ltmin.m

音频的水印加入算法

function  LTmin = LTmin(LTg, NumberOfBands) 
%
%   Authors: Fabien A.P. Petitcolas ([e-mail])
%            Teddy Furon ([e-mail])
%
%   Changes:
%            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. 
%----------------------------------------------------------------------------
% LTmin = LTmin(LTg, NumberOfBands) 
% 
%   Find the minimum of the global masking threshold for each subband. 
%   [1, pp. 114] 
% 
% -- INPUT --
% LTq: Vector with (106 for fs = 44.1 kHz?) elements containing the loudness
% threshold values in dB.
%  
% NumberOfBands: Integer value. For Blocksize = 512 samples this value is
% one of the elements of the array [16, 32, 64, 128, 256].
%  
% -- OUTPUT --
% LTmin: Vector with FFT_SIZE/2 elements containing the minium loudness
% threshold values in dB.
% ------------
%
%   See also Global_masking_threshold
%--------------------------------------------------------------------------- 
 
global Map FFT_SIZE

% Calculate the size of each sub-band
SubbandWidth = (FFT_SIZE / 2) / NumberOfBands;
if SubbandWidth == 1
  LTmin = LTg( Map(1:FFT_SIZE/2)' );
else
  
  % Build indexing matrix for calculation of the minimum. B = reshape(A,m,n)
  % returns the m-by-n matrix B whose elements are taken column-wise from A. An
  % error results if A does not have m*n elements.
  ind = reshape(1:FFT_SIZE/2, SubbandWidth, NumberOfBands);

  % Map matrix ind to matrix containing as elements the 106 non-linear
  % distributed coefficients. Index LTg array with ind matrix to create matrix
  % containing the LTg values in the corresponding columns.
  table = LTg( Map(ind) );
  % Compute minimum of each column 
  LTmin = min(table); 
end