How offline transcription works
Brain Dump transcribes your voice to text entirely on your iPhone. No internet. No upload. No server. It works in Airplane Mode.
The data flow
- 1. You speak. Brain Dump captures audio through the iPhone microphone.
- 2. On-device processing. Apple's Neural Engine (the same chip that runs Face ID) converts audio to text using on-device speech recognition models. The audio stays on your phone.
- 3. Markdown file saved. The transcribed text is written to a
.mdfile in your Brain Dump folder in iCloud Drive (local copy). - 4. iCloud sync (when online). When you reconnect to the internet, the Markdown file syncs to your other devices via iCloud. The audio is never sent. Only the text file syncs.
Microphone → Neural Engine (on-device) → .md file (local) → iCloud sync (text only)
Audio never leaves your iPhone. No server involved during capture.
What works offline
| Feature | Offline | Requires internet |
|---|---|---|
| Voice capture | Yes | N/A |
| On-device transcription | Yes | N/A |
| Markdown file saving (local) | Yes | N/A |
| Siri phrase activation | Yes | N/A |
| Custom dictionary | Yes | N/A |
| Voice Activity Detection | Yes | N/A |
| iCloud sync | N/A | Yes (syncs when reconnected) |
| AI rewrite / summary | N/A | Yes (server-side AI) |
| App updates | N/A | Yes |
Supported devices
Brain Dump does not use Apple's dictation for transcription. It bundles its own speech-to-text engine, a whisper.cpp build that ships inside the app, so transcription runs locally on any device that runs the app.
- iPhone and iPad running iOS 17 or later
- Mac running macOS 14 or later
There is no Neural Engine requirement and no server fallback for transcription. Every supported device gets the same default model and the same list to choose from. Older hardware transcribes more slowly, because the work is real computation happening on your device, but it does not send the audio anywhere.
Supported languages
The bundled engine is multilingual. The exact language list depends on the speech model the app ships with, so check Settings on your own device for what is available in your build rather than trusting a list on this page.
Some languages may need to be downloaded before offline use. Go to Settings → General → Keyboard → Dictation Languages to manage offline language packs.
Verify it yourself
The simplest privacy test:
- 1. Turn on Airplane Mode
- 2. Open Brain Dump and record a voice note
- 3. Watch the text appear instantly
If it transcribes without internet, no data is leaving your phone.
Limitations
- Accuracy. On-device models are slightly less accurate than cloud models for uncommon words and heavy accents. The custom dictionary helps with names and jargon.
- First-time setup. Some languages require downloading an on-device model (one-time, requires internet).
- AI features need internet. Rewrite, summary, and action-item extraction are server-side features.
- iCloud sync needs internet. Files save locally and sync when you reconnect.
Questions
Does Brain Dump work in Airplane Mode?
Yes. Voice capture and on-device transcription work in Airplane Mode. Your note saves locally and syncs to iCloud when you reconnect.
Is offline transcription as accurate as cloud?
Very close. Apple's on-device models handle everyday speech well. For specialized vocabulary, use the custom dictionary. Cloud models may have a slight edge with unusual terms.
Does any audio get uploaded later?
No. Audio is processed on-device and discarded after transcription. Only the Markdown text file syncs via iCloud. The audio is never sent anywhere.
Can I use Brain Dump on a flight?
Yes. That's one of the most common use cases. Airplane Mode transcription means you can journal, capture ideas, or debrief meetings at 30,000 feet.