function outsig = itdildsin(fc,itd,ild,fs)
%ITDILDSIN Generate a sinusoid with a interaural time difference
%   Usage: outsig = itdildsin(fc,itd,ild,fs)
%
%   Input parameters:
%       fc      : carrier frequency of the sinusoid (Hz)
%       itd     : ITD of the left signal, this can be positive or negative (ms)
%       ild     : ILD of the right signal, this can be positive or negative (dB)
%       fs      : sampling rate (Hz)
%
%   Output parameters:
%       outsig  : two channel 1 s long sinusoid
%
%   `itdildsin(fc,itd,ild,fs)` generates a sinusoid with a interaural time 
%   difference of *itd*, a interaural level difference of *ild* and a frequency of 
%   *fc*.
%
%   The output is scaled to have a maximum value of 1-eps.  
%
%   References: moore2003introduction

% AUTHOR: Hagen Wierstorf


% ------ Checking of input parameters ---------

error(nargchk(4,4,nargin));

if ~isnumeric(fc) || ~isscalar(fc) || fc<0
    error('%s: f must be a positive scalar.',upper(mfilename));
end

if ~isnumeric(itd) || ~isscalar(itd)
    error('%s: itd must be a scalar.',upper(mfilename));
end

if ~isnumeric(ild) || ~isscalar(ild)
    error('%s: ild must be a scalar.',upper(mfilename));
end

if ~isnumeric(fs) || ~isscalar(fs) || fs<=0
    error('%s: fs must be a positive scalar!',upper(mfilename));
end


% ------ Computation --------------------------

% Create a one second time 
t = (1:fs)/fs;
% Right signal
sigr = sin(2*pi*fc.*t);
% Time shift in samples
itdsamples = ceil(fs * abs(itd)/1000);
% Left signal with ITD shift
sigl = [zeros(1,itdsamples) sin(2*pi*fc.*t(1:end-itdsamples))];
% Combine left and right signal to outsig
% Check if we have a positive or negative ITD and switch left and right signal
% for negative ITD
if itd<0
    % Apply ILD
    sigl = gaindb(sigl,ild);
    outsig = [sigr' sigl'];
else
    % Apply ILD
    sigr = gaindb(sigr,ild);
    outsig = [sigl' sigr'];
end
% Scale outsig
outsig = outsig / (max(abs(outsig(:)))+eps);