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Bug 1125 - remove DC offset prior to time-domain filtering in ft_preproc_*filter
| Status | CLOSED FIXED |
| Reported | 2011-11-08 16:00:00 +0100 |
| Modified | 2011-12-15 09:24:32 +0100 |
| Product: | FieldTrip |
| Component: | core |
| Version: | unspecified |
| Hardware: | PC |
| Operating System: | Windows |
| Importance: | P1 normal |
| Assigned to: | Johanna |
| URL: | |
| Tags: | |
| Depends on: | |
| Blocks: | |
| See also: |
Johanna - 2011-11-08 16:00:04 +0100
It should be more numerically correct to first remove mean of window that you're filtering. (that's how it's done in nut_filter2). Do this within each ft_preproc_*filter fcn. Then add mean back for output of each subfunction. Then preproc will do user-specified detrend/demean/polyremoval.
Jan-Mathijs Schoffelen - 2011-11-09 08:45:44 +0100
Created attachment 181 demonstrate the issue of DC-offset/linear trend with bpfilter
Johanna - 2011-11-14 14:57:52 +0100
Polyremoval, detrend, and demean are now above filtering. All other order has been preserved.
Johanna - 2011-11-18 14:29:44 +0100
ammended to previous comment: demean/detrend/polyremove added back *after* filtering to occur as well as *before* filtering. some residual mean/trend may exist after filtering.
Johanna - 2011-11-30 12:51:46 +0100
made change to only ft_preproc_bandstopfilter and ft_preproc_lowpassfilter, as doesn't make sense to add back the mean for the other two (highpass and bandpass). svn commit 4890.