dan@0: function [features,F,M] = lpc2spec(lpcas, nout)
dan@0: % [features,F,M] = lpc2spec(lpcas,nout)
dan@0: %    Convert LPC coeffs back into spectra
dan@0: %    nout is number of freq channels, default 17 (i.e. for 8 kHz)
dan@0: % 2003-04-11 dpwe@ee.columbia.edu  part of rastamat
dan@0: 
dan@0: if nargin < 2
dan@0:   nout = 17;
dan@0: end
dan@0: 
dan@0: [rows, cols] = size(lpcas);
dan@0: order = rows - 1;
dan@0: 
dan@0: gg = lpcas(1,:);
dan@0: aa = lpcas./repmat(gg,rows,1);
dan@0: 
dan@0: % Calculate the actual z-plane polyvals: nout points around unit circle
dan@0: zz = exp((-j*[0:(nout-1)]'*pi/(nout-1))*[0:order]);
dan@0: 
dan@0: % Actual polyvals, in power (mag^2)
dan@0: features =  ((1./abs(zz*aa)).^2)./repmat(gg,nout,1);
dan@0: 
dan@0: F = zeros(cols, floor(rows/2));
dan@0: M = F;
dan@0: 
dan@0: for c = 1:cols;
dan@0:   aaa = aa(:,c);
dan@0:   rr = roots(aaa');
dan@0:   ff = angle(rr');
dan@0: %  size(ff)
dan@0: %  size(aaa)
dan@0:   zz = exp(j*ff'*[0:(length(aaa)-1)]);
dan@0:   mags = sqrt(((1./abs(zz*aaa)).^2)/gg(c))';
dan@0:   
dan@0:   [dummy, ix] = sort(ff);
dan@0:   keep = ff(ix) > 0;
dan@0:   ix = ix(keep);
dan@0:   F(c,1:length(ix)) = ff(ix);
dan@0:   M(c,1:length(ix)) = mags(ix);
dan@0: end