global_masking_threshold.m

音频的水印加入算法

function  LTg = Global_masking_threshold(LTt, LTn) 
%
%   Authors: Fabien A.P. Petitcolas ([e-mail])
%            Computer Laboratory 
%            University of Cambridge 
%
%            Teddy Furon ([e-mail])
%            Laboratoire TSI - Telecom Paris
%            UIIS Lab - Thomson multimedia R&D France 
%
%   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. 
%---------------------------------------------------------------------------- 
%
%   LTg = Global_masking_threshold(LTt, LTn) 
% 
%   Compute the global masking threshold for the subset of frequency lines  
%   defined in table [1, pp. 117]. It is the sum -- in the normal square 
%   amplitude scale of the spectrum -- of the individual masking 
%   thresholds and the absolute threshold [1, pp. 114]. 
% 
% -- INPUT --
% LTt: Matrix of size (length Tonal_list)x(length(TH(:, 1) = 106 for fs =
% 44.1 kHz)
% LTn: Matrix of size (length Non_tonal_list)x(length(TH(:, 1) = 106 for fs =
% 44.1 kHz)
%  
% -- OUTPUT --
% LTq: Vector with (106 for fs = 44.1 kHz) elements containing the loudness
% threshold values in dB.
% ------------
%  
%   See also Individual_masking_thresholds
%----------------------------------------------------------------------------- 

global LTq MIN_POWER
  
% Sum the powers of the threshold in quiet and the individual masking
% threshold of the non-tonal maskers. For vectors, sum(X) is the sum of the
% elements of X. For matrices, sum(X) is a row vector with the sum over each
% column.
temp = 0.0;
idx = [];
colsum = [];

colsum = sum(10.0 .^ (LTn ./ 10.0));
temp = 10.0 .^ (LTq' ./ 10.0) + colsum; 

% Contribution of the tonal component if not empty. 
if not(isempty(LTt))  
  temp = temp + sum(10 .^ (LTt ./ 10), 1); 
end    

% Calculate global masking threshold in dB.
LTg = 10.0 * log(temp)./log(10.0);