function z=addnoise(y,n);
% ADDNOISE: Adds tones to a sound (so that you can try to remove
%   the tone afterwards).
%
%   y=ADDNOISE(y,1) adds a single tone to y.
%   y=ADDNOISE(y,2) adds another single tone to y.
%   y=ADDNOISE(y,3) adds three tones to y.
%
% Example:
%   y=auread("bart1.au");   % load in some sound
%   sound(y);               % play the sound
%   z=fft(y);               % compute Fourier transform
%   plot(abs(z));           % look at the spectrum
%
%   y=addnoise(y,1);        % now add some noise
%   sound(y);               % play that
%   z=fft(y);               % recompute Fourier transform
%   plot(abs(z));           % look at new spectrum

% Authors:
%   Karl Bauer and Alexander Perlis
%   SouthWest Regional Institute in the Mathematical Sciences
%   c/o Department of Mathematics
%   The University of Arizona
%   Tucson, AZ 85721
%   bauer@math.arizona.edu, aprl@math.arizona.edu
%
% Obtain the latest version of this software from:
%   http://www.math.arizona.edu/~rims/workshops/fourier/softwareMATLAB
%
% Bugs/problems/ideas:
%   None.
%
% Change history:
%   Dec 1997  Originally three separate programs by Karl Bauer
%   Dec 1997  Combined into a single program by Alexander Perlis

%----------------------------------------------------------------------------


L=length(y);
t=1:L;
t=t/8192;
switch n,
  case 1,
    f=8192/4, z=y+cos(2*pi*f*t);
  case 2,
    f=8192/3, z=y+cos(2*pi*f*t);
  case 3,
    f1=1235, f2=2476, f3=3431;
    z=y+cos(2*pi*f1*t)'+cos(2*pi*f2*t)'+cos(2*pi*f3*t)';
end;

% [eof]