edfwrite

Create or modify EDF or EDF+ file

Since R2021a

Description

Create an edfwrite object to write or modify a European Data Format (EDF) or EDF+ file.

Creation

Syntax

edfw = edfwrite(filename)

edfw = edfwrite(filename,hdr,sigdata)

edfw = edfwrite(filename,hdr,annotationslist)

edfw = edfwrite(filename,hdr,sigdata,annotationslist)

edfw = edfwrite(___,Name,Value)

Description

edfw = edfwrite(filename) creates an edfwrite object for an existing EDF or EDF+ file specified by filename.

edfw = edfwrite(filename,hdr,sigdata) creates an edfwrite object and a new EDF or EDF+ file with signal data, sigdata. File properties are specified in the header structure, hdr.

edfw = edfwrite(filename,hdr,annotationslist) creates an edfwrite object and a new EDF or EDF+ file with annotations, annotationslist.

edfw = edfwrite(filename,hdr,sigdata,annotationslist) creates an edfwrite object and a new EDF or EDF+ file with signal data and annotations.

edfw = edfwrite(___,Name,Value) sets Properties using name-value arguments. You can specify DataRecordTimes, AnnotationsEncoding, and InputSampleType.

Input Arguments

filename — Name of EDF or EDF+ file

character vector | string scalar

Name of EDF or EDF+ file, specified as a character vector or string scalar.

Depending on the location of the file, filename can take one of these forms.

Location	Form
Current folder or folder on the MATLAB® path	Specify the name of the file in filename. Example: 'data.edf'
File in a folder	If the file is not in the current folder or in a folder on the MATLAB path, then specify the full or relative path name. Example: 'C:\myFolder\data.edf' Example: 'myDir\myFile.ext'

Note

edfwrite does not support EyeLink^® EDF files.

Data Types: char | string

hdr — Header

structure

Header details, specified as a structure. See edfheader for more information.

Data Types: struct

sigdata — Signal data

matrix | cell array

Signal data, specified as a numeric matrix with one or more columns or a cell array of numeric vectors.

Data Types: double | cell

annotationslist — Annotations

timetable

Annotations, specified as a timetable containing these variables:

• Onset — Time at which the annotation occurred, expressed as a duration indicating the number of seconds elapsed since the start time of the file. Use Onset to specify the rowTimes in the timetable.

• Annotations — A string that contains the annotation text.

• Duration — A duration scalar that indicates the duration of the event described by the annotation. If the file does not specify an annotation duration, this variable is returned as NaN.

Data Types: table

Properties

File Properties

Filename — File name

string scalar

This property is read-only.

File name, returned as a string scalar.

Example: "ecg_20200411_120.edf"

Data Types: string

FileType — File type

"EDF" | "EDF+"

File type, returned as "EDF" or "EDF+".

Data Types: string

FileModDate — Date last modified

string scalar

This property is read-only.

Date last modified, returned as a string scalar with the date and time the file was last modified.

Example: "11-Apr-2020 15:38:37"

FileSize — File size in bytes

integer scalar

This property is read-only.

File size in bytes, returned as an integer scalar.

Example: 4040992

Data Types: double

Header Properties

Version — Data format version

"0"

This property is read-only.

Data format version, returned as "0".

Data Types: string

Patient — Patient identification details

string scalar

This property is read-only.

Patient identification details, returned as a string scalar. Patient identification details can include Patient ID, sex or gender, birth date in 'dd-MMM-yyyy' format, and name.

Example: "X F X 120 04-JUL-1982"

Data Types: string

Recording — Recording identification details

string scalar

This property is read-only.

Recording identification details, returned as a string scalar. Recording identification details may include its start date and time, the ID of the technician that made the recording, and the ID of the equipment that made the recording.

Example: "Startdate 04-JUL-1982 X X X"

Data Types: string

StartDate — Recording start date

string scalar

This property is read-only.

Recording start date, returned as a string scalar in 'dd.MM.yy' format.

Example: "04.07.82"

Data Types: string

StartTime — Recording start time

string scalar

This property is read-only.

Recording start time, returned as a string scalar in 'HH.mm.ss' format.

Example: "17.16.37"

Data Types: string

HeaderBytes — Header size in bytes

integer scalar

This property is read-only.

Header size in bytes, returned as an integer scalar. HeaderBytes is given by (256 + NumSignals × 256) bytes. The first 256 bytes correspond to a static header and are required for all EDF and EDF+ files. The other bytes depend on the number of signals present in the data records.

Example: 2048

Data Types: double

Reserved — EDF+ interruption information

"EDF+C" | "EDF+D" | ""

This property is read-only.

EDF+ interruption information, returned as "EDF+C" or "EDF+D" for EDF+ compliant files.

• "EDF+C" — The recording is continuous: There are no interruptions and all data records are contiguous, such that the start time of each data record coincides with the start time of the previous record plus its duration.

• "EDF+D" — The recording is discontinuous with interruptions between consecutive data records.

For files that are not EDF+ compliant, this property is an empty string ("").

Data Types: string

NumDataRecords — Number of data records in file

integer scalar

This property is read-only.

Number of data records in file, returned as an integer scalar.

Note

If filename is not EDF compliant, NumDataRecords can be set to -1 when the number of data records is unknown. If filename is EDF compliant, NumDataRecords must be set to a positive integer. If filename has Reserved set to a nonempty string and NumDataRecords set to -1, edfinfo throws an error.

Data Types: double

DataRecordDuration — Duration of each data record

duration scalar

This property is read-only.

Duration of each data record, returned as a duration scalar.

Data Types: duration

NumSignals — Number of signals in file

integer scalar

This property is read-only.

Number of signals in file, returned as an integer scalar.

Data Types: double

DataRecordTimes — Start time of each data record

duration vector

Start time of each data record, returned as a duration vector. DataRecordTimes must be specified for an EDF+ file with discontinuous record start times. The vector must be equal in length to NumDataRecords.

Data Types: duration

Signal Properties

SignalLabels — Signal names

string vector

This property is read-only.

Signal names, returned as a string vector of length NumSignals.

["Thorax 1";"Abdomen 3"]

Data Types: string

TransducerTypes — Transducer details

string vector

This property is read-only.

Transducer details, returned as a string vector of length NumSignals. Each element of TransducerTypes contains details about the transducer used to obtain the corresponding signal in SignalLabels.

Example: ["AgAgCl electrodes";"thermistor"]

Data Types: string

PhysicalDimensions — Signal data units

string vector

This property is read-only.

Signal data units, returned as a string vector of length NumSignals. Each element of PhysicalDimensions contains the measurement units used to express the values of the corresponding signal in SignalLabels.

Example: ["uV";"mV"]

Data Types: string

PhysicalMin — Signal minimum physical value

numeric vector

This property is read-only.

Signal minimum physical value, returned as a numeric vector of length NumSignals. Each element of PhysicalMin contains the minimum physical value of the corresponding signal in SignalLabels.

Data Types: double

PhysicalMax — Signal maximum physical value

numeric vector

This property is read-only.

Signal maximum physical value, returned as a numeric vector of length NumSignals. Each element of PhysicalMax contains the maximum physical value of the corresponding signal in SignalLabels.

Data Types: double

DigitalMin — Signal minimum digital value

numeric vector

This property is read-only.

Signal minimum digital value, returned as a numeric vector of length NumSignals. Each element of DigitalMin contains the minimum digital value of the corresponding signal in SignalLabels.

Data Types: double

DigitalMax — Signal maximum digital value

numeric vector

This property is read-only.

Signal maximum digital value, returned as a numeric vector of length NumSignals. Each element of DigitalMax contains the maximum digital value of the corresponding signal in SignalLabels.

Data Types: double

Prefilter — Signal data units

string vector

This property is read-only.

Signal data units, returned as a string vector of length NumSignals. Each element of Prefilter contains details about the filters, if any, used to preprocess the corresponding signal in SignalLabels.

Example: ["HP:10Hz LP:80Hz N:60Hz";"HP:0.1Hz LP:90Hz N:60Hz"]

Data Types: string

NumSamples — Number of samples in signal

numeric vector

This property is read-only.

Number of samples in signal, returned as a numeric vector of length NumSignals. Each element of NumSamples contains the number of samples in the corresponding signal in SignalLabels.

Data Types: double

SignalReserved — Additional signal information

string vector

This property is read-only.

Additional signal information, returned as a string vector of length NumSignals. Each element of SignalReserved contains additional information, if any, about the corresponding signal in SignalLabels.

Data Types: string

InputSampleType — Input sample type of signal data

"digital" (default) | "physical"

Input sample type of signal data, returned as "digital" or "physical". The function defaults to "digital" and writes the signal data into the file with no digital scaling. If 'InputSampleType' is set to "physical", then edfwrite applies digital scaling to the signal data.

Data Types: string

Annotation Properties

Annotations — Annotations present in signal records

timetable

This property is read-only.

Annotations present in signal records, returned as a timetable containing these variables:

• Onset — Time at which the annotation occurred, expressed as a duration indicating the number of seconds elapsed since the start time of the file.

• Annotations — A string that contains the annotation text.

• Duration — A duration scalar that indicates the duration of the event described by the annotation. If the file does not specify an annotation duration, this variable is returned as NaN.

Data Types: table

AnnotationsEncoding — Encoding format

"US-ASCII" (default) | "UTF-8" | "LATIN1"

Encoding format used to write annotations into the file, returned as "US-ASCII", "UTF-8", or "LATIN1".

Data Types: string

Object Functions

addAnnotations	Add annotations to EDF or EDF+ file
addSignals	Add new signals to EDF or EDF+ file
deleteAnnotations	Delete annotations from EDF or EDF+ file
deleteSignals	Delete signals from EDF or EDF+ file
modifyAnnotations	Modify annotations in EDF or EDF+ file
modifyHeader	Modify header details of EDF or EDF+ file
modifySignals	Modify signals in EDF or EDF+ file

Examples

Create EDF+ File with Annotations

Load EMGdata.mat into the workspace. The file contains eight channels of surface electromyography (EMG) data [1] recorded from eight arm muscles. The data is available at www.sce.carleton.ca/faculty/chan/index.php?page=matlab. The sample rate is 1000 Hz. Plot the signals.

load EMGdata

fs = 1000;
t = 0:1/fs:(size(data,1)-1)/fs;
stackedplot(t,data)

The bursts of increased signal amplitude correspond to different forearm motions that last 3 seconds each. EMGindex.mat contains the type of motion and the start index (sample) of each motion in two variables: motion and start_index. The motion types are:

1. Hand open

2. Hand close

3. Wrist flexion

4. Wrist extension

5. Supination

6. Pronation

7. Rest

Load the data into the workspace.

load EMGindex

Create a timetable of annotations.

1. Use Onset to specify the row times. Onset contains the start index of each motion in seconds.

2. Annotations specifies the types of motion as a string array.

3. Duration specifies the duration of each motion in seconds.

Onset = seconds(start_index./fs);
Annotations = string(motion);
Duration = seconds(ones(length(Onset),1)*3);

annotationslist = timetable(Onset,Annotations,Duration);

Use edfheader to create a header structure for the EDF+ file and set the properties. See edfheader for more information.

hdr = edfheader("EDF+");
hdr.NumDataRecords = 1;
hdr.DataRecordDuration = seconds(length(data(:,1))/fs);
hdr.NumSignals = 8;
hdr.SignalLabels = ["F1" "F2" "F3" "F4" "F5" "F6" "F7" "B1"];
hdr.PhysicalDimensions = repelem("mV",8);
hdr.PhysicalMin = min(data);
hdr.PhysicalMax = max(data);
hdr.DigitalMin = repmat(-32768,1,8);
hdr.DigitalMax = repmat( 32767,1,8);

Write an EDF+ file containing the header structure, signal data, and annotations. Specify the input sample type as physical. The file is saved in the current working directory.

edfw = edfwrite("armEMG.edf",hdr,data,annotationslist, ...
    "InputSampleType","physical");

Display information about the file.

edfinfo("armEMG.edf")

ans = 
  edfinfo with properties:

              Filename: "armEMG.edf"
           FileModDate: "05-Sep-2024 18:33:12"
              FileSize: 4803836
               Version: "0"
               Patient: "1234567 F 05-SEP-2024 Patient_1"
             Recording: "Startdate 05-SEP-2024 MW_1234567 MW_Inv_01 MW_Eq_01"
             StartDate: "05.09.24"
             StartTime: "18.33.11"
           HeaderBytes: 2560
              Reserved: "EDF+C"
        NumDataRecords: 1
    DataRecordDuration: 300.03 sec
            NumSignals: 8
          SignalLabels: [8x1 string]
       TransducerTypes: [8x1 string]
    PhysicalDimensions: [8x1 string]
           PhysicalMin: [8x1 double]
           PhysicalMax: [8x1 double]
            DigitalMin: [8x1 double]
            DigitalMax: [8x1 double]
             Prefilter: [8x1 string]
            NumSamples: [8x1 double]
        SignalReserved: [8x1 string]
           Annotations: [28x2 timetable]

You can use EDF File Analyzer to view the signals and annotations stored in the file. Use the Signal Separation option to separate the signals for better visualization.

Delete the EDF+ file. Comment out this code if you want to keep the file.

delete armEMG.edf

Tips

• To create an EDF+ file containing only annotations, specify NumDataRecords and NumSignals as 0, DataRecordDuration as a duration scalar with value 0, and all signal properties as empty.

• Launch the EDF File Analyzer app to visualize the signals in your EDF or EDF+ file.

References

[1] Chan, Adrian D.C., and Geoffrey C. Green. 2007. "Myoelectric Control Development Toolbox". Paper presented at 30th Conference of the Canadian Medical & Biological Engineering Society, Toronto, Canada, 2007.

[2] Kemp, Bob, Alpo Värri, Agostinho C. Rosa, Kim D. Nielsen, and John Gade. “A Simple Format for Exchange of Digitized Polygraphic Recordings.” Electroencephalography and Clinical Neurophysiology 82, no. 5 (May 1992): 391–93. https://doi.org/10.1016/0013-4694(92)90009-7.

[3] Kemp, Bob, and Jesus Olivan. "European Data Format 'plus' (EDF+), an EDF Alike Standard Format for the Exchange of Physiological Data." Clinical Neurophysiology 114, no. 9 (2003): 1755–1761. https://doi.org/10.1016/S1388-2457(03)00123-8.

Version History

Introduced in R2021a