nt_sgram

[s,f,t]=nt_sgram(x,window,noverlap,nfft,sr,flags) - spectrogram

 Without output arguments: plot cubic root of power spectrogram.
 With output arguments: return power spectrogram.
  s: spectrogram matrix (frequency X time)
  f: array of frequencies
  t: array of times

  x: data (if multidimensional, power is averaged over higher dimensions)
  window: size of hamming window in samples, if vector, shape of window
  noverlap: frame period in samples
  nfft: number of points in FFT (default 2^nextpow2(window size))
  sr: sampling rate.
  flags: 'nomean': remove mean of each window

  NoiseTools

0001 function [s,f,t]=nt_sgram(x,window,noverlap,nfft,sr,flags)
0002 %[s,f,t]=nt_sgram(x,window,noverlap,nfft,sr,flags) - spectrogram
0003 %
0004 % Without output arguments: plot cubic root of power spectrogram.
0005 % With output arguments: return power spectrogram.
0006 %  s: spectrogram matrix (frequency X time)
0007 %  f: array of frequencies
0008 %  t: array of times
0009 %
0010 %  x: data (if multidimensional, power is averaged over higher dimensions)
0011 %  window: size of hamming window in samples, if vector, shape of window
0012 %  noverlap: frame period in samples
0013 %  nfft: number of points in FFT (default 2^nextpow2(window size))
0014 %  sr: sampling rate.
0015 %  flags: 'nomean': remove mean of each window
0016 %
0017 %  NoiseTools
0018 nt_greetings;
0019 
0020 if nargin<1; error('!'); end
0021 if nargin<2; window=[]; end
0022 if nargin<3; noverlap=[]; end
0023 if nargin<4; nfft=[]; end
0024 if nargin<5; sr=[]; end
0025 if nargin<6; flags=[]; end
0026 
0027 if isempty(window)
0028     window=2^nextpow2(round(size(x,1)/8));
0029 end
0030 window=window(:);
0031 if numel(window)==1;
0032     window=hanning(window);
0033 end
0034 if isempty(noverlap)
0035     noverlap=floor(numel(window)/2);
0036 end
0037 if isempty(nfft)
0038     nfft=2^nextpow2(numel(window));
0039 end
0040 if isempty(sr)
0041     sr=1;
0042 end
0043 
0044 
0045 x=reshape(x,[size(x,1), prod(size(x))/size(x,1)]); % fold all higher dimensions
0046 
0047 nframes=floor( (size(x,1)-numel(window))/noverlap )  +  1;
0048 if nframes<1; error('data too short for window size'); end
0049 
0050 s=zeros(nfft/2+1,nframes);
0051 
0052 for k=1:nframes
0053     start=(k-1)*noverlap;
0054     xx=nt_vecmult(x(start+1:start+size(window),:),window); 
0055     if ~isempty(flags) & strcmp(flags,'demean');
0056         xx=nt_demean(xx);
0057     end
0058     XX=abs(fft(xx,nfft)).^2;
0059     s(:,k)=sum(XX(1:(nfft/2+1),:),2);
0060 end
0061 
0062 f=(0:nfft/2)*sr/nfft;
0063 t= (numel(window)/2 + (0:nframes-1)*noverlap) / sr;
0064 
0065 
0066 
0067 if nargout==0;
0068     ss=s.^(1/5);
0069     %ss=ss-repmat(mean(ss,2),1,size(ss,2));
0070 
0071     %nt_imagescc(ss);
0072     imagesc(ss);
0073     ytick=niceticks(sr/2);
0074     set(gca,'ytick',1+ytick*nfft/sr, 'yticklabel',num2str(ytick'));
0075     ylabel('Hz');
0076     xtick=niceticks(size(x,1)/sr);
0077     set(gca,'xtick',1+xtick/noverlap*sr - nfft/2/noverlap, 'xticklabel',num2str(xtick'));
0078     xlabel('s');
0079     set(gca,'tickdir','out')
0080     s=[];t=[];f=[];
0081     axis xy
0082 end
0083 
0084