Mind Monitor

Hi I want to calculate frontal asymmetry from the AF7 and AF8 electrodes.
I see the in the output csv files there are Alpha_AF7 and Alpha_AF8. I need to compute log(AF8 value/AF7 value) but I see lots of values in the csv file are negative (usually between -1 and 1), which doesn't allow me to compute the log. So is there any conversion I need to do to the values before bringing to the log to make sure they are all positive values? Also, when I import the file to the online graph tool on musemonitor.com, the numbers turn to around 100 (dB?). How is it calculated from the csv data?

Thanks!

The display values have a linear conversion from ~[-1:+1] to ~[0:100] by doing (x+1)x50.
I'm not sure why you want to log the values; To compare left vs right power, you can just use subtraction and see if the result is positive or negative.

Thank you for your reply. If I do (x+1)x50, does it make it in db unit? If so, then there is no need to do log, subtraction will do the work.

That formula just shifts the range.
There are no official units for what we're measuring here.
Bels are used to label any unit that has been derived from a log function and since the values are a log of Power Spectral Density this applies.

Thank you very much!