• Nie Znaleziono Wyników

Description Syntax freqz

N/A
N/A
Info
Pobierz
Protected

Academic year: 2021

Share "Description Syntax freqz"

Copied!
5
0
0

Ładowanie.... (Zobacz pełny tekst teraz)

Pobierz teraz ( 5 Stron )

Pełen tekst

(1)

Signal Processing Toolbox

freqz

Compute the frequency response of digital filters

Syntax

[h,w]= freqz(b,a,l) h = freqz(b,a,w)

[h,w] = freqz(b,a,l,' whole') [h,f] = freqz(b,a,l,fs)

h = freqz(b,a,f,fs)

[h,f] = freqz(b,a,l,' whole',fs) [h,f,s] = freqz(...)

freqz(b,a,...) freqz(Hd)

Description

[h,w] = freqz(b,a,l) returns the frequency response vector h and the corresponding angular frequency vector w for the digital filter whose transfer function is determined by the (real or complex) numerator and denominator polynomials represented in the vectors b and a, respectively. The vectors h and w are both of length l. The angular frequency vector w has values ranging from 0 to

radians per sample. When you don't specify the integer l, or you specify it as the empty vector [], the frequency response is calculated using the default value of 512 samples.

h = freqz(b,a,w) returns the frequency response vector h calculated at the frequencies (in radians per sample) supplied by the vector w. The vector w can have any length.

[h,w] = freqz(b,a,l,' whole') uses n sample points around the entire unit

circle to calculate the frequency response. The frequency vector w has length l

and has values ranging from 0 to 2 radians per sample.

(2)

[h,f] = freqz(b,a,l,fs) returns the frequency response vector h and the corresponding frequency vector f for the digital filter whose transfer function is determined by the (real or complex) numerator and denominator polynomials represented in the vectors b and a, respectively. The vectors h and f are both of length l. For this syntax, the frequency response is calculated using the sampling frequency specified by the scalar fs (in hertz). The frequency vector f is

calculated in units of hertz (Hz). The frequency vector f has values ranging from 0 to fs/2Hz.

h = freqz(b,a,f,fs) returns the frequency response vector h calculated at the frequencies (in Hz) supplied in the vector f. The vector f can be any length.

[h,f] = freqz(b,a,l,' whole',fs) uses n points around the entire unit circle to calculate the frequency response. The frequency vector f has length l and has values ranging from 0 to fsHz.

[h,f,s] = freqz(b,a,l,' whole',fs) returns the optional string argument s, specifying the units for the frequency vector f. The string returned in s is 'Hz', denoting hertz.

freqz(b,a,...) plots the magnitude and unwrapped phase of the frequency response of the filter. The plot is displayed in the current figure window.

freqz(Hd) plots the magnitude and unwrapped phase of the frequency response of the filter. The plot is displayed in fvtool . The input Hd is a dfilt filter object or an array of dfilt filter objects.

Remarks

It is best to choose a power of two for the third input argument n , because freqz uses an FFT algorithm to calculate the frequency response. See the reference description of fft for more information.

Examples

Plot the magnitude and phase response of an FIR filter:

(3)

b = fir1(80,0.5,kaiser(81,8));

freqz(b,1);

The same example using a dfilt object and displaying the result in the Filter

Visualization Tool ( fvtool) is

(4)

b = fir1(80,0.5,kaiser(81,8));

Hd = dfilt.df1(b);

freqz(Hd);

Algorithm

The frequency response [1] of a digital filter can be interpreted as the transfer

function evaluated at z = e

j

. You can always write a rational transfer function in

the following form.

(5)

freqz determines the transfer function from the (real or complex) numerator and denominator polynomials you specify, and returns the complex frequency response H(e

j

) of a digital filter. The frequency response is evaluated at sample points determined by the syntax that you use.

freqz generally uses an FFT algorithm to compute the frequency response whenever you don't supply a vector of frequencies as an input argument. It computes the frequency response as the ratio of the transformed numerator and denominator coefficients, padded with zeros to the desired length.

When you do supply a vector of frequencies as an input argument, then freqz evaluates the polynomials at each frequency point using Horner's method of nested polynomial evaluation [1], dividing the numerator response by the denominator response.

See Also

abs , angle , fft , filter , freqs , impz , invfreqs , logspace

References

[1] Oppenheim, A.V., and R.W. Schafer, Discrete-Time Signal Processing, Prentice-Hall, 1989, pp. 203-205.

freqspace fvtool

Cytaty

Pobierz teraz ( PDF - 5 Stron - 153.08 KB )

Powiązane dokumenty

A Note on the Torsion of a Vector Fie

The torsion of the null vector field on M relative to the affine connection T equals to the torsion tensor of the linear connection T whose extension by the canonical form is

Abstract. Let X be a real or complex vector space equipped with the strongest vector space topology τ

Here we shall offer simplified proofs of these results by showing that the topology τ max is also complete and coincides with τ max LC on countable-dimensional spaces.. The author

Extensions of weaker vector topologies from a subspace to the whole topological vector space

In [1] it was used in proving that every infinite-dimensional Fréchet space, non-isomorphic to со, admits a strictly weaker complete locally convex topology with the

a) Find the corresponding accumulation function a(t).

Ile wyniosły stopy procentowe w kolejnych kwartałach, jeśli wiadomo, że po roku pan Racisław odebrał 1200 zł, stopa procentowa w pierwszym kwartale była o połowę wyższa od

1. A vector equation of a line is , t  . Find the equation of this line in the form ax + by = c, where a, b, and c  .

A miniature car moves in a straight line, starting at the point (2, 0).. Eventually, the two miniature

1. The following is a cumulative frequency diagram for the time t, in minutes, taken by 80 students to complete a task. (a) Write down the median.

The following is a cumulative frequency diagram for the time t, in minutes, taken by 80 students to complete a task.. (a) Write down

Description Syntax filter

The filter function filters a data sequence using a digital filter which works for both real and complex inputs.. The filter is a direct form

Description Syntax freqz

The optional output argument href is the frequency response of the transfer function associated with the reference filter used to specify the quantized filter hq.. [h,f]