bleeck@4: function sig=reduce_tilt(sig,options)
bleeck@4: 
bleeck@4: 
bleeck@4: plot_switch=1;
bleeck@4: 
bleeck@4: lowpassfactor=100;	% relationship between Samplefrequency and lowpassfrequency
bleeck@4: 
bleeck@4: % shift all values that are zero at the beginning to the first
bleeck@4: % positive value. This makes the lowpass continuous for high
bleeck@4: % frequencies
bleeck@4: sr=getsr(sig);
bleeck@4: stip=getvalues(sig);
bleeck@4: 
bleeck@4: indx=find(stip>0);
bleeck@4: if ~isempty(indx)
bleeck@4: 	first_non_zero=stip(indx(1));
bleeck@4: 	stip(1:indx(1))=first_non_zero;
bleeck@4: 	stip=[ones(200,1)*first_non_zero;stip];
bleeck@4: end
bleeck@4: s=signal(stip,sr);
bleeck@4: s=reverse(s);
bleeck@4: s2=lowpass(s,sr/lowpassfactor);
bleeck@4: diff=s-s2;
bleeck@4: 
bleeck@4: % s2=getpart(s2,0,getlength(sig));
bleeck@4: 
bleeck@4: 
bleeck@4: if plot_switch
bleeck@4: 	figure(4)
bleeck@4: 	clf
bleeck@4: 	plot(s);
bleeck@4: 	hold on
bleeck@4: 	plot(s2,'r');
bleeck@4: 	plot(diff,'g')
bleeck@4: 	axis([0 getnrpoints(sig) min(diff)-10 max(sig)+10]);
bleeck@4: end
bleeck@4: 
bleeck@4: diff=getpart(diff,0,getlength(sig));
bleeck@4: diff=reverse(diff);
bleeck@4: 
bleeck@4: 
bleeck@4: % return value
bleeck@4: sig=diff;