function s=waveform(wtype,f,d,sr);
% waveforms of a given type, frequency, duration and sample rate;
t= 0:1/sr:d;
if (wtype==1)
    s=sin(2*pi*f*t);    % sinewave
elseif (wtype==2)
    s=sin(2*pi*f*t);    % square wave
    s=2*(s > 0) - 1;
elseif (wtype==3)
    s=zeros(1,length(t));   % pulse train
    s(1:fix(sr/f):length(s))=1;
end
sound(s,sr);