Biosemi-OpenVibe-Matlab Channel Structure and Sampling Rate

Obtaining data from various hardware devices
Post Reply
yqjim111
Posts: 2
Joined: Sun Feb 07, 2021 1:55 am

Biosemi-OpenVibe-Matlab Channel Structure and Sampling Rate

Post by yqjim111 »

Hi everyone, we are developing a BCI tool using Matlab, Openvibe, and Biosemi MkII 128channels. Currently, run-time data is successfully transmitted from Biosemi-OpenVibe-Matlab through the LSL layer. However, three issues are confusing to us.

1, We are not sure if the runtime data from Openvibe follows the same data sequence in Biosemi (A, B, C, D bands, etc.). Is there a way to check what channel each column of data represents so we can make sure the runtime data-electrodes relationship matches the data from ActiView? (I plan to nudge some electrodes runtime to test but I wonder if anyone already found the information somewhere)

2, We received fewer data in Matlab runtime. It seems the frequency of data transmission is much lower (around 32 Hz) than it should be (256 Hz).

3, Once Openvibe Acquisition Server is connected and starts to send data to Matlab through the LSL layer. ActiView will freeze and not be able to receive any data from Biosemi. Is that because there is conflicting communication? Is there a quick way to solve it? Currently, we have to manually save runtime data in Matlab.

Thank you for your answers! :D

yqjim111
Posts: 2
Joined: Sun Feb 07, 2021 1:55 am

Re: Biosemi-OpenVibe-Matlab Channel Structure and Sampling Rate

Post by yqjim111 »

For Q1: Yes, I tested it and the channel structure matches the Biosemi structure (Band A-B-C-D etc)

For Q2: We kind of found the reason, because there is some preprocessing in our Matlab code, the rate of receiving data actually drops to around 80 Hz because of the computation load. Once we cancel out the preprocessing part, the receiving rate goes to around 4000 Hz, which matches the ADbox speed mode.

Don't worry anymore, found the decimation box in Openvibe.

Thibaut
Posts: 227
Joined: Wed Oct 31, 2018 9:14 am

Re: Biosemi-OpenVibe-Matlab Channel Structure and Sampling Rate

Post by Thibaut »

Hi,
I can't help you. But for your compute time I have an advise :
For me Matlab is not made for online processing. Python is a little better but if you wan't to make big process try to code a Box in C++. It's too hard if you never code in C++. But scripting langage are slower than other in general.
Thibaut

Post Reply