Export format differences

CSV:

CSV is an interoperable file format for storing tabular data in plain text. One file is 
provided for every device signal. Supported for all Bitbrain devices. We provide two 
output formats with varying levels of detail (Lite and Full). 

EDF:

EDF is a standardized file format designed for storing biological signals. One file is 
provided for every device. Supported for Bitbrain devices containing EEG signals. We 
refer to “EDF” through the software and this document for simplicity, note however that 
we specifically provide the EDF+ format.

Main differences:

• Resolution and filtering: EDF represents the signal values in 2 bytes (16 bits), which does not allow to store the EEG and PPG signals as the full range of the amplifier ADC is 24 
  bits. Thus, EEG and PPG signals are high pass filtered (0.1 Hz, 2nd order Butterworth 
  filter) when exported to EDF format. CSV formats (CSV-Lite, CSV-Full) export the full-band 
  signals.
• Lost samples adjust: Some signal samples might be lost due to the wireless nature of the 
  communication. In EDF and CSV-Full, the exported signals are expanded with nan values 
  in case of lost samples. In CSV-Lite, additional information is provided such a sequence 
  number (counter) to detect these cases.
• Multi-device adjust:  In simultaneous multi-device recordings, the devices might start the 
  recording with a slight difference (even when they are commanded at the same time). In 
  EDF and CSV-Full, we provide a common t0 for all signals, and expand the signals with 
  initial nan values so that the initial sample corresponds to the same time point. In CSV
  Lite, we simply provide the initial timestamp (t0) for each device signals, which might be 
  different.  

output data formats properties	EDF	CSV-Full	CSV-Lite
Supported devices	EEG devices (Ring or  Versatile Bio not  supported)	All	All
Full-band	No, EEG and PPG are  high prefiltered (0.1  Hz)	Yes	Yes
Lost samples adjust	Yes	Yes	No
Multi-device adjust	Yes	Yes	No
Supported in SennsLite	Yes	Yes	Yes
Supported in SennsLab	No	Yes	Yes

EDF Format:

An EDF file for every recorded device is provided, thus containing all its signals that operate at 
different sampling rates. 

Channel	Description
<signal_id><i> * In case of EEG signals, we provide  the position: <signal_id><loc>	Values of signal  and channel i (from 1 to N). EEG and PPG signals are high pass filtered (0.1 Hz, 2nd order Butterworth filter) and clipped to (-3000, 3000) uV.
mask_<signal_id>	Mask of boolean values (0 or 1) for each signal that  indicates whether samples were lost and should be  interpreted as missing values (nan).  Note we include a mask channel because nan values  cannot be represented in EDF format.  A sample j was lost in signal eeg when mask_eeg[j] is 1.

Header of the EDF file:

The header of the EDF file fills the following fields: 

• Start date and start time (note these fields provide a resolution of seconds; for a higher 
  time resolution access the UTC timestamps provided in the JSON file – metadata).
• Patient code
• Equipment (device type)

CSV Format:

We provide a CSV file for every recorded signal. 
The first line contains a header with the name of the columns.

The CSV file contains the following columns: 

Column	Full/Lite	Description
ch<i> * In case of EEG signals, the position is added: ch<i>-<loc>	Full/Lite	Values of channel i (from 1 to N).
sequenceNumber	Lite	Sequence number (counter) is incremented by 1 every block.
timestampReception	Lite	Reception timestamp (high res., us) per block, might be null if lost online.
timestamp	Lite	Corrected timestamp (high res., us), using the t0 computation.

Events:

The events registered with SennsLite during the recording are exported to CSV files. 
We provide a CSV file for every event type. 
The first line contains a header with the name of the columns.

The CSV file contains the following columns: 

Column	Description
timestamp	Timestamp (high res., us) when the event occurred.
value<i>	Value/s of the event.  Note that one event might have several values. For instance, one event type “quality” is provided for every device that provides the signal quality of every channel.