view toolboxes/MIRtoolbox1.3.2/AuditoryToolbox/spectrogram.m @ 0:e9a9cd732c1e tip

first hg version after svn

function [array,raw] = spectrogram(wave,segsize,nlap,ntrans);
%function array = spectrogram(wave,segsize,nlap,ntrans);
% defaults spectrogram(wave,128,8,4)
% nlap is number of hamming windows overlapping a point;
% ntrans is factor by which transform is bigger than segment;
% returns a spectrogram 'array' with fourth root of power,
% filter smoothed and formatted for display.

% Added option to return raw spectrogram.... Malcolm 5/26/95
% Added code so that input could be any direction ... Malcolm 5/26/95
% (c) 1998 Interval Research Corporation  

if nargin < 4; ntrans=4; end
if nargin < 3; nlap=8; end
if nargin < 2; segsize=128; end

[r c] = size(wave);
if (r < c)
	wave = filter([1 -0.95],[1],wave');
else
	wave = filter([1 -0.95],[1],wave);
end

s = length(wave);
nsegs = floor(s/(segsize/nlap))-nlap+1;
array = zeros(ntrans/2*segsize,nsegs);
window = 0.54-0.46*cos(2*pi/(segsize+1)*(1:segsize)');
for i = 1:nsegs
 seg = zeros(ntrans*segsize,1); % leave half full of zeroes
 seg(1:segsize) = ...
	 window.*wave(((i-1)*segsize/nlap+1):((i+nlap-1)*segsize/nlap));
 seg = abs(fft(seg));
						% reverse for image display
 array(:,i) = seg(((ntrans/2*segsize)+1):(ntrans*segsize));
end

if nargout > 1
	raw = array;
end

array = array .* array;			% back into power domain for smoothing

for i=1:nsegs    % smooth the spectral slices
 array(:,i) = filter([.2 1 .2],[1],array(:,i));
end

for i=1:ntrans/2*segsize    % smooth the channels
 array(i,:) = filter([.2 1 .2],[1],array(i,:));
end

% compress with square root of amplitude (fourth root of power)
off = 0.0001*max(max(array));      	% low end stabilization offset,
array = (off+array).^0.25-off^0.25; 	% better than a threshold hack!
array = 255/max(max(array))*array;