What file format, level, peak and noise-floor numbers does ACX state for audiobook submissions, and how do I check an audiobook chapter file against them?

ACX (2023 snapshot) states RMS-based spoken-word limits (-23 to -18 dB RMS, -3 dB peaks, -60 dB RMS noise floor), 192 kbps+ CBR 44.1 kHz MP3, uniform channel format (mono recommended, no joint stereo), and human narration only; it does not use LUFS or true peak. Curator qualifications: Pages and standards read 2026-10-22; no audio files measured or converted. Archived 2023 snapshot; the live page may differ (not re-read live). Measurement windowing for RMS is not defined on the page. Limitations: Pages and standards read 2026-10-22; no audio files measured or converted. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

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    {
      "url": "https://web.archive.org/web/20230925035211id_/https://www.acx.com/help/acx-audio-submission-requirements/201456300",
      "note": "ACX Audio Submission Requirements, Internet Archive id_ snapshot 20230925035211 (bytes equal producer pin)"
    }
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