find_tonal_components.m

这是一个包含对MPEG视频各种变换处理的Matlab程序包

function [Flags, Tonal_list, Non_tonal_list] = ...
   Find_tonal_components(X, TH, Map, CB) % assume fs = 44100 fs
%[Flags, Tonal_list, Non_tonal_list] = Find_tonal_components(X, TH, Map, CB)
%
%   Identifie and list both tonal and non-tonal components of the audio
%   signal. It is assume in this implementation that the frequency
%   sampling fs is 44100 Hz. Details bare given in [1, pp. 112].
%
%   See also Decimation
   
%   Author: Fabien A. P. Petitcolas
%           Computer Laboratory
%           University of Cambridge
%
%   Copyright (c) 1998--2001 by Fabien A. P. Petitcolas
%   $Header: /Matlab MPEG/Find_tonal_components.m 5     9/12/02 11:23 Fabienpe $
%   $Id: Find_tonal_components.m,v 1.4 1998-07-07 14:39:54+01 fapp2 Exp $

%   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.
%-------------------------------------------------------------------------------
Common;

% Check input parameters
if (length(X) ~= FFT_SIZE)
   error('Unexpected power density spectrum size.');
end

if (DRAW),
   t = 1:length(X);
end

% List of flags for all the frequency lines (1 to FFT_SIZE / 2)
Flags = zeros(FFT_SIZE / 2, 1) + NOT_EXAMINED;

% Label the local maxima
local_max_list = [];
counter = 1;
for k = 2:FFT_SIZE / 2 -  1, % Don't care avout the borders
   if (X(k) > X(k-1) & X(k) >= X(k+1) & k > 2 & k <= 250)
      local_max_list(counter, INDEX) = k;
      local_max_list(counter, SPL) = X(k);
      counter = counter + 1;
   end
end
if (DRAW),
   disp('Local maxima.');
   plot(t, X(t), local_max_list(:, INDEX), local_max_list(:, SPL), 'ko');
   xlabel('Frequency index'); ylabel('dB'); title('Local maxima.');
   axis([0 256 0 100]); pause;
end

% List tonal components and compute sound pressure level
Tonal_list = [];
counter = 1;
if not(isempty(local_max_list))
	for i = 1:length(local_max_list(:, 1)),
	   k = local_max_list(i, INDEX);
	   is_tonal = 1;
	   
	   % Layer I
	   % Examine neighbouring frequencies
	   if (2 < k & k < 63)
	      J = [-2 2];
	   elseif (63 <= k & k < 127)
	      J = [-3 -2 2 3];
	   elseif (127 <= k & k < 250)
	      J = [-6:-2, 2:6];
	   else
	      is_tonal = 0;
	   end
	   
	   for j = J,
	      is_tonal = is_tonal & (X(k) - X(k + j) >= 7);
	   end
	   
	   % If X(k) is actually a tonal component then the following are listed
	   %    - index number k of the spectral line
	   %    - sound pressure level
	   %    - set tonal flag
	   if is_tonal
	      Tonal_list(counter, INDEX) = k;
	      Tonal_list(counter, SPL) = 10 * log10(10^(X(k - 1) / 10) + ...
	         10^(X(k) / 10) + 10^(X(k + 1) / 10));
	      Flags(k) = TONAL;
	      for j = [J -1 1],
	         Flags(k + j) = IRRELEVANT;
	      end
	      counter = counter + 1;
	   end
   end
	if (DRAW),
	   disp('Tonal components');
	   plot(t, X(t), Tonal_list(:, INDEX), Tonal_list(:, SPL), 'ro');
	   xlabel('Frequency index'); ylabel('dB'); title('Tonal components');
	   axis([0 256 0 100]); pause;
   end
end
% List the non tonal components and compute power
% All the spectral lines that have not been examined during the previous
% search are summed together to form the non-tonal component.
Non_tonal_list = [];
counter = 1;
for i = 1:length(CB(:, 1)) - 1,,
   % For each critical band, compute the power
   % in non-tonal components
   power  = MIN_POWER; % Partial sum
   weight = 0; % Used to compute the geometric mean of the critical band
   for k = TH(CB(i), INDEX):TH(CB(i + 1), INDEX) - 1, % In each critical band
      if (Flags(k) == NOT_EXAMINED),
         power    = 10 * log10(10^(power / 10) + 10^(X(k) / 10));
         weight   = weight + 10^(X(k) / 10) * (TH(Map(k), BARK) - TH(CB(i), BARK)');
         Flags(k) = IRRELEVANT;
      end
   end
   
   % The index number for the non tonal component is the index nearest
   % to the geometric mean of the critical band
   if (power <= MIN_POWER)
      index = round(mean(TH(CB(i), INDEX), TH(CB(i + 1), INDEX)));
   else
      index = TH(CB(i), INDEX) + round(weight / 10^(power / 10) * ...
         (TH(CB(i + 1), INDEX) - TH(CB(i), INDEX)));
   end
   if (index < 1)
      index = 1;
   end
   if (index > length(Flags))
      index = length(Flags);
   end
   if (Flags(index) == TONAL)
      index = index + 1; % Two tonal components cannot be consecutive
   end
   
   % For each subband
   %   - index of the non-tonal component
   %   - sound pressure level of this component
   Non_tonal_list(i, INDEX) = index;
   Non_tonal_list(i, SPL) = power;
   Flags(index) = NON_TONAL;
end

if (DRAW),
   disp('Tonal and non-tonal components');
   plot(t, X(t), Tonal_list(:, INDEX), Tonal_list(:, SPL), 'ro', ...
      Non_tonal_list(:, INDEX), Non_tonal_list(:, SPL), 'go');
   xlabel('Frequency index'); ylabel('dB'); 
   title('Tonal and non-tonal components'); 
   axis([0 256 0 100]); pause;
end