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1 % pic = CorrelogramFrame(data, picWidth, start, winLen)
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2 % Compute one frame of a correlogram. The input data is a
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3 % two-dimensional array of cochlear data, each row representing
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4 % firing probabilities from one cochlear channel. The output
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5 % picture is a two dimensional array of width "picWidth".
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6 %
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7 % The correlogram is computed with autocorrelation using
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8 % data from the input array. For each channel, the data from
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9 % is extracted starting at column "start" and extending for
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10 % "winLength" time steps.
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11
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12 % (c) 1998 Interval Research Corporation
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13
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14 function pic = CorrelogramFrame(data, picWidth, start, winLen)
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15
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16 if nargin < 2
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17 disp('Syntax: pic=CorrelogramFrame(data, picWidth[, start, len])');
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18 return
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19 end
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20
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21 if nargin < 3
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22 start = 1;
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23 end
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24
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25 if nargin < 4
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26 [channels, winLen] = size(data);
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27 end
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28
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29 [channels, dataLen] = size(data);
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30 start = max(1, start);
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31 last = min(dataLen, start+winLen-1);
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32
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33 pic = zeros(channels, picWidth);
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34 fftSize = 2^(nextpow2(max(picWidth, winLen))+1);
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35 % disp(['CorrelogramFrame fftSize is ' int2str(fftSize)]);
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36
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37 a = .54;
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38 b = -.46;
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39 wr = sqrt(64/256);
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40 phi = pi/winLen;
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41 ws = 2*wr/sqrt(4*a*a+2*b*b)*(a + b*cos(2*pi*(0:winLen-1)/winLen + phi));
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42
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43 for i=1:channels
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44 f = zeros(1, fftSize);
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45 % d = zeros(1, winLen);
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46 % d(1:(last-start+1)) = data(i,start:last) .* ws(1:(last-start+1));
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47 % f(1:(winLen/2)) = d(winLen/2+1:winLen);
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48 % f(fftSize-(winLen/2)+1:fftSize) = d(1:min(length(d),winLen/2));
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49 f(1:(last-start+1)) = data(i,start:last) .* ws(1:(last-start+1));
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50 f = fft(f);
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51 f = ifft(f.*conj(f));
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52 pic(i,:) = real(f(1:picWidth));
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53 if pic(i,1) > pic(i,2) & pic(i,1) > pic(i,3)
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54 pic(i,:) = pic(i,:)/sqrt(pic(i,1));
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55 else
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56 pic(i,:) = zeros(1,picWidth);
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57 end
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58 end
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