It's always irked me a bit that @purr1n kept referecing levels in the 30dBA range as a very quiet ambient level, about the best you can normally get to. I did some tests in the past and when he repeated the same thing again in a new thread I remembered it. I think 30dbA is louder than a bedroom should be at night. One quick test I did was to set white noise at 50dBA on my desktop monitor speakers for a digital full scale signal in Audacity.* Then I normalized the levels to quieter levels. At 30dBA it was still pretty loud and I wouldn't want my bedroom to be this loud at night. Subjectively the 20dBA white noise was still louder than ambient here, at least at night. 10dBA is pretty darn quiet and at 0dBA it got hard to hear, especially over my monitor's PSU, the transformer hum in the amp I have on my desk, etc. When it started drizzling it was definitely much quieter than ambient. If I heard something at -10dBA I can't say it wasn't placebo without a blind test. Pink noise could be a better test that's worth trying, but ambient levels aren't continuous like that. There's stuff that makes a noise periodically that I can hear here, as mentioned in the other thread. The fridge downstairs keeps cycling on and off, as does the oil heating. Sometimes a car, a train, a plane. I don't live in such a rural area, either. Maybe I'm underestimating how loud large urban areas in the US or Asia are. Maybe someone else could try what I did and report back. *This will only be as good as your volume calibration - I used my UMIK-1 calibrated with @sorrodje's mic calibrator gadget a while ago. Back then I measured my headphones with a known output level, so I still have a reference - this way I can be reasonably sure it hasn't drifted much. Measuring speaker drivers the 2.83Vrms sensitivities I get are very close to what they should be, so I'll just have to assume it's accurate.