[FieldTrip] High-pass filter - 0.1

[Roey Schurr]

Dear Emilie,

Try reading this thread and see if it helps:
http://mailman.science.ru.nl/pipermail/fieldtrip/2012-June/005360.html

The bottom line is, if you want a low highpass filer, you need to change
the order of the filter you're using.
In the example in the thread above, using a filter of order 5 helped Philipp
applying a 0.1 Hz highpass filter. So you could try using something like:
cfg.hpfiltord = 5;

Hope this helps!
Roey


On Sun, Aug 24, 2014 at 1:49 PM, Caspar, Emilie <e.caspar at ucl.ac.uk> wrote:

>  Thank you for your answer. The complete error message I have is this one,
> but I'm not able to decrypt it.
>
>  Error using filter_with_correction (line 44)
> Calculated filter coefficients have poles on or outside the unit circle
> and will not be stable. Try a higher cutoff
> frequency or a different type/order of filter.
>
>  Error in filter_with_correction (line 44)
>   error('Calculated filter coefficients have poles on or outside the unit
> circle and will not be stable. Try a
>   higher cutoff frequency or a different type/order of filter.');
>
>  Error in ft_preproc_bandpassfilter (line 148)
>   filt = filter_with_correction(B,A,dat,dir);
>
>  Error in preproc (line 299)
> if strcmp(cfg.bpfilter, 'yes'),     dat = ft_preproc_bandpassfilter(dat,
> fsample, cfg.bpfreq, cfg.bpfiltord,
> cfg.bpfilttype, cfg.bpfiltdir, cfg.bpinstabilityfix); end
>
>  Error in ft_preprocessing (line 559)
>       [cutdat{i}, label, time{i}, cfg] = preproc(dat, hdr.label(rawindx),
> tim, cfg, begpadding, endpadding);
>
>  Error in preprocessing_Libet (line 70)
>     allData_prepross      = ft_preprocessing(cfg);
>
>  It only occurs when I ask for a bpfilterrange from .1 to 30, or any
> values lower than .9.
>
>  Thanks!
>
>  Emilie
>
>
>
>  Le 11 août 2014 à 12:43, Eelke Spaak <eelke.spaak at donders.ru.nl> a écrit
> :
>
> Dear Emilie,
>
> The error message you include only specifies *where* in the code the
> error happened, not *what* the actual error was. Could you include the
> actual error as well? Perhaps someone can then help you fix it. (In
> general there is no fixed lower limit on filter low-/highpass
> frequency, although a practical limit could depend on your data.)
>
> Best,
> Eelke
>
> On 9 August 2014 09:31, Caspar, Emilie <e.caspar at ucl.ac.uk> wrote:
>
> Dear Fieldtrip members,
>
> I would like to apply to my data a bandpass filter from 0.016 (or at least
> 0.1) to 30 Hz
>
> bpfilterRange = [.1 30];
>
> However, it seems that Fieltrip doesn't accept small high-pass filter
> values. I have the following mistake :
>
>
> Error in preproc (line 299)
> if strcmp(cfg.bpfilter, 'yes'),     dat = ft_preproc_bandpassfilter(dat,
> fsample, cfg.bpfreq, cfg.bpfiltord,
> cfg.bpfilttype, cfg.bpfiltdir, cfg.bpinstabilityfix); end
>
> Error in ft_preprocessing (line 559)
>      [cutdat{i}, label, time{i}, cfg] = preproc(dat, hdr.label(rawindx),
> tim, cfg, begpadding, endpadding);
>
> Error in preprocessing_Libet (line 70)
>    allData_prepross      = ft_preprocessing(cfg);
>
> I also tried with 0.2, 0.5, and the minimum acceptable I found was 0.9,
> which is quite high.
>
> I wonder if the problem comes from my data (but I had no problems on others
> programs) or if there is a way to apply 0.1 high-pass filter on Fieldtrip?
>
> Thank in advance,
>
> Emilie
>
>
>
>
>
>
>
>
>
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