NOISE - Stochastic noise generator

function outsig = noise(siglen,varargin)
% NOISE  Stochastic noise generator
%   Usage: outsig = noise(siglen,nsigs,type);
%
%   Input parameters:
%       siglen    : Length of the noise (samples)
%       nsigs     : Number of signals (default is 1)
%       type      : type of noise. See below.
%
%   Output parameters:
%       outsig    : siglen xnsigs signal vector
%
%   NOISE(siglen,nsigs) generates nsigs channels containing white noise
%   of the given type with the length of siglen. The signals are arranged as
%   columns in the output. If only siglen is given, a column vector is
%   returned.
%
%   NOISE takes the following optional parameters:
%
%     'white'  Generate white (gaussian) noise. This is the default.
%
%     'pink'   Generate pink noise.
%
%     'brown'  Generate brown noise.
%
%     'red'    This is the same as brown noise.     
%
%   By default, the noise is normalized to have a unit energy, but this can
%   be changed by passing a flag to SETNORM.
%
%   Examples:
%   ---------
%    
%   White noise in the time-frequency domain:
%
%     sgram(noise(5000,'white'),'dynrange',70);
%
%   Pink noise in the time-frequency domain:
%
%     sgram(noise(5000,'pink'),'dynrange',70);
%
%   Brown/red noise in the time-frequency domain:
%
%     sgram(noise(5000,'brown'),'dynrange',70);
% 
%   See also: setnorm
%
%   Url: http://ltfat.github.io/doc/signals/noise.html

% Copyright (C) 2005-2023 Peter L. Soendergaard <peter@sonderport.dk> and others.
% This file is part of LTFAT version 2.6.0
%
% This program is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
%
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with this program.  If not, see <http://www.gnu.org/licenses/>.

%   AUTHOR: Hagen Wierstorf and Peter L. Søndergaard.



% ------ Checking of input parameter -------------------------------------

if nargin<1
  error('%s: Too few input parameters.',upper(mfilename));
end;

if ~isnumeric(siglen) || ~isscalar(siglen) || siglen<=0
    error('%s: siglen has to be a positive scalar.',upper(mfilename));
end

definput.import={'setnorm'};
definput.importdefaults={'2'};
definput.flags.noisetype={'white','pink','brown','red'};
definput.keyvals.nsigs=1;
[flags,kv,nsigs]  = ltfatarghelper({'nsigs'},definput,varargin);

if flags.do_white
  outsig=randn(siglen,nsigs);
end;

if flags.do_brown || flags.do_red
  outsig=cumsum(randn(siglen,nsigs));
end;

if flags.do_pink
  % --- Handle trivial condition

  if siglen==1
    outsig=ones(1,nsigs);
    return;
  end;

  % ------ Computation -----------------------------------------------------
  fmax = floor(siglen/2)-1;
  f = (2:(fmax+1)).';
  % 1/f amplitude factor
  a = 1./sqrt(f);
  % Random phase
  p = randn(fmax,nsigs) + i*randn(fmax,nsigs);
  sig = bsxfun(@times,a,p);

  outsig = ifftreal([ones(1,nsigs); sig; 1/(fmax+2)*ones(1,nsigs)],siglen);

end;

outsig=setnorm(outsig,flags.norm);