[Eeglablist] How to deal with 1/f noise in

Gangadhar Garipelli gangadhar.garipelli at epfl.ch
Fri Nov 19 02:43:11 PST 2010


Hello Derek,

Yes! indeed I am doing this already by applying a spatial smoothing
filter (SSF).

But this step works better if I band pass in the range (0.1 1)Hz to
remove any signals below 0.1Hz and common average reference the signals
before SSF! This is the reason, "I ran into the need for narrow bandpass"!

As a side note, I believe that 1/f noise is not only result of amplifier
but due to the inherent structure of neural oscillations [1] and could
also be due to slow variations in the gel-skin contact conductance.

[1] Gyorgy Buzsaki, Rhythms of the Brain, Oxford University Press, 1
edition,2006.

Thanks again! :-)
Ganga

On 11/17/2010 11:01 AM, derek eder wrote:
> If amplifier 1/f noise is suspected, one possible sanity check is to 
> record the same signal on multiple amplifier-channels and then sum* them.
> 
> The noise** contribution to the resulting average should be reduced by: 
>    1/sqrt(n.channels)
> 
> Compare the resulting low frequency activity with those from individual 
> channels.
> 
> Depending on the input-design / input-impedance of your amplifiers, 
> there are practical limits to the number of channels that one can 
> parallel from the same electrodes,  but 3 or 4 should not be a problem.
> 
> 
> ~Derek
> 
> 
> *   perhaps de-mean and scale first if your channels have offsets and/or 
> gain differences.
> ** assuming uncorrelated noise from individual channels
> 


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