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Hi all,
I have builded a function of impulse response in matlab from pole and zero functions I adopted from the internet but I'm not so sure about the result....anyone can help me please ? perhaps I made mistakes on the function The impulse response, h(n), of the weighted synthesis filter H(z)W(z) =A(z/g1)/[A'(z)A(z/g2)] is computed each subframe. This impulse response is needed for the search of adaptive and fixed codebooks. The impulse response h(n), is computed by filtering the vector of coefficients of the filter A(z/g1) extended by zeros through the two filters 1/A'(z) and 1/A(z/g2). function h=impulse_res(fc,pc,no,cmp) %cmp = codec mode in AMR system for choosing gamma values (for example : 12.2 kbps ) %no (the order of LPC) %fc = the set vector of quantized LP coefficient A'(z) (size = 11x1) %pc = the set vector of unquantized LP coefficient A(z)(size = 11x1) %h = impulse response (size 40x1) L@; %L=size of each subframe(40 samples) h=zeros(L,1);h(1)=1.0; d1=zeros(no+1,1); d2=zeros(no+1,1); d3=zeros(no+1,1); %for A(z/y1) if (cmp=.2) gamma1=0.9; else gamma1=0.94; end pcexp2=bwex(gamma1,pc,no); [d1,h]=zero(pcexp2,no,d1,h,L); %for 1/A(z) [d2,h]=pole(fc,no,d2,h,L); %for 1/A(z/y2) gamma2=0.6; pcexp1=bwex(gamma2,pc,no); [d3,h]=pole(pcexp1,no,d3,h,L); ---------------------- function pcexp = bwex( gamma, pc, no ) % SCALE PREDICTOR COEFFICIENTS TO SHIFT POLES RADIALLY INWARD pcexp( 1:no+1, 1 ) = ( pc( 1:no+1 ) .* ( gamma .^ (0:no)' ) ); ----- function [ d, h ] = pole(pcexp, no, d, h, L ) if pcexp(1) ~= 1.0 fprintf( 'polefilt: bad coefficients\no'); end for t = 1:L d(1) = h(t) - sum( d(2:n+1) .* pcexp(2:n+1) ); d(2:n+1) = d(1:n); h(t) = d(1); end ------- function [ d, h ] = zero( pcexp, no, d, h, L ) for t = 1:len d(1) = h(t); ar = sum( d(2:n+1) .* pcexp(2:n+1) ); d(2:n+1) = d(1:n); h(t) = ar + ( d(1) * pcexp(1) ); end ------------------------------- * Example the inputs are : fc = [1, -2.6668, 4.8836, -6.2675, 5.2687, -2.2201, -1.6791, 4.6678, -4.8297, 3.1372, -1.2942]; pc = [1, -9.113, 38.056, -95.897, 161.47, -189.84, 157.81, - 91.597, 35.525, -8.314, 0.89166]; no = 10 ; cmp = 7.95; the output is : h =[ 1.0000 -0.4316 -3.0501 0.0726 6.2639 1.4851 -9.2364 -5.1018 9.4839 7.0807 -9.9621 -13.4065 -1.1086 5.2565 1.4810 -6.9308 -17.2031 -11.5825 15.7709 19.8724 -19.9871 -36.0993 9.3675 35.4143 -7.4783 -40.0359 -14.3673 8.2341 4.4951 5.3959 -14.8422 -50.8667 -7.5202 73.2907 18.7850 -99.2104 -43.5024 89.4611 34.5656 -87.3220]; |
Building an impulse response function in MATLAB
Started by ●July 31, 2003
