EDFlib is a programming library for C/C++ for reading and writing EDF+ and BDF+ files. It also reads "old style" EDF and BDF files. EDF means European Data Format. BDF is the 24-bits version of EDF.
The library consists of only two files: edflib.h and edflib.c.
In order to use EDFlib, copy these two files to your project.
Include the file edflib.h in every source file from where you want to access the library.
Don't forget to tell your compiler that it must compile and link edflib.c (add it to
your makefile or buildscript). edflib.c needs to be compiled with the options
-D_LARGEFILE64_SOURCE -D_LARGEFILE_SOURCE.
For example:
gcc -Wall -Wextra -Wshadow -Wformat-nonliteral -Wformat-security -D_LARGEFILE64_SOURCE -D_LARGEFILE_SOURCE test_edflib.c edflib.c -lm -o test_edflib
Compilation has been tested using GCC on Linux, Mingw-w64 on Windows, and LLVM GCC on OS X (Yosemite).
To understand how to use the library, read the comments in edflib.h.
To build the examples: make
Each "generator" example creates an EDF+ or BDF+ file with sample signals.
test_generator shows how to use most of the functions provided by the library and generates an
EDF+ or BDF+ testfile with several sample signals.
sine_generator creates a BDF+ file containing the signal "sine", a 1 Hz sinoidal waveform with a
sample frequency of 2048 Hz.
sweep_generator creates a linear or logarithmic sweep through a range of frequencies in EDF+ or
BDF+ format.
Use EDFbrowser to view these files: http://www.teuniz.net/edfbrowser/
test_edflib <filename> <signalnumber> will print the properties of the EDF/BDF header, the
annotations, and the values of 200 samples of the chosen signal. For example, running
test_generator will produce the file test_generator.edf. Running test_edflib test_generator.edf 6
will show the header and first 200 samples of the "noise" signal:
75 6 27 77 37 30 35 96 62 69 34 15 51 56 69 68 80 45 ...
In EDF, the sensitivity (e.g. uV/bit) and offset are stored using four parameters: digital maximum and minimum, and physical maximum and minimum. Here, digital means the raw data coming from a sensor or ADC. Physical means the units like uV. The sensitivity in units/bit is calculated as follows:
units per bit = (physical max - physical min) / (digital max - digital min)
The digital offset is calculated as follows:
offset = (physical max / units per bit) - digital max
For a better explanation about the relation between digital data and physical data, read the document "Coding Schemes Used with Data Converters" (PDF):
http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=sbaa042
An EDF file usually contains multiple so-called datarecords. One datarecord usually has a duration of one second (this is the default but it is not mandatory!). In that case a file with a duration of five minutes contains 300 datarecords. The duration of a datarecord can be freely choosen but, if possible, use values from 0.1 to 1 second for easier handling. Just make sure that the total size of one datarecord, expressed in bytes, does not exceed 10MByte (15MBytes for BDF(+)).
The RECOMMENDATION of a maximum datarecordsize of 61440 bytes in the EDF and EDF+ specification was usefull in the time people were still using DOS as their main operating system. Using DOS and fast (near) pointers (16-bit pointers), the maximum allocatable block of memory was 64KByte. This is not a concern anymore so the maximum datarecord size now is limited to 10MByte for EDF(+) and 15MByte for BDF(+). This helps to accommodate for higher samplingrates used by modern Analog to Digital Converters.
EDF header character encoding: The EDF specification says that only ASCII characters are allowed. EDFlib will automatically convert characters with accents, umlauts, tilde, etc. to their "normal" equivalent without the accent/umlaut/tilde/etc.
The description/name of an EDF+ annotation on the other hand, is encoded in UTF-8.
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