A small apartment bedroom at night set up for recording, a window air conditioner above a desk with a laptop showing a waveform, headphones and a grey moving blanket on the wall
Voice Over Articles

Hear the Hum: What ACX’s -60 dB Noise Floor Actually Sounds Like

Sarah Robbins · September 27, 2026 · 4 min read

Every audiobook uploaded to ACX has to clear the same technical checks, and one of them trips up home narrators more than any other: the noise floor. ACX's rule is short. "Each file must have a noise floor no higher than -60dB RMS to avoid background noise distractions." What the rule doesn't tell you is what -60 dB actually sounds like, or how close your own room is to it.

So Voice Over Herald made it audible. Below is the same narration four times, mastered the same way, over four different amounts of room noise. Play one, then tap another while it runs.

ACX's own audio explainer series, fronted by a character called Alex the Audio Scientist, defines it as the "level of background noise in a recording, when no narration is taking place." In other words, it's what's left when you stop talking: the room tone in the pauses between sentences.

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