Quick Reference
| Parameter | Requirement | Notes |
|---|---|---|
| RMS level | -23 to -18 dBFS | Same working range as ACX, consistent across all files |
| Integrated loudness | Approx. -20 LUFS | Where a spoken-word master in the RMS range typically lands |
| Max peak | -3.0 dBTP | Measured as oversampled true peak, hard requirement |
| Noise floor | -60 dBFS or lower | Holds in every silence, not just the head of the file |
| Sample rate | 44.1 or 48 kHz | Required |
| Bit depth | 16-bit minimum | 24-bit masters accepted |
| File format | WAV or FLAC | Lossless delivery, unlike ACX's MP3 requirement |
| Channel format | Mono preferred | Stereo accepted, mono recommended for narration |
How Storytel Delivery Differs From ACX
Same levels, lossless files
The level targets mirror the ACX working range: -23 to -18 dBFS RMS, -3 dB peak, -60 dBFS noise floor. The delivery format does not: Storytel takes WAV or FLAC, so you ship the master before MP3 encoding. That removes the encoder-raises-peaks problem that catches ACX submissions, but it also means your QC pass runs on a different file than the one you send to ACX.
Mono by recommendation
Storytel accepts stereo but recommends mono for narration. For single-voice audiobooks mono is the technically better delivery: half the data, no channel-balance risk, identical listening result. Keep stereo for productions that actually use the stereo field.
Consistency across the audiobook
Like every audiobook platform, Storytel evaluates the title as a set. Chapters recorded weeks apart need the same RMS level, the same noise floor character and the same channel format. A per-file pass with per-set consistency is what keeps a 40-file delivery from bouncing on file 37.
Distribution Context
Storytel is subscription-based and strong in Europe, the Nordics and emerging markets, which makes it a common second delivery target after ACX for wide-distribution titles. If your master passes ACX levels, the additional work for Storytel is packaging (lossless, mono) rather than re-leveling.
FAQ
Can I reuse my ACX master for Storytel?
Mostly, with one important difference: the file format. Storytel takes lossless WAV or FLAC while ACX requires encoded MP3. Deliver the pre-encode master to Storytel and the encoded MP3 to ACX. The level targets (RMS -23 to -18 dBFS, -3 dB peak, -60 dBFS noise floor) line up, so one leveling pass covers both.
Does Storytel reject files automatically like ACX?
Storytel's intake is less automated than ACX but the published requirements are the review baseline. Files outside the level or format requirements come back for redelivery, which on a 40-file audiobook costs more time than checking before upload.
Why deliver mono when stereo is accepted?
Single-narrator audiobooks carry no stereo information, so a stereo delivery doubles file size for identical content and introduces the risk of channel-balance issues. Storytel recommends mono for narration; stereo makes sense only for productions with real spatial content like multi-voice drama or music beds.
Is the -3 dB peak sample peak or true peak?
Treat it as true peak. Measuring the oversampled true peak (dBTP) is the stricter reading, so a file that passes at -3.0 dBTP also passes any sample-peak check. Since Storytel takes lossless files there is no encoder to raise peaks after your QC pass, but the safe measurement practice stays the same.
How does the noise floor requirement compare to ACX?
It is the same number: -60 dBFS or lower, held in every silence throughout the file. Room tone, breath gaps and pauses between sentences all count. A recording chain that passes the ACX noise floor check passes Storytel's too.