LSL - Bunch Markers - ".nedf file might be corrupted"

If you are sending markers to NIC via LSL and your computer does not meet the recommended specifications, you may see one of the following:

• Markers arriving in the recording appear "bunched" — multiple markers logged with almost no time separation, even though they were sent further apart.
• NIC reports that the resulting NEDF file is corrupted, or the file fails to open correctly after recording.

This tends to occur when markers are sent to NIC with very little time between each one, on lower-spec computers.

The root cause is currently under investigation by our team.

In this article, you will learn about a possible workaround: routing your EEG and marker streams through LabRecorder instead of recording directly in NIC.

We want to make sure that:

• Your marker events and EEG data are captured without corruption
• You have a way to verify your recording before relying on it for a study session
• You know what to do if the workaround does not resolve the issue

For this procedure you will need:

• NIC with LSL output enabled
• Your marker-sending software (e.g., E‑Prime, Presentation, PyschoPy or your own LSL marker application)
• LabRecorder (LSL Lab Recording software)
• Enobio / Starstim device
• SigViewer, to open and inspect the resulting XDF file

Section 1: Enable the LSL EEG stream in NIC

1. Open NIC.
2. Connect your Enobio/Starstim device.
3. Enable the LSL output setting in NIC.
4. Name it EEGOutlet

Section 2: Connect your marker software to LSL

1. Open your marker-sending software.
2. Configure it to send markers via an LSL outlet with a name different than EEGOutlet

Section 3: Record both streams in LabRecorder

1. Open LabRecorder.
2. Confirm that both the NIC EEG LSL stream and your marker LSL stream appear in the available streams list.
3. Select both streams.
4. Start the recording in LabRecorder.
5. Run your session as normal, sending markers through your marker software.
6. Stop the recording in LabRecorder once your session is complete.

LabRecorder will save your EEG and marker data together in a single XDF file.

Section 4: Verify the recording in SigViewer

1. Open SigViewer.
2. Open the XDF file created by LabRecorder.
3. Confirm that the EEG data is present and that markers appear at the correct, distinct timestamps.

→ If the file opens correctly and markers are correctly separated: the workaround has succeeded for this session. 

If you have questions about this known issue or the workaround above, contact support@neuroelectrics.com. Please include: your computer's specifications, the marker software and version you are using, the affected NEDF or XDF file, and the NIC log file.