FieldTrip

Note that this reference documentation is identical to the help that is displayed in Matlab when you type “help ft_freqanalysis”.

  FT_FREQANALYSIS performs frequency and time-frequency analysis
  on time series data over multiple trials
 
  Use as
    [freq] = ft_freqanalysis(cfg, data)
 
  The input data should be organised in a structure as obtained from
  the FT_PREPROCESSING or the FT_MVARANALYSIS function. The configuration
  depends on the type of computation that you want to perform.
 
  The configuration should contain:
    cfg.method     = different methods of calculating the spectra
                     'mtmfft', analyses an entire spectrum for the entire data
                       length, implements multitaper frequency transformation
                     'mtmconvol', implements multitaper time-frequency
                       transformation based on multiplication in the frequency
                       domain.
                     'mtmwelch', performs frequency analysis using Welch's
                       averaged modified periodogram method of spectral
                       estimation.
                     'wavelet', implements wavelet time frequency
                       transformation (using Morlet wavelets) based on
                       multiplication in the frequency domain.
                     'tfr', implements wavelet time frequency transformation
                         (using Morlet wavelets) based on convolution in the
                         time domain.
                     'mvar', does a fourier transform on the coefficients of
                         an estimated multivariate autoregressive model,
                         obtained with FT_MVARANALYSIS. In this case, the
                         output will contain a spectral transfer matrix,
                         the cross-spectral density matrix, and the
                         covariance matrix of the innovatio noise.
 
                     OR, if you want to use the old implementation (not from
                       the specest module)
                       'mtmfft_old'
                       'mtmconvol_old'
                       'wltconvol_old'
    cfg.output     = 'pow'       return the power-spectra
                     'powandcsd' return the power and the cross-spectra
                     'fourier'   return the complex Fourier-spectra
    cfg.channel    = Nx1 cell-array with selection of channels (default = 'all'),
                       see FT_CHANNELSELECTION for details
    cfg.channelcmb = Mx2 cell-array with selection of channel pairs (default = {'all' 'all'}),
                       see FT_CHANNELCOMBINATION for details
    cfg.trials     = 'all' or a selection given as a 1xN vector (default = 'all')
    cfg.keeptrials = 'yes' or 'no', return individual trials or average (default = 'no')
    cfg.keeptapers = 'yes' or 'no', return individual tapers or average (default = 'no')
    cfg.pad        = number or 'maxperlen', length in seconds to which the
                       data can be padded out (default = 'maxperlen') The
                       padding will determine your spectral resolution. If
                       you want to compare spectra from data pieces of
                       different lengths, you should use the same cfg.pad
                       for both, in order to spectrally interpolate them to
                       the same spectral resolution.  Note that this will
                       run very slow if you specify cfg.pad as maxperlen
                       AND the number of samples turns out to have a large
                       prime factor sum. This is because the FFTs will then
                       be computed very inefficiently.
    cfg.polyremoval = number (default = 0), specifying the order of the
                       polynome which is fitted and subtracted from the
                       time domain data prior to the spectral analysis. For example, a
                       value of 1 corresponds to a linear trend. The default is a mean
                       subtraction, thus a value of 0. If no removal is requested,
                       specify -1.
                       see FT_PREPROC_POLYREMOVAL for details
 
 
   METHOD SPECIFIC OPTIONS AND DESCRIPTIONS
 
   MTMFFT
    MTMFFT performs frequency analysis on any time series
    trial data using the 'multitaper method' (MTM) based on discrete
    prolate spheroidal sequences (Slepian sequences) as tapers. Alternatively,
    you can use conventional tapers (e.g. Hanning).
    cfg.foilim     = [begin end], frequency band of interest
        OR
    cfg.foi        = vector 1 x numfoi, frequencies of interest
    cfg.tapsmofrq  = number, the amount of spectral smoothing through
                     multi-tapering. Note that 4 Hz smoothing means
                     plus-minus 4 Hz, i.e. a 8 Hz smoothing box.
    cfg.taper      = 'dpss', 'hanning' or many others, see WINDOW (default = 'dpss')
                      For cfg.output='powandcsd', you should specify the channel combinations
                      between which to compute the cross-spectra as cfg.channelcmb. Otherwise
                      you should specify only the channels in cfg.channel.
 
   MTMCONVOL
    MTMCONVOL performs time-frequency analysis on any time series trial data
    using the 'multitaper method' (MTM) based on Slepian sequences as tapers. Alternatively,
    you can use conventional tapers (e.g. Hanning).
    cfg.tapsmofrq  = vector 1 x numfoi, the amount of spectral smoothing through
                     multi-tapering. Note that 4 Hz smoothing means
                     plus-minus 4 Hz, i.e. a 8 Hz smoothing box.
    cfg.foilim     = [begin end], frequency band of interest
        OR
    cfg.foi        = vector 1 x numfoi, frequencies of interest
    cfg.taper      = 'dpss', 'hanning' or many others, see WINDOW (default = 'dpss')
                      For cfg.output='powandcsd', you should specify the channel combinations
                      between which to compute the cross-spectra as cfg.channelcmb. Otherwise
                      you should specify only the channels in cfg.channel.
    cfg.t_ftimwin  = vector 1 x numfoi, length of time window (in seconds)
    cfg.toi        = vector 1 x numtoi, the times on which the analysis windows
                     should be centered (in seconds)
 
   WAVELET
    WAVELET performs time-frequency analysis on any time series trial data
    using the 'wavelet method' based on Morlet wavelets. Using mulitplication
    in the frequency domain instead of convolution in the time domain.
    cfg.foi        = vector 1 x numfoi, frequencies of interest
        OR
    cfg.foilim     = [begin end], frequency band of interest
    cfg.toi        = vector 1 x numtoi, the times on which the analysis windows
                     should be centered (in seconds)
    cfg.width      = 'width' of the wavelet, determines the temporal and spectral
                     resolution of the analysis (default = 7)
                     constant, for a 'classical constant-Q' wavelet analysis
                     vector, defining a variable width for each frequency
    cfg.gwidth     = determines the length of the used wavelets in standard deviations
                     of the implicit Gaussian kernel and should be choosen
                     >= 3; (default = 3)
       The standard deviation in the frequency domain (sf) at frequency f0 is
       defined as: sf = f0/width
       The standard deviation in the temporal domain (st) at frequency f0 is
       defined as: st = width/f0 = 1/sf
 
 
   TFR
    TFR performs time-frequency analysis on any time series trial data
    using the 'wavelet method' based on Morlet wavelets. Using convolution
    in the time domain instead of multiplication in the frequency domain.
    cfg.foi        = vector 1 x numfoi, frequencies of interest
        OR
    cfg.foilim     = [begin end], frequency band of interest
    cfg.width      = 'width' of the wavelet, determines the temporal and spectral
                     resolution of the analysis (default = 7)
                     constant, for a 'classical constant-Q' wavelet analysis
                     vector, defining a variable width for each frequency
    cfg.gwidth     = determines the length of the used wavelets in standard deviations
                     of the implicit Gaussian kernel and should be choosen
                     >= 3; (default = 3)
 
 
 
  To facilitate data-handling and distributed computing with the peer-to-peer
  module, this function has the following options:
    cfg.inputfile   =  ...
    cfg.outputfile  =  ...
  If you specify one of these (or both) the input data will be read from a *.mat
  file on disk and/or the output data will be written to a *.mat file. These mat
  files should contain only a single variable, corresponding with the
  input/output structure.
 
  See also FT_FREQANALYSIS_OLD