[FieldTrip] about detrend

Alexander Nakhnikian Alexander_Nakhnikian at hms.harvard.edu
Fri Dec 5 23:11:22 CET 2014

Hi Yun,

Detrending a data set only removes the regression line.  It does not 
ensure that the process has zero mean, which translates to a zero DC 
component in frequency space.  The most direct way to ensure zero DC is 
simply to remove the trial mean from each epoch.



Alexander Nakhnikian, Ph.D.
Post Doctoral Fellow, Clinical Research Training Program
Harvard Medical School
Boston VA Healthcare System, Brockton MA

On 12/5/14, 4:20 PM, Yun Wen wrote:
> Hi all, I want to remove DC offset before applying the high-pass 
> filter. I  was wondering if I can achieve that by putting cfg.detrend 
> = 'yes' before cfg.hpfilter = 'yes', something like:
> cfg = [];
> cfg.dataset = filename_raweeg;
> cfg.detrend = 'yes';
> cfg.hpfilter = 'yes';
> cfg.hpfiltord = 2; % Order of the filter = 2.
> cfg.hpfreq = 0.1; % High-pass cutoff at 0.1 Hz;
> [data] = ft_preprocessing (cfg);
> Thank you in advance.
> Best,
> Yun
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