[Eeglablist] EEG filtering

[Eriksen, Jeffrey :LGS Neurodiagnostics]

Mori,

This stems from the old days of clinical EEG amplifiers and analog filters. Historically, early EEGers used the concept of a time-constant, which basically corresponded to the decay time (to half amplitude or 3 dB or the like) of an impulse applied to a simple resistor-capacitor (RC) filter. Typical time-constants were 1.0 or 0.1 seconds that were easy numbers for people to deal with. When the RC filter is considered in more modern terms as a low-cut or high-pass filter, we shift to using Hz. Because of the math of sines and cosines, a factor of 2-pi gets applied, which leads to these funny numbers you mention.

The above is all from memory, look it up on Google to get the particulars, and the exact conversion. Clinical EEG machines still give the user the option of using time-constant or Hz for the lo-cut/hi-pass filter settings, even though no one uses simple RC filters anymore.

-Jeff


From: eeglablist-bounces at sccn.ucsd.edu [mailto:eeglablist-bounces at sccn.ucsd.edu] On Behalf Of mori larin
Sent: Friday, February 20, 2015 5:22 AM
To: eeglablist
Subject: [Eeglablist] EEG filtering

Dear all,

I have a question about the low cut off frequency for EEG filtering.
My question is why people select exactly 0.016 Hz and/or 0.16 Hz low cut off frequency?
What do these value refer to and why exactly these values?

Many thanks,
Mori

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