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Lattice Filter Structures 247
function [K,C] = dir2ladr(b,a)
% IIR Direct form to pole-zero Lattice/Ladder form Conversion
% -----------------------------------------------------------
% [K,C] = dir2ladr(b,a)
% K = Lattice coefficients (reflection coefficients), [K1,...,KN]
% C = Ladder Coefficients, [C0,...,CN]
% b = Numerator polynomial coefficients (deg N
error(’ *** length of b must be N, the numerator A N (z)
should be divided into the denominator B M (z) using the deconv function
to obtain a proper rational part and a polynomial part. The proper
rational part can be implemented using a lattice-ladder structure, while
the polynomial part is implemented using a direct structure.
To convert a lattice-ladder form into a direct form, we first use the
recursive procedure in (6.21) on {K m } coefficients to determine {a N (k)}
and then solve (6.27) recursively to obtain {b M (k)}. This is done in the
following MATLAB function ladr2dir.
function [b,a] = ladr2dir(K,C)
% Lattice/Ladder form to IIR Direct form Conversion
% -------------------------------------------------
% [b,a] = ladr2dir(K,C)
% b = numerator polynomial coefficients
% a = denominator polymonial coefficients
% K = Lattice coefficients (reflection coefficients)
% C = Ladder coefficients
%
N = length(K); M = length(C);
C = [C, zeros(1,N-M+1)];
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