generateNoise.m

function [n_] = generateNoise( x, level, type, add )
% Generates basic noise at a given level with the option to be additive
% 
% Syntax:	[n_] = GENERATENOISE( x, level, type, add ) Pass the signal, x, level
% and type of noise to the function and n_ will be the resulting noise.
% Alternatively you can specify whether to add the noise to the input
% signal and return the sum of the two using the 'add' argument.
% 
% Inputs: 
% 	x - The input signal to base the level of generated noise on. Or
% 	alternatively add the noise to.
% 	level - The noise in dB relative to the input signal
% 	type - The type of noise to add (e.g. 'WGN' for White Gaussian Noise)
%   add - true if input is added to noise, false (default) to return just the noise
% 
% Outputs: 
% 	n_ - The generated noise signal
% 
%
% Author: Jacob Donley
% University of Wollongong
% Email: jrd089@uowmail.edu.au
% Copyright: Jacob Donley 2017
% Date: 21 August 2015 
% Revision: 0.1
% 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

if nargin < 3
    type = 'WGN'; % White Gaussian Noise
end
if nargin < 4
    add = false;
end

% Maximum value in input signal
max_val =  max( abs( x(:) ) );

% Level in magnitude
level_mag = db2mag(level);

% Seed random number generator based on the current date/time
rng('shuffle');

if strcmp(type,'UWN') % Uniform White Noise
   
    noise_ = rand( size(x) ) * 2 - 1; % UWN: -1 to 1
    if ~add
        x = 0;
    end
    n_ = x + max_val * noise_ * level_mag;
    
elseif strcmp(type,'WGN') % White Gaussian Noise
    
    noise_ = randn( size(x) ); % WGN
    noise_ = noise_ / sqrt(bandpower(noise_)); %Normalise 
    if ~add
        x = 0;
    end
    n_ = x + max_val * noise_ * level_mag;
    
else
    error('''type'' argument for noise not supported');
end

end