function [outsig, fc, mfc] = dau1997_preproc(insig, fs, varargin);
%dau1997_preproc   Auditory model from Dau et. al. 1997
%   Usage: [outsig, fc] = dau1997_preproc(insig,fs);
%          [outsig, fc] = dau1997_preproc(insig,fs,...);
%
%   Input parameters:
%     insig  : input acoustic signal.
%     fs     : sampling rate.
%  
%   DAU1997_PREPROC(insig,fs) computes the internal representation of the
%   signal insig sampled with a frequency of fs Hz.
%  
%   [outsig,fc,mfc]=DAU1997_PREPROC(...) additionally returns the center
%   frequencies of the filter bank and the center frequencies of the
%   modulation filterbank.
%  
%   The model consists of the following stages:
%   
%   1) a gammatone filter bank with 1-erb spaced filtes.
%
%   2) an envelope extraction stage done by half-wave rectification
%      followed by low-pass filtering to 1000 Hz.
%
%   3) an adaptation stage modelling nerve adaptation by a cascade of 5
%      loops.
%
%   4) a modulation filterbank
%
%   Any of the optinal parameters for AUDITORYFILTERBANK,
%   IHCENVELOPE and ADAPTLOOP may be optionally specified for this
%   function. They will be passed to the corresponding functions.
%
%   See also: auditoryfilterbank, ihcenvelope, adaptloop, modfilterbank
%
%   Url: http://amtoolbox.sourceforge.net/amt-0.10.0/doc/modelstages/dau1997_preproc.php

% Copyright (C) 2009-2020 Piotr Majdak and the AMT team.
% This file is part of Auditory Modeling Toolbox (AMT) version 0.10.0
%
% 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/>.

%   References: dau1997mapI dau1997mapII

%   AUTHOR : Torsten Dau, Morten Løve Jepsen, Peter L. Søndergaard. 
%     Modifications by Alejandro Osses.

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

if nargin<2
  error('%s: Too few input arguments.',upper(mfilename));
end;

if ~isnumeric(insig) 
  error('%s: insig must be numeric.',upper(mfilename));
end;

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

definput.import={'auditoryfilterbank','ihcenvelope','adaptloop','modfilterbank'};
definput.importdefaults={'gtf_dau', 'ihc_dau', 'adt_dau','mfb_jepsen2008'}; 
                    % The flag 'mfb_dau1997' would be exactly as in day1997mapI
definput.keyvals.subfs=[];

[flags,keyvals]  = ltfatarghelper({'flow','fhigh'},definput,varargin);

% ------ do the computation -------------------------

if flags.do_outerear
  hp_fir = headphonefilter(fs);% Getting the filter coefficients at fs
  N = ceil(length(hp_fir)/2);  % group delay for a FIR filter of order length(hp_fir)
  M = 1; % assumes insig is monaural
  insig = [insig; zeros(N,M)]; % group delay compensation: step 1 of 2. 
  insig = filter(hp_fir,1,insig); % filtering
  insig = insig(N+1:end,1:M); % group delay compensation: step 2 of 2
end

if flags.do_middleear || flags.do_jepsenmiddleear
  if flags.do_middleear
      filtertype = 'lopezpoveda';
  elseif flags.do_jepsenmiddleear
      filtertype = 'jepsenmiddleear';
  end
  me_fir = middleearfilter(fs,filtertype);
  N = ceil(length(me_fir)/2); % group delay for a FIR filter of order length(me_fir)
  M = 1; % assumes insig is monaural
  insig = [insig; zeros(N,M)]; % group delay compensation: step 1 of 2.
  insig = filter(me_fir,1,insig); % filtering
  insig = insig(N+1:end,1:M); % group delay compensation: step 2 of 2. 
  me_gain_TF = max( 20*log10(abs(freqz(me_fir,1,8192))) ); % max of the filter response
  insig = gaindb(insig,-me_gain_TF); % if me_fir is a non-unit gain filter, 
                                     % the gain of the FIR filter is compensated.
end

% Apply the auditory filterbank
[outsig, fc] = auditoryfilterbank(insig,fs,'argimport',flags,keyvals);

% 'haircell' envelope extraction
outsig = ihcenvelope(outsig,fs,'argimport',flags,keyvals);

% non-linear adaptation loops
outsig = adaptloop(outsig,fs,'argimport',flags,keyvals);

%% Downsampling (of the internal representations)
% Apply final resampling to avoid excessive data
if ~isempty(keyvals.subfs)
    % In case of downsampling:
    outsig = fftresample(outsig,round(length(outsig)/fs*keyvals.subfs));
    subfs = keyvals.subfs;
else
    % In case of no-resampling:
    subfs = fs;
end

% Modulation filterbank
[outsig,mfc] = modfilterbank(outsig,subfs,fc,'argimport',flags,keyvals);