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freqz

Frequency response of discrete-time filterSystem object

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Syntax

[h,w] = freqz(sysobj)
[h,w] = freqz(sysobj,n)
[h,w] = freqz(sysobj,'Arithmetic',arithType)
freqz(sysobj)

Description

[h,w] = freqz(sysobj)returns the complex frequency responsehof the filter System object™,sysobj. The vectorwcontains the frequencies (in radians/sample) 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 atnpoints equally spaced around the upper half of the unit circle.

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

[h,w] = freqz(sysobj,'Arithmetic',arithType)analyzes the filter System object, based on the arithmetic specified inarithType, using either of the previous syntaxes.

example

freqz(sysobj)usesfvtoolto plot the magnitude and unwrapped phase of the frequency response of the filter System objectsysobj.

For more input options, seefreqzin Signal Processing Toolbox™.

Examples

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Open Live Script

这个例子情节的频率响应owpass FIR filter usingfreqz.

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

Figure Filter Visualization Tool - Magnitude Response (dB) and Phase Response contains an axes and other objects of type uitoolbar, uimenu. The axes with title Magnitude Response (dB) and Phase Response contains an object of type line.

Input Arguments

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Number of points over which the frequency response is computed. For an FIR filter wherenis a power of two, the computation is done faster using FFTs.

Data Types:single|double|int8|int16|int32|int64|uint8|uint16|uint32|uint64

Arithmetic used in the filter analysis, specified as'double','single', or'Fixed'. When the arithmetic input is not specified and the filter System object is unlocked, the analysis tool assumes a double-precision filter. When the arithmetic input is not specified and the System object is locked, the function performs the analysis based on the data type of the locked input.

The'Fixed'value applies to filter System objects with fixed-point properties only.

When the'Arithmetic'input argument is specified as'Fixed'and the filter object has the data type of the coefficients set to'Same word length as input', the arithmetic analysis depends on whether the System object is unlocked or locked.

  • unlocked –– The analysis object function cannot determine the coefficients data type. The function assumes that the coefficients data type is signed, has a 16-bit word length, and is auto scaled. The function performs fixed-point analysis based on this assumption.

  • locked –– When the input data type is'double'or'single', the analysis object function cannot determine the coefficients data type. The function assumes that the data type of the coefficients is signed, has a 16-bit word length, and is auto scaled. The function performs fixed-point analysis based on this assumption.

To check if the System object is locked or unlocked, use theisLockedfunction.

When the arithmetic input is specified as'Fixed'and the filter object has the data type of the coefficients set to a custom numeric type, the object function performs fixed-point analysis based on the custom numeric data type.

Output Arguments

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Complexn-element frequency response vector. Ifnis not specified, the function uses a default value of 8192. The frequency response is evaluated atnpoints equally spaced around the upper half of the unit circle.

Data Types:double
Complex Number Support:Yes

Frequency vector of lengthn, in radians/sample.wconsists ofnpoints equally spaced around the upper half of the unit circle (from 0 toπradians/sample). Ifnis not specified, the function uses a default value of 8192.

Data Types:double

Tips

There are several ways of analyzing the frequency response of filters.freqzaccounts 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 functionnoisepsd.

Algorithms

freqzcalculates the frequency response for a filter from the filter transfer functionHq(z). The complex-valued frequency response is calculated by evaluatingHq(ejω) at discrete values ofw你使用指定的语法。整数输入argumentndetermines the number of equally-spaced points around the upper half of the unit circle at whichfreqzevaluates 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 frequencyfsas an input argument tofreqz, the frequency ranges from 0 tofs/2 Hz.

See Also

Functions

Topics

Introduced in R2011a

DSP System Toolbox Documentation

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