Logarithmischer Frequenz- und Phasengang eines Filters.

» b=fir1( 32, 0.25, boxcar(33) );
» freqz (b);

Dieser Aufruf gibt obige Darstellung von Frequenz- und Phasengang des Filters aus.

Bei folgender Befehlsfolge:

» b=fir1( 32, 0.25, boxcar(33) );
» f=freqz (b);

wird dem Vektor f der Frequenzgang in Real- und Imaginärteil zugewiesen.
Es wird keine grafische Darstellung ausgegeben.

So kann nun z.B. der Frequenzganz in linearem Maßstab dargestellt werden, mit

» b=fir1( 32, 0.25, boxcar(33) );
» f=freqz (b);
» plot ( abs(f) );

» help freqz

FREQZ Z-transform digital filter frequency response.
When N is an integer, [H,W] = FREQZ(B,A,N) returns the N-point frequency
vector W in radians and the N-point complex frequency response vector H
of the filter B/A:
                          -1                -nb 
   jw  B(z)   b(1) + b(2)z + .... + b(nb+1)z
H(e) = ---- = ----------------------------
                          -1                -na
       A(z)     1  + a(2)z + .... + a(na+1)z

given numerator and denominator coefficients in vectors B and A. The
frequency response is evaluated at N points equally spaced around the
upper half of the unit circle. If N isn't specified, it defaults to 512.

[H,W] = FREQZ(B,A,N,'whole') uses N points around the whole unit circle.

H = FREQZ(B,A,W) returns the frequency response at frequencies 
designated in vector W, in radians (normally between 0 and pi).

[H,F] = FREQZ(B,A,N,Fs) and [H,F] = FREQZ(B,A,N,'whole',Fs) given a 
sampling freq Fs in Hz return a frequency vector F in Hz.

H = FREQZ(B,A,F,Fs) given sampling frequency Fs in Hz returns the 
complex frequency response at the frequencies designated in vector F,
also in Hz.

FREQZ(B,A,...) with no output arguments plots the magnitude and
unwrapped phase of B/A in the current figure window.

See also FILTER, FFT, INVFREQZ, FREQS and GRPDELAY.