mains hum, fan rumble, air conditioning) and say whether it is low enough to leave alone or needs cleanup before compression lifts it.