zpkftransf (Filter Design Toolbox)

Zero-pole-gain frequency transformation of the digital filter

Syntax

[Z2,P2,K2] = zpkftransf(Z,P,K,AllpassNum,AllpassDen)

Description

[Z2,P2,K2] = zpkftransf(Z,P,K,AllpassNum,AllpassDen) returns zeros, Z₂, poles, P₂, and gain factor, K₂, of the transformed lowpass digital filter. The prototype lowpass filter is given with zeros, Z, poles, P, and gain factor, K. If AllpassDen is not specified it will default to 1. If neither AllpassNum nor AllpassDen is specified, then the function returns the input filter.

Examples

Design a prototype real IIR halfband filter using a standard elliptic approach:

[b, a] = ellip(3,0.1,30,0.409);
[AlpNum, AlpDen] = allpasslp2lp(0.5, 0.25);
[z2, p2, k2] = zpkftransf(roots(b),roots(a),b(1),AlpNum,AlpDen);

Verify the result by comparing the prototype filter with the target filter:

```
fvtool(b, a, k2*poly(z2), poly(p2));
```

Arguments
Z
Zeros of the prototype lowpass filter

P
Poles of the prototype lowpass filter

K
Gain factor of the prototype lowpass filter

FTFNum
Numerator of the mapping filter

FTFDen
Denominator of the mapping filter

Z2
Zeros of the target filter

P2
Poles of the target filter

K2
Gain factor of the target filter

See Also
iirftransf

zpkbpc2bpc zpklp2bp