edfwrite can not export my signal properly

Hi Everyone,

I would like to export my signal in edf format, using MATLAB 2022a (academic use). I wrote the following code for a representative EEG:

EEG=randn(1,360000);
%% edfheader
hdr = edfheader("EDF+");
hdr.Patient = "Mouse F";
hdr.Recording = "INH50";
hdr.StartDate = "13.09.23";
hdr.StartTime = "13.09.24";
hdr.Reserved = "EDF+C";
hdr.NumSignals = 1;
hdr.NumDataRecords = 1;
hdr.PhysicalMin = [-3200];
hdr.PhysicalMax = [3200];
hdr.DigitalMin = [-32768];
hdr.DigitalMax = [32767];
hdr.DataRecordDuration = seconds(360);
%%
edfwrite("EDFTEST.edf",hdr,EEG);

But when I use edfread to opne it, it shows:

edfread("EDFTEST.edf")

ans =

timetable

Record Time Signal_1

___________ _________________

0 sec {360000×1 double}

When I open the edf file in another program (Sigview), it is unusal:

Indeed, first I tried the code with my real EEG signal, and the exported signal was just some vertical lines!

It would be great if someone could tell me what my mistake in the code is, particularly in the header. I tried different values for PhysicalMin, PhysicalMax, DigitalMin, and DigitalMax, but there was no improvement.

I really appreciate your help, as I am stuck at this step!

Answer 1

[Taylor]

You're on the right track thinking about the PhysicalMin, PhysicalMax, DigitalMin, and DigitalMax values. You need to specify the InputSampleType as "physical" when calling edfwrite.

https://www.mathworks.com/help/signal/ref/edfwrite.html#mw_945f0980-3fd2-43fe-a30a-232cbc24f03a

A good indication that there is an issue involving ADC is the multi-level "clipping" you're seeing in your plot.

[Sadegh Rahimi]

Thanks for your suggestion. I will implement it to see, if it would solve the issue