Data storage

Written by Jonathan
Last update

1. What is the size of the recording after one night?

After one night, the raw data file of the recording (.h5 file) is around 70MB.


2. What's your policy in terms of data privacy?

Dreem follows GDPR rules. Please note that for your study, Dreem subjects' accounts will be created with dummy names, age, and gender. Only the principal investigator or authorized personnel will have access to the correspondence table that contains both the identity of the subjects and identifiers. Dreem won't have access to any personal data.
Upon request, data can be deleted at any time during the study. At the end of the study (or after a few months depending on the agreement), Dreem will delete all the recordings from its server.


3. How is data transferred and where is it stored?

Data is available in multiple formats, all of which are open and can be analyzed and/or processed with adequate tools. The unprocessed raw data is available as binary blobs. Once processed they are stored as HDF5 files and/or EDF.
Currently, recordings must go through our servers in order for them to be accessible. The storage pipeline is as follows: First, the recording is created and stored in the headband on its internal storage. Once the recording is over and the headband is plugged in and connected to WiFi, the recording is uploaded to our servers and deleted from the headband. The raw recordings are then accessed and processed by our internal services, making them available for download afterward.
The actual storage for these records is Amazon S3. For EU users, all our servers and storage capabilities are located in an AWS region located within the EU. Data access permissions are granted only to you and certain members of our team.


4. For how long can I hold data in the headband?

The headband can hold around 240 hours before overwriting the recorded data. That means you shall be able to recover all (or most of) the data, of 30 nights without WiFi (unuploaded data).


5. Can I upload the data to my phone and then synchronize them with the cloud after several days?

The headband upload data directly through Wifi with no transit through the App. Hence, you can not store data on your phone.


6. What format are the recordings in?

You can download several type of data under different formats as follow:
- Raw data encoded in binary blobs (.tar.gz). (Unfiltered)
- Raw data in h5 format. (Unfiltered)
EEG and 3D accelerometer data in EDF format. This is usually the preferred format for researchers wanting to import the file in their scoring software or for researchers using EEGlab on Matlab or a specific EEG toolbox on Python. The filtering procedure to transform an .h5 into a .edf is as follows: 1) An order 2 butterworth bandpass between 0.4 and 18Hz. 2) Three notches filter for 50Hz, 60Hz and 62.5 Hz of order 3
- Hypnogram in a time series format (.TXT). Sleep stages, which are determined by the sleep staging algorithm every 30s epochs, are listed chronologically in this file.
- Sleep metrics report in .CSV. It contains general information about the record (record number, start time, duration, channel quality) and sleep metrics (WASO, TST, sleep stage duration etc).


7. Is it possible to store the data on local servers?

The data is accessible on our external online "Dreem Portal", and you are encouraged to download and store it on your servers.