syredi

Design of iir filters, syredi code interface

Calling Sequence

[fact,b2,b1,b0,c1,c0,zzeros,zpoles]=syredi(ityp,iapro,om,deltap,deltas)

Arguments

itype integer, the filter type:  1 stands for low-pass, 2 for high- pass, 3 for band-pass, 4 for stop-band.

: :iappro integer, the design approximation type: 1 stands for

butterworth, 2 for elliptic, 3 for Chebytchev1, 4 for Chebytchev2.

: :om 4-vector of cutoff frequencies (in radians)

om=[om1,om2,om3,om4], `` 0<= om1 <= om2 <= om3 <= om4 <= pi . When ftype`=’lp’ or `’hp’, om3 and om4 are not used and may be set to 0.

: :deltap a real scalar, the ripple in the passband. 0< deltap <1 : :deltas a real scalar, the ripple in the stopband. 0< deltas <1 : :gain scalar, the filter gain : :b2 real row vector, degree 2 coefficients of numerators. : :b1 real row vector, degree 1 coefficients of numerators. : :b0 real row vector, degree 0 coefficients of numerators. : :c1 real row vector, degree 1 coefficients of denominators. : :c0 real row vector, degree 0 coefficients of denominators. : :zzeros complex row vector, filter zeros in the z-domain : :zpoles complex row vector, filter poles in the z-domain :

Description

Computes iir filter approximation. The result is given as a set of second order transfer functions Hi=(b0(i)+b1(i)*z+b2(i)*z^2)/(c0(i)+c1(i)*z+z^2) and also as a poles, zeros, gain representation.

The filter obtained is h=fact*H1*...*Hn.

Remark

This built-in function is mainly intended to be used by the eqiir function.

References

The syredi code is derived from doredi package written by Guenter F. Dehner, Institut fuer Nachrichtentechnik Universitaet Erlangen- Nuernberg, Germany.

Dehner,G.F. 1979, DOREDI: Program for Design and Optimization of REcursive DIgital filters-Programs for Digital Signal Processing, ed:Digital Signal Processing committee of IEEE Acoustics, Speech and Signal Processing Society.

For DOREDI.f source code see http://michaelgellis.tripod.com/dsp/pgm25.html

Examples

[fact,b2,b1,b0,c1,c0,zzeros,zpoles]=syredi(1,4,[2*%pi/10,4*%pi/10,0,0],0.02,0.001);
h=fact*(b0+b1*%z+b2*%z^2)./(c0+c1*%z+%z^2)

See Also

• eqiir Design of iir filters