```
function [fcs, powers, varargout] = ewert2000(data,fs)
%EWERT2000 - Modulation filterbank (based on EPSM)
% Usage: [fcs,powers] = ewert2000(data,fs)
%
% Input parameters:
% data : Frequencies of the data, starting from f = 0
%
% data : Powerspectrum data to be filtered.
%
% fcs : Centre frequencies of the filters
%
% powers : Integrated power at the output of each filter
%
% Wcf : Matrix containing the frequency-domain squared transfer function
%
% fig : flag for plotting fitler transferfunctions 1 = yes, 0 = no
% plotting
%
% Output parameters:
% fcs : centre frequencies of the filters
%
% powers: filter coefficients
%
% [fcs powers] = EWERT2000(data,fig,fs) computes the
% EPSM-filterbank as presented by Ewert & Dau 2000, without the additional
% lowpass filter with a cut-off at 150 Hz. This implementation consists of
% a lowpass filter with a cutoff at 1 Hz, in parallel with 6 bandpass
% filters with octave spacing. the Center-frequencies of the bandpass
% filters are lower than the original from Ewert & Dau (2000). In each of
% the filters data is integrated within the pass-band of the filter to
% give the power within that filter.
%
% See also: demo_ewert2000
%
% References:
% S. Ewert and T. Dau. Characterizing frequency selectivity for envelope
% fluctuations. J. Acoust. Soc. Am., 108(3):1181--1196, 2000.
%
%
% Url: http://amtoolbox.org/amt-1.1.0/doc/models/ewert2000.php
% Copyright (C) 2009-2021 Piotr Majdak, Clara Hollomey, and the AMT team.
% This file is part of Auditory Modeling Toolbox (AMT) version 1.1.0
%
% 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/>.
% #StatusDoc: Good
% #StatusCode: Perfect
% #Verification: Unknown
% #Author: Søren Jørgensen
% #Author: Clara Hollomey (moved plot to demo)
if mod(length(data),2) == 0
%number is even
data = data(1:end-1);
else
%number is odd
end
Q = 1;
N = length(data);
X = fft(data);
X_mag = abs(X) ;
X_power = X_mag.^2/N ;% power spectrum.
X_power_pos = X_power(1:fix(N/2)+1) ;
%take positive frequencies only and mulitply by two-squared to get the same total energy
X_power_pos(2:end) = X_power_pos(2:end).* (2) ;
pos_freqs= linspace(0,fs/2,length(X_power_pos));
freqs = [pos_freqs -1*fliplr(pos_freqs(2:end))];
%band center frequencies
fcs=[ 2 4 8 16 32 64 ];
% Initialize transfer function
TFs = zeros(length(fcs),length(freqs));
% Calculating frequency-dmoain transferfunction for each center frequency:
for k = 1:length(fcs)
TFs(k+1,2:end) = 1./(1+ (1j*Q*(freqs(2:end)./fcs(k) - fcs(k)./freqs(2:end)))); % p287 Hambley.
end
% squared filter magnitude transfer functions
Wcf = (abs(TFs)).^2;
% cutoff frequency of lowpassfilter:
fcut = 1;
% order:
n = 3;
% Lowpass filter squared transfer function: third order butterworth filter
% TF from: http://en.wikipedia.org/wiki/Butterworth_filter
Wcf(1,:) = 1./(1+((2*pi*freqs/(2*pi*fcut)).^(2*n)));
TFs(1,:) = sqrt(Wcf(1,:));
% initialize output product:
Vout = zeros(length(fcs),length(pos_freqs));
powers = zeros(1,7);
% ------------ DC-power, --------------------------
% %here devided by two such that a fully modulated tone has an AC-power of 1.
DC_power = X_power_pos(1)/ N /2;
% ------------------------------------------------
for k = 1:size(Wcf,1)
Vout(k,:) = X_power_pos.*Wcf(k,1:floor(end/2)+1);
% Integration estimated as a sum from f > 0
% integrate envelope power in the
% passband of the filter. Index goes from 2:end since
powers(k) = sum(Vout(k,2:end))/ N / DC_power;
% integration is for f>0
end
fcs = [1 fcs];
if nargout >= 3
varargout{1} = TFs;
if nargout >= 4
varargout{2} = freqs;
end
end
```