# Why can one spoken-word file meet ACX, Apple Podcasts and AES TD1008 numbers differently, and what must I record when I claim a file 'meets spec'?

- id: art_01M5MRK2YFBAW74XAM7J2CK8DX
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T13 · tags: none
- updated: 2026-10-23T16:13:04.300Z
- url: https://veyrul.com/articles/art_01M5MRK2YFBAW74XAM7J2CK8DX

Spoken-word targets use incompatible bases: ACX (audiobooks) sets an RMS window of -23 to -18 dB, -3 dB peaks and a -60 dB noise floor; Apple Podcasts measures LKFS and true peak per BS.1770; AES TD1008 recommends -18 LUFS dialogue-integrated loudness with -1 dBTP at the codec input (lower bit rates overshoot more). A pass on one basis does not imply a pass on another; reports should name the measure and whether peaks are sample or true peak.

Spoken-word targets use incompatible bases: ACX (audiobooks) sets an RMS window of -23 to -18 dB, -3 dB peaks and a -60 dB noise floor; Apple Podcasts measures LKFS and true peak per BS.1770; AES TD1008 recommends -18 LUFS dialogue-integrated loudness with -1 dBTP at the codec input (lower bit rates overshoot more). A pass on one basis does not imply a pass on another; reports should name the measure and whether peaks are sample or true peak.

Curator qualifications: Zero-fetch review 2026-10-22 against held readbacks; no audio measured. ACX page is an archived snapshot.

Limitations: Zero-fetch review 2026-10-22 against held readbacks; no audio measured.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://web.archive.org/web/20230925035211id_/https://www.acx.com/help/acx-audio-submission-requirements/201456300",
      "note": "ACX submission requirements (snapshot 2023-09-25); Apple Podcasts audio requirements, Audio levels; AES TD1008 (2021-09-24) p.2, p.8, p.15"
    },
    {
      "url": "https://podcasters.apple.com/support/893-audio-requirements",
      "note": "ACX submission requirements (snapshot 2023-09-25); Apple Podcasts audio requirements, Audio levels; AES TD1008 (2021-09-24) p.2, p.8, p.15"
    },
    {
      "url": "https://web.archive.org/web/20240714082802id_/https://aes2.org/wp-content/uploads/2024/01/20210924_TD1008_v3.13.pdf",
      "note": "ACX submission requirements (snapshot 2023-09-25); Apple Podcasts audio requirements, Audio levels; AES TD1008 (2021-09-24) p.2, p.8, p.15"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Spoken-word targets use incompatible bases: ACX (audiobooks) sets an RMS window of -23 to -18 dB, -3 dB peaks and a -60 dB noise floor; Apple Podcasts measures LKFS and true peak per BS.1770; AES TD1008 recommends -18 LUFS dialogue-integrated loudness with -1 dBTP at the codec input (lower bit rates overshoot more). A pass on one basis does not imply a pass on another; reports should name the measure and whether peaks are sample or true peak. · locator: ACX submission requirements (snapshot 2023-09-25); Apple Podcasts audio requirements, Audio levels; AES TD1008 (2021-09-24) p.2, p.8, p.15 · source: https://web.archive.org/web/20230925035211id_/https://www.acx.com/help/acx-audio-submission-requirements/201456300

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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