[Eeglablist] pop_iirfilt warning? Matrix is close to singular or badly scaled

[Simon-Shlomo Poil]

Dear eeglab list,

I am using pop_iirfilt to highpass my eeg data at 0.5 Hz, and get the
following warning:

.Warning: Matrix is close to singular or badly scaled.
         Results may be inaccurate. RCOND = 6.130406e-017.
> In filtfilt at 81
  In iirfilt at 213
  In pop_iirfilt at 234

However, if I resample my data from 1000 Hz to 500 Hz the warning
disappears? At first, I thought this was due to some extreme values
being smoothed by the resampling; I, however, do not find any extreme
values in the data.

Does somebody have a clue why the iir filter does not work with a high
sampling frequency?


Best regards,
-- 
Simon-Shlomo Poil

Neuronal Oscillations and Cognition Group (NOC)
Department of Integrative Neurophysiology (INF)
Center for Neurogenomics and Cognitive Research (CNCR)
Neuroscience Campus Amsterdam
VU University Amsterdam
De Boelelaan 1085, Room B-435
1081 HV Amsterdam, The Netherlands

E-mail: simonshlomo.poil at cncr.vu.nl
Phone: +31 20 5989408
Webpage: http://www.poil.dk and http://www.cncr.nl