Speed-mode setting on BioSemi AD box

hkeyes · Post by **hkeyes** » Mon Sep 01, 2008 10:53 am

Hello,

We have just purchased a 64-channel BioSemi system. I am unsure as to which speed-mode setting I should be using. I will be recording from 64 electrodes plus 8 flat-type active electrodes (for EOG). Can anyone tell me what the most suitable speed-mode setting would be for this set-up?

From the table in the manual, it appears that speed-mode setting 4 is appropriate- 2048 (2kHz), 232 + 8. In the sensors box, it says "yes". Does "sensors" in this case refer to the 8 EOG electrodes?

Thanks,

Helen Keyes

School of Psychology
UCD Dublin

Post by **Coen** » Mon Sep 01, 2008 12:21 pm

You can use speedmodes 4, 5 or 6. Speedmode 6 will give you a maximum sample-rate of 8 kHz, and a minimum sample rate of 128 Hz (by using the "decimation" option in software).

"Sensors" refers to the extra optional sensors connected to the Aux inputs (GSR, Plethysmograph, Respiration, ect, see http://www.biosemi.com/accessoires.htm).

Best regards, Coen (BioSemi)

hkeyes · Post by **hkeyes** » Mon Sep 01, 2008 12:43 pm

Thanks very much Coen, that's really helpful.

Helen

Post by **Coen** » Tue Sep 02, 2008 12:28 pm

Just one extra remark: keep in mind that the analog bandwidth is approx. 1/5th of the sample-rate (-3 dB point is indicated in the right sidebar). So, ensure that you select the sample-rate high enough to retain sufficient high frequency information in the data. For most EEG work, it is recommended to not go lower than 512 Hz (-3 dB cutoff of the anti-aliasing filter is at 104 Hz). By the way, you can always downsample the data off-line with the "decimator" tool, available from http://www.biosemi.com/download/Decimator.zip.

Best regards, Coen (BioSemi)

hkeyes · Post by **hkeyes** » Tue Sep 02, 2008 12:53 pm

Thanks Coen,

Helen