EDF format description

EDF data format.

The EDF format is a simple and flexible format for the storage and exchange of multichannel biological signals. The data consists of a header record and then all of the data records from the beginning to the end of the recording. The header consists of two records.

The first record of 256 bytes specifies the version of the data, patient information, time information of the record, the number of data records and the number of signals in each data record.
Then there follows a record whose length depends on the number of signals in the recording. For every channel 256 bytes are needed. This record contains information about the type of signal, amplitude, calibration and the number of samples in the data record.

Header Record (first part)

The first part of the header record is build-up as follow.

number of bytes	field type	description	format
8	ascii	Version of the data format (for EDF is that 0)	-
80	ascii	Local Patient identification	-
80	ascii	Local recording identification	-
8	ascii	Start date of the recording	dd.mm.yy
8	ascii	Start time of the recording	hh.mm.ss
8	ascii	Number of bytes for the header record	-
44	ascii	Reserved	-
8	ascii	Number of data records (-1 if it is unknown)	-
8	ascii	recording time of the datarecord	in seconds
4	ascii	number of signals in a data record (ns)	-
The first part of the header contains 256 bytes

Header Record (second part)

The second part of the header record is build-up as follow.

number of bytes	field type	description	format
ns * 16	ascii	Signal lable. (e.g. EEG FpzCz, Body temp or EDF Annotations)	-
ns * 80	ascii	Transductor type ( e.g. AgAgCi electrode)	-
ns * 8	ascii	Physical dimention (e.g. µV or degreeC)	-
ns * 8	ascii	Physical minimum (e.g. -500 or 34)	-
ns * 8	ascii	Physical maximum (e.g. 500 or 40)	-
ns * 8	ascii	Digital minimum (e.g. -2048)	-
ns * 8	ascii	Digital maximum (e.g. 2047)	-
ns * 80	ascii	Prefiltering (e.g. HP:0.1Hz LP:75Hz)	-
ns * 8	ascii	Number of samples (nr) in each data record	-
ns *32	ascii	reserved.	-
The second part of the header contains (ns) * 256 bytes

The data record.

A data record consists of the data samples of each channel where all data samples of channel 1 consecutive be saved. Then comes channel 2 ... until all channels are stored. This record will be followed by another new record of the specified data recording time.

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