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freqz

Frequency response of filter

Syntax

[h,w] = freqz(sysobj)
[h,w] = freqz(sysobj,n)
[h,w] = freqz(sysobj,Name,Value)
freqz(sysobj)

Description

[h,w] = freqz(sysobj) returns the complex frequency response h of the filter System object™, sysobj. The vector w contains the frequencies (in radians) at which the function evaluates the frequency response. The frequency response is evaluated at 8192 points equally spaced around the upper half of the unit circle.

[h,w] = freqz(sysobj,n) returns the complex frequency response of the filter System object and the corresponding frequencies at n points equally spaced around the upper half of the unit circle.

freqz uses the transfer function associated with the filter to calculate the frequency response of the filter with the current coefficient values.

[h,w] = freqz(sysobj,Name,Value) returns a frequency response with additional options specified by one or more Name,Value pair arguments.

freqz(sysobj) uses fvtool to plot the magnitude and unwrapped phase of the frequency response of the filter System object sysobj.

For more information about optional input arguments for freqz, refer to freqz in Signal Processing Toolbox™ documentation.

Input Arguments

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sysobj

Filter System object.

The following Filter System objects are supported by this analysis function:

dsp.SampleRateConverter is also supported by freqz.

n

Number of samples. For an FIR filter where n is a power of two, the computation is done faster using FFTs.

Default: 8192

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside single quotes (' '). You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

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Specify the arithmetic used during analysis. When you specify 'double' or 'single', the function performs double- or single-precision analysis. When you specify 'fixed' , the arithmetic changes depending on the setting of the CoefficientDataType property and whether the System object is locked or unlocked.

 Details for Fixed-Point Arithmetic

When you do not specify the arithmetic for non-CIC structures, the function uses double-precision arithmetic if the filter System object is in an unlocked state. If the System object is locked, the function performs analysis based on the locked input data type. CIC structures only support fixed-point arithmetic.

Output Arguments

h

Complex n-element frequency response vector. If n is not specified, the function uses a default value of 8192.

w

Frequency vector of length n, in radians/sample. w consists of n points equally spaced around the upper half of the unit circle (from 0 to π radians/sample). If n is not specified, the function uses a default value of 8192.

Examples

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This examples plot the frequency response of the lowpass FIR filter using freqz.

b = fir1(80,0.5,kaiser(81,8));
firFilt = dsp.FIRFilter('Numerator',b);
freqz(firFilt);

Tips

There are several ways of analyzing the frequency response of filters. freqz accounts for quantization effects in the filter coefficients, but does not account for quantization effects in filtering arithmetic. To account for the quantization effects in filtering arithmetic, refer to function noisepsd.

Algorithms

freqz calculates the frequency response for a filter from the filter transfer function Hq(z). The complex-valued frequency response is calculated by evaluating Hq(ejω) at discrete values of w specified by the syntax you use. The integer input argument n determines the number of equally-spaced points around the upper half of the unit circle at which freqz evaluates the frequency response. The frequency ranges from 0 to π radians per sample when you do not supply a sampling frequency as an input argument. When you supply the scalar sampling frequency fs as an input argument to freqz, the frequency ranges from 0 to fs/2 Hz.

See Also

Functions

Introduced in R2011a

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