delay in stream data from OpenBCI_GUI to Matlab 2019

FredyMunozFredyMunoz USA
in OpenBCI_GUI
Hi, 
I am using the Cyton board and the dongle to receive data from 8 channels in a Windows PC. I am able to visualize all the 8 signals in real time on the OpenBCI_GUI. However, when I set up the LSL from this GUI to stream data into Matlab, I have noticed that the stream data in Matlab has a long delay of approximately 20 to 23 seconds. In Matlab, from the command window I use: vis_stream. This allows me to visualize the 8 signals with the long delay of 20 s. I tried changing different parameters (from the vis_stream pop up window) such as maximum time range to buffer, sampling rate for display and refresh rate for display but the long delay of over 20 s in the stream data persisted. 
I also tried creating different Matlab scripts where I use pull_sample() or pull_sample(0) or pull_chunk() functions and plot the stream data but obtain the same long delays in the stream data. 
Any advice will be greatly appreciate it.

Thanks,
Fredy

Comments

  • retiututretiutut Louisiana, USA
    edited August 2019

    @FredyMunoz

    I am the developer who fixed LSL output from the GUI. Before, it was completely broken. The output from the GUI using LSL is very strait forward, with little room for error. I have successfully tested LSL networking using OpenVibe ONLY with no delays or issues of any kind!

    Please provide an example Matlab sketch/program so that myself and others can test this and replicate/resolve any issues with GUI->MATLAB integration.

  • retiututretiutut Louisiana, USA

    ALL MATLAB USERS: Are there any obvious errors in the OpenBCI MATLAB Doc???

    If so, please make an issue here on the new Docs repo.

  • FredyMunozFredyMunoz USA
    edited February 2020

    Hi,
    Please see below the script that I use with the pull.sample() function. I put side by side the real-time signals displayed on the OpenBCI_GUI and the figure plotted in the Matlab script. I notice a delay greater than 20 s in the signals displayed by the Matlab script.
    Thanks for your help.

    disp('Loading the library...');
lib = lsl_loadlib();
disp('Resolving an EEG stream...');
result = {};
while isempty(result)
    result = lsl_resolve_byprop(lib,'type','EEG'); end

disp('Opening an inlet...');
inlet = lsl_inlet(result{1});
disp('Now receiving data...');
fs=250;%Hz
duration=1;%seconds
totalSamples=duration*fs;
displayTime=10;%in seconds
EMGdata=zeros(totalSamples,8);
timeStamp=zeros(totalSamples,1);
displayRawSignals=zeros(displayTime*fs,8);

stop=0;
counter=0;
while 1
   [vec,ts] = inlet.pull_sample();
   if isempty(vec)~=1
     counter=counter+1;
     if counter<=totalSamples
        EMGdata(counter,1:8)=vec;
        timeStamp(counter,1)=ts;
     else
        counter=0;
        stop=1;
     end
   end     
    if stop==1%
        displayRawSignals=circshift(displayRawSignals,-totalSamples);
        displayRawSignals(displayTime*fs-totalSamples+1:displayTime*fs,:)=EMGdata;
        figure (1)
        plot(displayRawSignals(:,1),'r')
        stop=0; 
     end    
end
  • retiututretiutut Louisiana, USA

    Moving this to an OpenBCI GUI Issue: https://github.com/OpenBCI/OpenBCI_GUI/issues/595

    Looks like LSL streaming needs a handful of work, and there is a need to prioritize LSL streaming for the next GUI releases.

  • jeyemjeyem

    Hey there,
    I replicated the 23seconds delay issue from GUI -> MATLAB using my own MATLAB scripts.
    Is there currently any known configuration where live streaming from Cyton to MATLAB works? Maybe Python --> MATLAB?

    Thanks for your help.

  • retiututretiutut Louisiana, USA
    edited October 2019

    Everyone please try 4.1.6. There was a bug that didn't allow multiple LSL streams to work properly, and it has been fixed.

    I've written some simple LSL python scripts: https://github.com/OpenBCI/OpenBCI_GUI/tree/master/Networking-Test-Kit/LSL. This allowed me to debug the issue.

    Also, I am running Matlab2019b with liblsl-Matlab-1.10 added to my Matlab Path, and I do not see a delay!

  • retiututretiutut Louisiana, USA
    edited October 2019

    All of these people experiencing a delay have to have something in common... Not quite sure what it is.

    Please refer to the above screenshot. I was not able to replicate any type of delay using: Matlab, OpenVibe, or Python.

  • retiututretiutut Louisiana, USA

    @jelenaj also reports a delay over LSL. https://openbci.com/forum/index.php?p=/discussion/2321/openvibe-openbci-ganglion#latest

  • retiututretiutut Louisiana, USA

    @FredyMunoz Are you using 32bit or 64bit apps? GUI and Matlab?

  • CassaniCassani

    Hey,
    Testing the OpenBCI GUI to stream over LSL from the Cython board, and I was able to replicated the 23 s delay.
    My system is W10 64-bits, and the OpenBCI GUI is 4.1.7, and the LSL stream was read from Python3 using pylsl.
    Later, I used OpenBCI_LSL to stream data from the Cython board over LSL. And using the same Python3 codes to received data, and there was not noticeable delay.

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