decimation.m

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function [DFlags, DTonal_list, DNon_tonal_list] = Decimation(Tonal_list, ...
												  Non_tonal_list, Flags)
%
%   Authors: Fabien A.P. Petitcolas ([e-mail])
%            Teddy Furon ([e-mail])
%
%   Corrections:
%            Michael Arnold ([e-mail])
%            Fraunhofer Institute for Computer Graphics (IGD)     
% 
%   References: 
%    [1] Information technology -- Coding of moving pictures and associated 
%        audio for digital storage media at up to 1,5 Mbits/s -- Part3: audio. 
%        British standard. BSI, London. October 1993.Implementation of 
%        ISO/IEC 11172-3:1993. BSI, London. First edition 1993-08-01. 
%
%   Legal notice: 
%    This computer program is based on ISO/IEC 11172-3:1993, Information 
%    technology -- Coding of moving pictures and associated audio for digital 
%    storage media at up to about 1,5 Mbit/s -- Part 3: Audio, with the 
%    permission of ISO. Copies of this standards can be purchased from the 
%    British Standards Institution, 389 Chiswick High Road, GB-London W4 4AL,  
%    Telephone:+ 44 181 996 90 00, Telefax:+ 44 181 996 74 00 or from ISO, 
%    postal box 56, CH-1211 Geneva 20, Telephone [phone], Telefax 
%    [phone]. Copyright remains with ISO. 
%----------------------------------------------------------------------------
%
% [DFlags, DTonal_list, DNon_tonal_list]= ...
%			            Decimation(Tonal_list, Non_tonal_list, Flags)
%
%   Components which are below the auditory threshold OR are less than one 
%   half of a critical band width from a neighbouring component are
%   eliminated [1, pp. 113].
%
% -- INPUT --
% Flags: Vector of size FFT_SIZE/2 containing the markers TONAL or NON_TONAL. 
%
% Tonal_list: Matrix with two columns for the TONAL components. The first
% column are the frequency indexes (INDEX) in linear scale, the second one
% is the sound pressure level (SPL) [dB].
%
% Non_tonal_list: Matrix with two columns for the NON_TONAL components. The
% meaning of the columns is the same as in the Tonal_list case.
%
% -- OUTPUT --
% DFlags: Vector of size FFT_SIZE/2 containing the decimated markers TONAL or
% NON_TONAL.
%
% DTonal_list: Matrix with two columns for the decimated TONAL components. The
% meaning of the columns is the same as in the Tonal_list case. 
%
% DNon_tonal_list: Matrix with two columns for the decimated NON_TONAL
% components. The meaning of the columns is the same as in the Tonal_list case.
% -------------
%
%   See also Find_tonal_components
%---------------------------------------------------------------------------- 

global SPL INDEX ATH IRRELEVANT BARK Map TH
% Preset decimated Flags
DFlags = Flags; 

% Tonal or non-tonal components are not considered if lower than the absolute
% threshold of hearing found in TH(:, ATH). pp. 113 Step 5a 

% -- Non tonal case --
% Preset decimated non tonal list
DNon_tonal_list = Non_tonal_list; 

if not(isempty(Non_tonal_list))
  % Map linear frequency index to non-linear to index absolute threshold in
  % table TH.
  K = Non_tonal_list(:, SPL) < TH(Map(Non_tonal_list(:, INDEX)), ATH); 
  Kf = find(K)';
  if Kf,
	% Set irrelevant flag for non-tonal components.
	DFlags(Non_tonal_list(Kf, INDEX)) = IRRELEVANT; 
	% Delete rows in the non-tonal-list for the irrelevant non tonal
    % components.
	DNon_tonal_list(Kf, :) = []; 
  end 
end 
% --------------------

% -- Tonal case -- 
% Part I
% Preset decimated tonal list
DTonal_list = Tonal_list; 
if not(isempty(Tonal_list)) 
  % Map linear frequency index to non-linear to index absolute threshold in
  % table TH.
  K = Tonal_list(:, SPL) < TH(Map(Tonal_list(:, INDEX)), ATH); 
  Kf = find(K)';
  if Kf,
	% Set irrelevant flag for tonal components.
	DFlags(Tonal_list(Kf, INDEX)) = IRRELEVANT; 
	% Delete rows containing information about irrelevant tonal components.
	DTonal_list(Kf,:) = [];
  end 
  
end

% Part II 
% Eliminate tonal components that are less than one half of critical band
% width from a neighbouring component AND their SPL is lower 
% (pp. 113 Step 5b).   
if not(isempty(DTonal_list))
  i = 1;
  while (i < length(DTonal_list(:, 1))),
	k      = DTonal_list(i, INDEX);
	k_next = DTonal_list(i + 1, INDEX);
	
	if (TH(Map(k_next), BARK) - TH(Map(k), BARK) < 0.5)
	  % Shortening of DTonal_list. No increment of loop index in order to
      % test the next component of already reduced list.
	  if (DTonal_list(i, SPL) < DTonal_list(i + 1, SPL))
		DTonal_list = ...
			DTonal_list([1:i - 1, i + 1:length(DTonal_list(:, 1))], :);
		DFlags(k) = IRRELEVANT;
 	  else
		DTonal_list = ...
			DTonal_list([1:i, i + 2:length(DTonal_list(:, 1))], :);
		DFlags(k_next) = IRRELEVANT;
	  end
	  
	  % NEW code for index increment in order to implement sliding window.
	  % Increment loop index i only if tonal components are not within a range
      % of 0.5 BARK! 
	else
	  i = i + 1;
	end

	% OLD code
	% i = i + 1;
  
  end % End loop over DTonal_list

end