


Multi-taper segmented, second spectrum (spectrum of the spectrum) for a continuous process
This routine computes the second spectrum by explicitly evaluating the
Fourier transform (since the spectrum is symmetric in frequency, it uses
a cosine transform)
Usage:
[SS,tau]=mtspectrum_of_spectrumc(data,win,tapers,params)
Input:
Note units have to be consistent. See chronux.m for more information.
data (single channel) -- required
win (duration of the segments) - required.
tapers (tapers used for the spectrum of spectrum computation) -
required in the form [TW K] - note that this is distinct from the
the tapers argument in params. The latter is used to compute the
spectrum itself.
params: structure with fields tapers, pad, Fs, fpass, err, trialave
- optional
tapers (precalculated tapers from dpss, or in the form [NW K] e.g [3 5]) -- optional. If not
specified, use [NW K]=[3 5]
pad (padding factor for the FFT) - optional. Defaults to 0.
e.g. For N = 500, if PAD = 0, we pad the FFT
to 512 points; if PAD = 2, we pad the FFT
to 2048 points, etc.
Fs (sampling frequency) - optional. Default 1.
fpass (frequency band to be used in the calculation in the form
[fmin fmax])- optional.
Default all frequencies between 0 and
Fs/2
Output:
SS (second spectrum in form frequency x segments x trials x channels
if segave=0; in the form frequency x trials x channels if segave=1)
tau (frequencies)

0001 function [SS,tau]=mtspectrum_of_spectrumc(data,win,tapers,params) 0002 % Multi-taper segmented, second spectrum (spectrum of the spectrum) for a continuous process 0003 % This routine computes the second spectrum by explicitly evaluating the 0004 % Fourier transform (since the spectrum is symmetric in frequency, it uses 0005 % a cosine transform) 0006 % 0007 % Usage: 0008 % 0009 % [SS,tau]=mtspectrum_of_spectrumc(data,win,tapers,params) 0010 % Input: 0011 % Note units have to be consistent. See chronux.m for more information. 0012 % data (single channel) -- required 0013 % win (duration of the segments) - required. 0014 % tapers (tapers used for the spectrum of spectrum computation) - 0015 % required in the form [TW K] - note that this is distinct from the 0016 % the tapers argument in params. The latter is used to compute the 0017 % spectrum itself. 0018 % params: structure with fields tapers, pad, Fs, fpass, err, trialave 0019 % - optional 0020 % tapers (precalculated tapers from dpss, or in the form [NW K] e.g [3 5]) -- optional. If not 0021 % specified, use [NW K]=[3 5] 0022 % pad (padding factor for the FFT) - optional. Defaults to 0. 0023 % e.g. For N = 500, if PAD = 0, we pad the FFT 0024 % to 512 points; if PAD = 2, we pad the FFT 0025 % to 2048 points, etc. 0026 % Fs (sampling frequency) - optional. Default 1. 0027 % fpass (frequency band to be used in the calculation in the form 0028 % [fmin fmax])- optional. 0029 % Default all frequencies between 0 and 0030 % Fs/2 0031 % Output: 0032 % SS (second spectrum in form frequency x segments x trials x channels 0033 % if segave=0; in the form frequency x trials x channels if segave=1) 0034 % tau (frequencies) 0035 if nargin < 3; error('Need data,segment duration and taper information'); end; 0036 if nargin < 4 ; params=[]; end; 0037 [tapers,pad,Fs,fpass,err,trialave,params]=getparams(params); 0038 [N,Ntr,NC]=size(data); 0039 if Ntr==1; error('cannot compute second spectrum with just one trial'); end; 0040 dt=1/Fs; % sampling interval 0041 T=N*dt; % length of data in seconds 0042 E=0:win:T-win; % fictitious event triggers 0043 datatmp=createdatamatc(data(:,1,1),E,Fs,[0 win]); % segmented data 0044 Ninseg=size(datatmp,1); % number of samples in segments 0045 nfft=2^(nextpow2(Ninseg)+pad); 0046 [f,findx]=getfgrid(Fs,nfft,fpass); 0047 NF=length(findx); 0048 S=zeros(NF,Ntr,NC); 0049 for nc=1:NC; 0050 for ntr=1:Ntr; 0051 datatmp=change_row_to_column(data(:,ntr,nc)); 0052 s=mtspectrumsegc(datatmp,win,params,1); 0053 S(:,ntr,nc)=s; 0054 end 0055 end; 0056 Sm=mean(S,2); 0057 tau=[0:NF-1]/max(f); 0058 cosinefunc=cos(2*pi*f'*tau); 0059 params.tapers=tapers; 0060 params.Fs=1/(f(2)-f(1)); 0061 params.fpass=[0 params.Fs/2]; 0062 for nc=1:NC; 0063 for ntr=1:Ntr; 0064 s=S(:,ntr,nc)./Sm(:,nc); 0065 s=log(s); 0066 % sflip=flipdim(s,1); 0067 % s=[sflip(1:NF-1);s]; 0068 % [ss,tau]=mtspectrumc(s,params); 0069 % SS(:,ntr,nc)=ss; 0070 s=repmat(s,[1 NF]).*cosinefunc; 0071 % subplot(221); plot(s(:,1)); 0072 % subplot(222); plot(s(:,10)); 0073 % subplot(223); plot(s(:,100)); 0074 % subplot(224); plot(s(:,120)); 0075 % pause 0076 s=trapz(f,s,1)'; 0077 s=s.*conj(s); 0078 % plot(tau,s) 0079 % pause 0080 SS(:,ntr,nc)=s; 0081 end 0082 end; 0083 SS=mean(SS,2);