BDF+ is a 24-bits version of EDF+. EDF+ is the populair medical time series storage fileformat.
EDF+ stores digital samples (mostly from an analog to digital converter) in two bytes, so the maximum
resolution is 16 bit. This is sufficient for most purposes. However, sometimes an ADC is used with
higher resolution. 22 bit ADC's are not uncommon these days. BDF+ is designed to store samples in three
bytes, giving it a resolution of 24 bit.
Like EDF+ is an extension of EDF, BDF+ is an extension to BDF. BDF is the 24-bits version of EDF used
by Biosemi, hence the name Biosemi Data Format. A description of the BDF fileformat can be found at the
website of Biosemi: http://www.biosemi.com/faq/file_format.htm
(Note that the author is not affiliated to Biosemi.)
The idea behind BDF+ is that EDF+ software can be easily modified to accept BDF+ because the headers
are the same, only the samplesize of the datapart increased from two to three bytes per sample.
BDF+ is compatibel with BDF. BDF+ files can be read and processed by older BDF software.
Note that BDF+ is not a competitor to EDF+. Please use EDF+ wherever possible. Only in those (rare) cases
where you need a higher resolution, consider using BDF+.
For the same reasons like it is better to use EDF+ instead of EDF.
EDF+ and BDF+ can:
- contain more patient- and other info in the header.
- contain annotations/events.
- be discontinuous (can store interrupted recordings).
- store the date in four digit format instead of two digits ("2008" instead of "08").
For a complete format description of BDF+, you need the EDF+ format description as well.
It can be found here: http://www.edfplus.info/specs/edfplus.html
Because the differences between EDF+ and BDF+ are small, only these differences will
be described here:
- The filename must end with ".bdf" or ".BDF" without the quotes.
- The version field must contain the following 8 octets: 0xff, 0x42, 0x49, 0x4f, 0x53, 0x45, 0x4d, 0x49.
- In case the recording is continuous (uninterrupted recording), the reserved field (44 octets) must start with the string "BDF+C" without the quotes.
In case the recording is not continuous (interrupted recording), the reserved field (44 octets) must start with the string "BDF+D" without the quotes.
The rest of this field must be filled with spaces (0x20).
- The label field of the BDF annotationchannel(s) (16 octets) must contain "BDF Annotations " without the quotes.
- The digital minimum field of the BDF annotationchannel(s) (8 octets) must contain "-8388608" without the quotes.
- The digital maximum field of the BDF annotationchannel(s) (8 octets) must contain "8388607 " without the quotes.
- Contrary to EDF+, there is no sizelimit for the datarecords.
- Any datarecord duration value greater than 0 is allowed, like 1234, 1.4567, 0.0001, etc.
- The 24-bit data samples are two's complement and little endian:
+-----------------------+-----------------------+-----------------------+
LSB |01|02|03|04|05|06|07|08|09|10|11|12|13|14|15|16|17|18|19|20|21|22|23|24| MSB
+-----------------------+-----------------------+-----------------------+
| byte 1 | byte 2 | byte 3 |
| |
|<-------------------------- one sample ------------------------------->|
- In BDF+ the patientfield is divided in five subfields:
- patientcode
- sex
- birthdate
- patientname
- additional info
- In BDF+ the recordingfield is divided in five subfields:
- the text "Startdate" followed by the startdate itself
- administrationcode
- a code specifying the responsible investigator or technician
- a code specifying the used equipment
- additional info
For details about how to write these subfields, read the EDF+ specification.
- In BDF+ the reserved field (44 octets) starts with the string "BDF+C" without the quotes or
"BDF+D" without the quotes.
- A BDF+ file contains at least one signal which has the label "BDF Annotations ". No other signals
will have this label except for annotations.
The first annotations-signal must contain a timestamp for every datarecord as described in the
EDF+ format description. For details, read the EDF+ specification.
EDFbrowser supports BDF+. It has also a built-in BDF+ format checker which makes it easy to check your files
for possible errors.
EDFbrowser has a BDF+ to EDF+ converter.
EDFbrowser is available for download here.
EDFlib is a programming library for C/C++ for reading and writing EDF, EDF+, BDF and BDF+ files.
EDFlib is available for download here.