tt.m

ADPCM的MATLAB的实现

p = wavread('ringin.WAV');
indexTable = [-1, -1, -1, -1, 2, 4, 6, 8, -1, -1, -1, -1, 2, 4, 6, 8];
stepsizeTable = [ 7, 8, 9, 10, 11, 12, 13, 14, 16, 17,19, 21, 23, 25, 28, 31, 34, 37, 41, 45,50, 55, 60, 66, 73, 80, 88, 97, 107, 118,130, 143, 157, 173, 190, 209, 230, 253, 279, 307,337, 371, 408, 449, 494, 544, 598, 658, 724, 796,876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066,2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358,5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767];
valpred = 0;
i=1;
index=1;
p=32767*p;
while i <= length(p)
    step = stepsizeTable(index);
    diff = p(i)-valpred;
    if (diff < 0)
        sign = 8;
    else sign = 0;
    end
     if (sign==8)
         diff = (-diff);
     end
     vpdiff = step/8;
     
     % Step 2 - Divide and clamp */
	 % Note:
	 % This code *approximately* computes:
     %  delta(i-44) = diff*4/step;
	 %   vpdiff = (delta(i-44)+0.5)*step/4;
	 % but in shift step bits are dropped. The net result of this is
	 % that even if you have fast mul/div hardware you cannot put it to
	 % good use since the fixup would be too expensive.
	 %
     delta(i) = 0;
     if ( diff >= step ) 
	    delta(i) = 4;
	    diff = diff-step;
	    vpdiff = vpdiff+step;
    end
    
    step = step/2;
    if ( diff >= step  ) 
	    delta(i)=bitor(delta(i),2);
	    diff=diff-step;
	    vpdiff =vpdiff+step;
    end
    
    step=step/2;
	if ( diff >= step )
	  delta(i)=bitor(delta(i),1);
	    vpdiff=vpdiff+step;
    end
   % Step 3 - Update previous value 
	 if (sign==8)
         valpred=valpred-vpdiff;
     else
         valpred=valpred+vpdiff;
     end
% Step 4 - Clamp previous value to 16 bits 
   if ( valpred > 32767 )
	  valpred = 32767;
	else if ( valpred < -32768 )
	  valpred = -32768;
  end
end
% Step 5 - Assemble value, update index and step values 
  delta(i)=bitor(delta(i),sign);
  index=index+indexTable(delta(i)+1);
	if ( index < 1 ) index =1;
    else if ( index > 89 ) index = 89;
        end
    end
	step = stepsizeTable(index);   
   i=i+1;
end



j=1;
index=1;
valpred=0;
while j<=length(delta)

% Step 2 - Find new index value (for later) */
	index=index+indexTable(delta(j)+1);
	if ( index < 1 ) index = 1;
    end
	if ( index > 89 ) index = 89;
    end
% Step 3 - Separate sign and magnitude */
	sign = bitand(delta(j),8);
	delta(j) = bitand(delta(j),7);

% Step 4 - Compute difference and new predicted value */
% Computes 'vpdiff = (delta+0.5)*step/4', but see comment
	% adpcm_coder.
%
	vpdiff = step /8;
	if ( bitand(delta(j),4)) vpdiff =vpdiff+step;
    end
	if (bitand(delta(j),2)) vpdiff=vpdiff+step/2;
    end
	if (bitand(delta(j),1)) vpdiff=vpdiff+step/4;
    end

	if ( sign==8 )
	  valpred=valpred-vpdiff;
	else
	  valpred=valpred+vpdiff;
  end
% Step 5 - clamp output value */
	if ( valpred > 32767 )
	  valpred = 32767;
	else if ( valpred < -32768 )
	  valpred = -32768;
      end
     end
%Step 6 - Update step value */
	step = stepsizeTable(index);
    j = j+1;
    t(j)=valpred;
end
t=t/32767;
wavwrite(t,16000,'ringincopy.wav');