All new LSL tools: now directly available on our own website
by Dr. Alex Kreilinger
Technical Product Manager (Brain Products)
Brain Products’ LSL connectors for actiCHamp (Plus), LiveAmp, and BrainAmp have been downloaded from the Brain Products GitHub page many times and are being used in many ongoing projects that involve the powerful and versatile LSL protocol. That said, we observed that there was not much contribution coming from the community, and that we were maintaining the source code basically on our own anyway.
Based on this development, we decided to update the code for all main LSL connectors in-house and provide the applications as free software from now on. As a result, we are proud to announce the official release of the following applications on our own website:
All of these stand-alone applications can be downloaded from the LSL tools section and we provide comprehensive manuals for the three connectors and for the LSL Viewer.
Our motivation for releasing the three connectors anew was mainly based on providing a harmonized experience with similar user interfaces wherever possible, while still supporting the individual characteristics of our different amplifiers. In addition, we wanted to increase performance, mainly with respect to the latency between the hardware-based LSL streams and other LSL streams on the local network. We also included an impedance measure functionality for all connectors, so that it is no longer necessary to switch between BrainVision Recorder and LSL connector.
Here is a breakdown of the most important changes
When starting the new connectors, you will immediately notice that they all have the same structure and basic functionality. It’s only in the details that the connectors differ between each other. Figures 1 and 2 demonstrate the new look based on LiveAmp, without an active connection and with an active connection in the middle of setting up the configuration.
Figure 1: BrainVision LSL Connector for LiveAmp. On the left, all the channels and modules can be seen when an amplifier has been connected. On the right, the device settings can be adjusted, depending on the different configuration options of the specific amplifier, even depending on the connected accessories (for example the STE compact). LSL settings and default operations, such as the new impedance check are similarly placed in the lower right corner for all connectors.
Figure 2: BrainVision LSL Connector for LiveAmp with a connected amplifier with Sensor & Trigger Extension. The configuration can be saved and loaded in future sessions. The Trigger Channels and Modules sections provide extra ways to fine-tune the setup and give an overview of the connected accessories.
Many people who are using LSL want to synchronize EEG data streams with signals from other sources, often coming from other hardware devices with their own LSL connector, or even from signals or markers coming directly from software sources. In these cases, it is important to either be aware of the hardware-specific latency, to correct it online, or to even minimize it as much as possible. In several previous articles we have pointed out that such considerations may be important, depending on the setup, for example here or here.
In this regard, we are proud to report two major improvements:
The following figures demonstrate comparisons between the old and new LSL connectors for LiveAmp and BrainAmp. Time stamps of three simultaneous events were compared after 500 repetitions: The onset of a flashing square (‘PS’), the appearance of hardware triggers in the LSL data stream (‘HW’), and the ‘LSL’ time stamps coming directly from the Presentation® software. Please read here and here for more information on how the timing was verified. Note: latency values may vary between individual setups.
Figure 3: Difference between latencies for LiveAmp. Left: Former LSL-LiveAmp connector as available on GitHub. Right: New BrainVision LSL Connector for LiveAmp. The same settings were used for both recordings on top (1 kHz, 1 EEG channel and 1 AUX channel) and both recordings on the bottom (250 Hz, 32 EEG channels, 1 AUX channel).
Figure 4: Difference between latencies for BrainAmp. Left: Former BrainAmp Series LSL connector as available on GitHub. Right: New BrainVision LSL Connector for BrainAmp. The same settings (5 kHz, 48 channels) were used for both recordings. The latency decreased from 53.76 ms to 3.5 ms.
As the LSL connector for actiCHamp was already able to provide latencies below 5 ms, there was not much room for improvement. For the new connector, rest assured that we have maintained its performance while enhancing its usability.
A historic problem of the original LSL connectors for our amplifiers was the jitter inherent to the “Unsampled String Markers” setting and the consequential recommendation to use the “EEG Channel” option instead. Now, the string markers are dejittered within the connector and their timing information is as reliable as the LSL markers in the additional channel, and we believe that many people will find these markers easier to work with when they are saved as pairs of string and time stamp.
Another obstacle for using LSL was the fact that the users typically had to switch between BrainVision Recorder and the LSL connector when setting up the electrodes and verifying the signal quality. The typical process was to use Recorder, mount all of the electrodes and then use Impedance mode in Recorder to optimize the contact between electrodes and skin. As soon as the impedance values were low enough, Recorder was closed, and the LSL connector was started to provide online data streams.
Now, all of these steps can be taken with all of the new connectors. Simply click on the Check Impedances button and get feedback on all the impedance values directly from within the LSL connector. When the impedances have reached acceptable values, the stream can immediately be started.
Even though there is a lot of information on the LSL solutions from Brain Products out there, it is still important to provide concise manuals in an easy to find place. With the release of the new LSL connectors and the LSL Viewer on our new LSL tools section, we also provide a manual for the three LSL connectors and an additional manual for the LSL Viewer. We believe that with these sources of information and additional articles, for example on bci.plus or the recent support article, we provide a very good starting point.
That said, please do not hesitate to ask any questions that may still be open or send us feedback for these new uploads. We are always happy to receive feedback from our customers and wish you all the best with your future projects involving LSL and Brain Products equipment.