ismaxphase(h) determines if the filter object h is maximum phase, and returns 1 if true and 0 if false. adapfilt, dfilt, and mfilt objects work with ismaxphase.

ismaxphase(h,tolerance) uses input argument tolerance to determine whether the zeros of the filter transfer function have values that are close enough to 1 to be considered 1 or greater (on or outside the unit circle, returning 1 if true (the difference between the coefficient value and 1 is less than tolerance) and 0 if not.

The phase determination is based on the reference coefficients. A filter is maximum phase when the zeros of its transfer function are on or outside the unit circle, or when the numerator is a scalar.

Examples

Two examples show ismaxphase in use. The first is a discrete-time dfilt object and the second an adaptive filter.

fp = 100;
fst= 120;
fs = 800;
ap = 1;
ast= 80;
d = fdesign.lowpass('fp,fst,ap,ast',fp,fst,ap,ast,fs);
h = design(d,'equiripple','minphase',true);
isminphase(h)

ans =

     1

To make this a maximum phase filter, use fliplr to change the coefficient order. Reordering the coefficients this way changes the phase from minimum to maximum.

h.numerator=fliplr(h.numerator);
ismaxphase(h)

ans =

     1

returns 1 so this is a maximum phase filter. Compare to isminphase.

For the adaptive filter example, try the following code:

x  = randn(1,500);     % Input to the filter
b  = fir1(31,0.5);     % FIR system to be identified
n  = 0.1*randn(1,500); % Observation noise signal
d  = filter(b,1,x)+n;  % Desired signal
mu = 1;                % NLMS step size
offset = 50;           % NLMS offset
ha = adaptfilt.nlms(32,mu,1,offset);
[y,e] = filter(ha,x,d);

After adapting, ha is an FIR filter that does not exhibit maximum phase.

ismaxphase(ha)

ans =

     0

ismaxphase - Determine whether filter is maximum phase

Syntax

Description

Examples

See Also