[FieldTrip] Calculating the cross spectral density matrix

[陈雪]

Dear all:
       I calculate the cross spectral density matrix and my data from
rest. I want do beta-band activity(14-30Hz).so I use a center frequency of
about 22 Hz.we select a time window of 0.5s.I do this as follow:
        cfg = [];
cfg.toilim = [0.5 1];
dataP = ft_redefinetrial(cfg, data_org);
  cfg = [];
 cfg.method    = 'mtmfft';
 cfg.output    = 'powandcsd';
 cfg.tapsmofrq = 8;
 cfg.foilim    = [22 22];
 freqP = ft_freqanalysis(cfg, dataP);

And i got this wrong message

??? Error using ==> dpss at 45
Time-bandwidth product NW must be less than N/2.
Error in ==> ft_specest_mtmfft>double_dpss at 303
tap = dpss(double(a), double(b), varargin{:});
Error in ==> ft_specest_mtmfft at 115
        tap =
        double_dpss(ndatsample,ndatsample*(tapsmofrq./fsample))';

Error in ==> ft_freqanalysis at 526
        [spectrum,ntaper,foi] = ft_specest_mtmfft(dat, time,
        'taper', cfg.taper, options{:}, 'feedback', fbopt);

thanks for your attention.
best,
mengtongxiao
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