The EDF specs do not prescribe standard texts for the EDF-header fields 'label' and 'physical dimension'. Therefore, EDF readers and analyzers cannot fully automatically:

• distinguish EEG signals from ECG, EMG and so on
• use the location of sensors, such as EEG electrode positions (for mapping)
• retrieve standard (usually SI) signal dimensions (for amplitude calibration)

The listed texts comply with the official specs and therefore do not cause any incompatibility with EDF software. EDF import (reader/browser, analysis) software should abide by the official specs and not depend on the standard texts on this page. However, if the software detects that the imported file does contain standard texts, it can automatically recognize labels and dimensions. Even smarter software can correct obvious mistakes or suboptimal attempts to use the standard texts.

Standard texts are not required for EDF compatibility. However, they reduce the probability for errors and avoid the need for user input in some types of automatic analysis programs. Therefore, it is wise to use the standard texts wherever possible.

The standard texts have a simple standard structure in which simple standard components are put. Both are specified below.

Structure of the standard texts.
 

The standard 'label' structure.
The EDF 'label' field offers 16 ASCII characters. The standard structure that we propose here consists of three components, from left to right:

• Type of signal (for example EEG).
• A space.
• Specification of the sensor (for example Fpz-Cz).

The standard 'physical dimension' structure.
The EDF 'physical dimension' field offers 8 ASCII characters.  The standard structure that we propose here consists of two components, from left to right:

• Prefix (for example u).
• Basic dimension (for example V).

Powers in a basic dimension  (for instance the basic dimension of a volume is: meters to the power 3) are noted by ^. Examples are m^3 for a volume or m/s^2 for acceleration. Some basic dimensions involve more complicated mathematical expressions, such as for instance in  kg*m/s^2. Of course, first everything between brackets must be evaluated. Then the evaluation order is:  prefix - powers - multiplication - division. In this example, the evaluation is ((kg)*m)/(s^2). As another example, km^2 means (1000m)^2, not 1000(m^2).

P.M.
These 16- and 8-character fields contain the standardized information about the type of signal and its dimension. Further, non-standardized, information can be stored in the 80-character fields 'Transducer Type' and 'Prefiltering'.

Components for the standard structures.

Table 1. Standard components for a variety of signals. The standard 'label' contains a 'Type' of signal and a 'Specification' component. The standard 'physical dimension' contains a 'Prefix' and a 'Basic' dimension component. The prefix multiplies or divides the basic dimension by factors of 10 till 10^24. Standard prefixes are listed in table 2.

As an illustration of the versatility of EDF, the table also shows some signals that have not yet been, but can easily be, applied in EDF files. In fact, any time-varying signal, from geology to medicine or the stock market, can be stored in EDF files. We are deliberately keeping the table incomplete for a lot of signals until these would be frequently applied in EDF files. At that time we would like to use the expertise from professionals in that field of application.
 

Signal	Standard Label (16 ascii)			Standard Dimension (8 ascii)
	Type	Specification	Example	Basic	Example
Length or distance	Dist	any	Dist A'dam-R'dam	m	km
Area	Area	any	Area pupil	m^2	mm^2
Volume	Vol	any	Vol moon	m^3	Mm^3
Duration	Dur	any	Dur AP	s	ms
Velocity	Vel	any	Vel light	m/s	Mm/s
Mass	Mass	any	Mass body	g	mg
Angle	Angle	any	Angle azimuth	rad, deg	rad, deg
Percentage	%	any	%	%	%
Value (money)	Value		Value	table 2	NLG
Electroencephalogram	EEG	see below	EEG Fpz-Cz	V	uV
Electrocardiogram	ECG		ECG	V	mV
Electroöculogram	EOG		EOG horizontal	V	mV
Electroretinogram	ERG		ERG left	V	uV
Electromyogram	EMG		EMG LAT	V	mV
Magneto encephalogram	MEG		MEG
Magneto cardiogram	MCG		MCG
Temperature	Temp	any	Temp rectal	K, degC or degF	degC
Respiration	Resp	table 3	Resp abdomen
Oxygen saturation	SaO2	any	SaO2 finger	%
Light	Light	any	Light sternum
Sound	Sound	any	Sound trachea
Events	Event	any	Event button

The 'Specification' of an EEG signal consists of the location of the 'positive' electrode (that is the one whose potential adds to the signal) immediately followed by a '-' (minus) sign, which is then immediately followed by the location of the 'negative' electrode (that is the one whose potential is subtracted from the signal). For example, if the positive and negative electrode locations are Fpz and Cz, respectively, then the 'Specification' is Fpz-Cz and the standard label reads 'EEG Fpz-Cz       '. Standard 'positive' and 'negative' locations for EEG electrodes are in table 2.
    In some cases the 'positive' or 'negative' electrode is an average over more than one electrode. In that case, define this average between round brackets. For instance, the EEG between C3 and linked earlobes has label 'EEG C3-(A1+A2)  '. If one of the electrode locations is unknown or irrelevant (for instance because it is only used as a temporary reference), then use the text Ref, for instance in 'EEG C3-Ref       '. If more of such locations exist, then use the text Ref1, Ref2, and so on.

Table 3. Standard specifications for respiration signals

chest

abdomen

oral

nasal

oro-nasal

Back to EDF