function outsig = sig_transposedtone(siglen,fc,fm,fs,varargin)
%SIG_TRANSPOSEDTONE Transposed tone test stimuli
% Usage: ts = sig_transposedtone(fc,fm,dur,fs);
%
% Input parameters:
% siglen : Length of signal
% fc : Vector of carrier frequencies (Hz)
% fm : Vector of modulation frequencies (Hz)
% fs : Sampling frequency (Hz)
%
% Output parameters:
% outsig : transposed tone (column vector)
%
% SIG_TRANSPOSEDTONE(siglen,fc,fm,dur,fs) generates a transposed tone test
% stimuli as defined in Kolrausch et. al (1997).
%
% By default, the output is normalized to have an RMS value of 1, but this
% can be changed by passing any of the flags from the normalize function.
%
% Some example parameters as used in a study by Santurette:
%
% siglen = 44100;
% fc = 5000;
% fm = 435;
% fs = 44100;
% outsig = sig_transposedtone(fc,fm,dur,fs);
%
% References:
% A. Kohlrausch, R. Fassel, M. Heijden, R. Kortekaas, S. Par, A. Oxenham,
% and D. Puschel. Detection of tones in low-noise noise: Further evidence
% for the role of envelope fluctuations. Acta Acustica united with
% Acoustica, 83(4):659--669, 1997.
%
% A. Oxenham, J. Bernstein, and H. Penagos. Correct tonotopic
% representation is necessary for complex pitch perception. Proceedings
% of the National Academy of Sciences, 101(5):1421--1425, 2004.
%
%
% Url: http://amtoolbox.org/amt-1.2.0/doc/signals/sig_transposedtone.php
% Copyright (C) 2009-2022 Piotr Majdak, Clara Hollomey, and the AMT team.
% This file is part of Auditory Modeling Toolbox (AMT) version 1.2.0
%
% 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: Sébastien Santurette 2009
if nargin<4
error('Too few input parameters.');
end;
definput.import={'normalize'};
definput.importdefaults={'rms'};
[flags,keyvals]=ltfatarghelper({},definput,varargin);
% time vector
t = (0:siglen-1)/fs;
% number of tones
n = length(fc);
outsig = zeros(siglen,1);
for ii = 1:n
% carrier tone
carrier = cos(2*pi*fc(ii)*t);
% "modulator"
hrsine = sin(2*pi*fm(ii)*t);
% half-wave rectify the modulator
hrsine = max(0,hrsine);
% Compute coefficients for low-pass filtering
fcuth = .2*fc(ii)/(fs/2);
[b,a] = butter(4,fcuth,'low');
% Low-pass filter the modulator
hrsine = filter(b,a,hrsine);
% Add the carrier*modulator to the transposed tone
outsig = outsig+(carrier.*hrsine)';
end;
outsig=normalize(outsig,flags.norm);