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dsp.FIRFilter

Static or time-varying FIR filter
静态或时变 FIR 滤波器

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Description 描述

The dsp.FIRFilter System object™ filters each channel of the input using static or time-varying FIR filter implementations.
dsp.FIRFilter System 对象™使用静态或时变 FIR 滤波器实现对输入的每个通道进行滤波。

To filter each channel of the input:
要滤波输入的每个通道：

  1. Create the dsp.FIRFilter object and set its properties.
    创建 dsp.FIRFilter 对象并设置其属性。

  2. Call the object with arguments, as if it were a function.
    使用参数调用对象，就好像它是一个函数一样。

To learn more about how System objects work, see What Are System Objects?
若要了解有关系统对象如何工作的详细信息，请参阅什么是系统对象？

This object supports C/C++ code generation and SIMD code generation under certain conditions. For more information, see Code Generation.
此对象在特定条件下支持 C/C++ 代码生成和 SIMD 代码生成。有关详细信息，请参阅代码生成。

Creation 创造

Syntax 语法

fir = dsp.FIRFilter
fir = dsp.FIRFilter(num)
fir = dsp.FIRFilter(Name,Value)

Description 描述

fir = dsp.FIRFilter returns a finite impulse response (FIR) filter object, fir, which independently filters each channel of the input over time using a specified FIR filter implementation.
fir = dsp.FIRFilter 返回一个有限脉冲响应 （FIR） 滤波器对象， fir 该对象使用指定的 FIR 滤波器实现随时间推移独立滤波输入的每个通道。

example 例

fir = dsp.FIRFilter(num) returns an FIR filter System object, fir, with the Numerator property set to num.
fir = dsp.FIRFilter(num) 返回一个 FIR 筛选器 System 对象 ， fir 并将 Numerator 属性设置为 num 。

fir = dsp.FIRFilter(Name,Value) returns an FIR filter System object, fir, with each property set to the specified value.
fir = dsp.FIRFilter(Name,Value) 返回一个 FIR 筛选器 System 对象 ， fir 其中每个属性都设置为指定值。

Properties 性能

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Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.
除非另有说明，否则属性是不可调的，这意味着在调用对象后无法更改其值。当您调用对象时，对象会锁定，并且 release 该函数会解锁它们。

If a property is tunable, you can change its value at any time.
如果属性是可调的，则可以随时更改其值。

For more information on changing property values, see System Design in MATLAB Using System Objects.
有关更改属性值的更多信息，请参阅使用系统对象在 MATLAB 中进行系统设计。

Specify the filter structure. You can specify the filter structure as one of Direct form | Direct form symmetric | Direct form antisymmetric | Direct form transposed | Lattice MA.

Specify the source of the filter coefficients as Property or Input port. When you specify Input port, the filter object updates the time-varying filter once every frame.

Dependencies

This applies when you set the Structure to Direct form | Direct form symmetric | Direct form antisymmetric | Direct form transposed.

Specify the source of the Lattice filter coefficients as Property or Input port. When you specify Input port, the filter object updates the time-varying filter once every frame.

Dependencies

This applies when you set the Structure to Lattice MA.

Specify the filter coefficients as a real or complex numeric row vector.

Tunable: Yes

Dependencies

This property applies when you set the NumeratorSource property to Property, and the Structure property is set to Direct form, Direct form symmetric, Direct form antisymmetric, or Direct form transposed.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64
Complex Number Support: Yes

Specify the reflection coefficients of a lattice filter as a real or complex numeric row vector.

Tunable: Yes

Dependencies

This property applies when you set the Structure property to Lattice MA, and the ReflectionCoefficientsSource property to Property.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64
Complex Number Support: Yes

Specify the initial conditions of the filter states. The number of states or delay elements equals the number of reflection coefficients for the lattice structure, or the number of filter coefficients–1 for the other direct form structures.

You can specify the initial conditions as a scalar, vector, or matrix. If you specify a scalar value, the FIR filter object initializes all delay elements in the filter to that value. If you specify a vector whose length equals the number of delay elements in the filter, each vector element specifies a unique initial condition for the corresponding delay element. The object applies the same vector of initial conditions to each channel of the input signal.

If you specify a vector whose length equals the product of the number of input channels and the number of delay elements in the filter, each element specifies a unique initial condition for the corresponding delay element in the corresponding channel.

If you specify a matrix with the same number of rows as the number of delay elements in the filter, and one column for each channel of the input signal, each element specifies a unique initial condition for the corresponding delay element in the corresponding channel.

Tunable: Yes

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

Fixed-Point Properties 定点属性

Specify whether to use full precision rules. If you set FullPrecisionOverride to true, which is the default, the object computes all internal arithmetic and output data types using full precision rules. These rules provide the most accurate fixed-point numerics. It also turns off the display of other fixed-point properties because they do not apply individually. These rules guarantee that no quantization occurs within the object. Bits are added, as needed, to ensure that no roundoff or overflow occurs. If you set FullPrecisionOverride to false, fixed-point data types are controlled through individual fixed-point property settings. For more information, see Full Precision for Fixed-Point System Objects.

Specify the rounding method.

Dependencies

This property applies only if the object is not in full precision mode.

Specify the overflow action as Wrap or Saturate.

Dependencies

This property applies only if the object is not in full precision mode.

Specify the coefficients fixed-point data type as Same word length as input or Custom.

Dependencies

This property applies when you set the NumeratorSource property to Property.

Specify the coefficients fixed-point type as a signed or unsigned numerictype (Fixed-Point Designer) object.

Dependencies

This property applies when you set the CoefficientsDataType property to Custom.

Specify the reflection coefficients fixed-point data type as Same word length as input or Custom.

Dependencies

This property applies when you set the ReflectionCoefficientsSource property to Property.

Specify the reflection coefficients fixed-point type as a signed or unsigned numerictype (Fixed-Point Designer) object.

Dependencies

This property applies when you set the ReflectionCoefficientsDataType property to Custom.

Specify the product fixed-point data type as Full precision, Same as input, or Custom.

Specify the product fixed-point type as a signed or unsigned scaled numerictype (Fixed-Point Designer) object.

Dependencies

This property applies when you set the ProductDataType property to Custom.

Specify the accumulator fixed-point data type to Full precision, Same as input, Same as product, or Custom.

Specify the accumulator fixed-point type as a signed or unsigned scaled numerictype (Fixed-Point Designer) object.

Dependencies

This property applies when you set the AccumulatorDataType property to Custom.

Specify the state fixed-point data type as one of Same as input, Same as accumulator, or Custom.

Dependencies

This property does not apply to any of the direct form or direct form I filter structures.

Specify the state fixed-point type as a signed or unsigned scaled numerictype (Fixed-Point Designer) object.

Dependencies

This property applies when you set the StateDataType property to Custom.

Specify the output fixed-point data type as one of Same as input, Same as accumulator, or Custom.

Specify the output fixed-point type as a signed or unsigned scaled numerictype (Fixed-Point Designer) object.

Dependencies

This property applies when you set the OutputDataType property to Custom.

Usage 用法

Syntax 语法

y = fir(x)
y = fir(x,coeff)

Description 描述

example 例

y = fir(x) applies an FIR filter to the real or complex input signal x to produce the output y.
y = fir(x) 将 FIR 滤波器应用于实数或复数输入信号 x 以产生输出 y 。

example 例

y = fir(x,coeff) uses the time-varying coefficients, coeff , to filter the input signal x and produce the output y. You can use this option when you set the NumeratorSource or ReflectionCoefficientsSource property to Input port.
y = fir(x,coeff) 使用时变系数 coeff ， 来滤除输入信号 x 并产生输出 y 。在将 NumeratorSource or 属性设置为 Input port 时 ReflectionCoefficientsSource ，可以使用此选项。

Input Arguments 输入参数

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Data input, specified as a vector or a matrix. When the input data is of a fixed-point type, it must be signed when the structure is set to Direct form symmetric or Direct form antisymmetric. The FIR filter object operates on each channel of the input signal independently over successive calls to the object.

This System object supports variable-size input.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | fi
Complex Number Support: Yes

Time-varying filter coefficients, specified as a row vector. The data and coefficient inputs must have the same data type.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | fi
Complex Number Support: Yes

Output Arguments 输出参数

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Filtered output, returned as a vector or a matrix. The output has the same size and data type as the input.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | fi
Complex Number Support: Yes

Object Functions 对象函数

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:
若要使用对象函数，请将 System 对象指定为第一个输入参数。例如，若要释放名为 obj 的 System 对象的系统资源，请使用以下语法：

release(obj)

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freqzFrequency response of discrete-time filter System object
fvtoolVisualize frequency response of DSP filters
impzImpulse response of discrete-time filter System object
infoInformation about filter System object
coeffsReturns the filter System object coefficients in a structure
costEstimate cost of implementing filter System object
grpdelayGroup delay response of discrete-time filter System object
generatehdlGenerate HDL code for quantized DSP filter (requires Filter Design HDL Coder)
outputDelayDetermine output delay of single-rate or multirate filter
stepRun System object algorithm
releaseRelease resources and allow changes to System object property values and input characteristics
resetReset internal states of System object

Examples 例子

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Use an FIR filter to apply a lowpass filter to a waveform with two sinusoidal components.
使用 FIR 滤波器将低通滤波器应用于具有两个正弦分量的波形。

  • Copy openExample Command
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  • Try This Example
 t = (0:1000)'/8e3;
 xin = sin(2*pi*0.3e3*t)+sin(2*pi*3e3*t);
 
 sr = dsp.SignalSource;
 sr.Signal = xin;
 sink = dsp.SignalSink;

 fir = dsp.FIRFilter(designLowpassFIR(FilterOrder=10,CutoffFrequency=0.5));

sa = spectrumAnalyzer(...
    'SampleRate',8e3,...
    'Method','welch',...
    'PlotAsTwoSidedSpectrum',false,...
    'OverlapPercent',80,...
    'SpectrumUnits','dBW',...
    'YLimits',[-150 -10]);

 while ~isDone(sr)
      input = sr();
      filteredOutput = fir(input);
      sink(filteredOutput);
      sa(filteredOutput)
 end

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  • Try This Example
 filteredResult = sink.Buffer;
 fvtool(fir,'Fs',8000)

Figure Figure 1: Magnitude Response (dB) contains an axes object. The axes object with title Magnitude Response (dB), xlabel Frequency (kHz), ylabel Magnitude (dB) contains an object of type line.

Design an FIR filter as a System object.
将 FIR 滤波器设计为 System 对象。

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N = 10;  
Fc = 0.4;
firFiltObj = designLowpassFIR(FilterOrder=N,CutoffFrequency=Fc,SystemObject=true)
firFiltObj = 
  dsp.FIRFilter with properties:

            Structure: 'Direct form'
      NumeratorSource: 'Property'
            Numerator: [-1.2414e-18 -0.0126 -0.0247 0.0635 0.2748 0.3981 0.2748 0.0635 -0.0247 -0.0126 -1.2414e-18]
    InitialConditions: 0

  Use get to show all properties

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fvtool(firFiltObj)

Figure Figure 2: Magnitude Response (dB) contains an axes object. The axes object with title Magnitude Response (dB), xlabel Normalized Frequency ( times pi blank rad/sample), ylabel Magnitude (dB) contains an object of type line.

Create a dsp.FIRFilter object, and set the NumeratorSource property to 'Input port' so that you can vary the coefficients of the FIR filter through the input port during simulation.
创建一个 dsp.FIRFilter 对象，并将 NumeratorSource 该属性设置为， 'Input port' 以便在仿真期间通过输入端口改变 FIR 滤波器的系数。

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firFilt = dsp.FIRFilter(NumeratorSource="Input port")
firFilt = 
  dsp.FIRFilter with properties:

            Structure: 'Direct form'
      NumeratorSource: 'Input port'
    InitialConditions: 0

  Use get to show all properties

Create a spectrumAnalyzer object to visualize the spectra of the input and output signals.
创建一个 spectrumAnalyzer 对象来可视化输入和输出信号的频谱。

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spectrumScope = spectrumAnalyzer(SampleRate=44100,PlotAsTwoSidedSpectrum=false,...
    ChannelNames=["Input Signal","Filtered Signal"]);

Create a dsp.DynamicFilterVisualizer object to visualize the magnitude response of the varying filter.
创建一个 dsp.DynamicFilterVisualizer 对象以可视化变化滤波器的幅度响应。

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filterViz = dsp.DynamicFilterVisualizer(NormalizedFrequency=true);

Stream in random data and filter the signal using the dsp.FIRFilter object. Use the designLowpassFIR function to design the filter coefficients. By default, this function returns a vector of FIR filter coefficients. Assign these coefficients to the dsp.FIRFilter object.
流式传输随机数据并使用 dsp.FIRFilter 对象过滤信号。使用该 designLowpassFIR 函数设计滤波器系数。默认情况下，此函数返回 FIR 滤波器系数的向量。将这些系数分配给 dsp.FIRFilter 对象。

Vary the cutoff frequency of the filter during simulation. The designLowpassFIR function redesigns the coefficients based on the updated filter specifications. Pass these updated coefficients to the FIR filter. Visualize the spectra of the input and filtered signals using the spectrum analyzer.

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Fcut = 0.5;
for idx = 1:500
    num = designLowpassFIR(FilterOrder=30,CutoffFrequency=Fcut,Window="hann");
    x = randn(1024,1);
    y = firFilt(x,num);
    spectrumScope(x,y);
    filterViz(num);
    Fcut = Fcut + 0.0005;
end

Design and implement a lowpass FIR filter object using the designLowpassFIR function. The function returns a dsp.FIRFilter object when you set the SystemObject argument to true.

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firFilt = designLowpassFIR(FilterOrder=30,CutoffFrequency=0.5,Window="hann",...
        SystemObject=true)
firFilt = 
  dsp.FIRFilter with properties:

            Structure: 'Direct form'
      NumeratorSource: 'Property'
            Numerator: [0 2.1297e-19 0.0011 -1.8613e-18 -0.0048 4.8729e-18 0.0122 -8.7270e-18 -0.0251 1.2757e-17 0.0477 -1.6267e-17 -0.0960 1.8649e-17 0.3148 0.5000 0.3148 1.8649e-17 -0.0960 -1.6267e-17 0.0477 1.2757e-17 -0.0251 ... ] (1x31 double)
    InitialConditions: 0

  Use get to show all properties

Create a dsp.DynamicFilterVisualizer object to visualize the magnitude response of the filter.

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filterViz = dsp.DynamicFilterVisualizer(NormalizedFrequency=true);
filterViz(firFilt)

Create a spectrumAnalyzer object to visualize the spectra of the input and output signals.

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spectrumScope = spectrumAnalyzer(SampleRate=44100,PlotAsTwoSidedSpectrum=false,...
    ChannelNames=["Input Signal","Filtered Signal"]);

Stream in random data and filter the signal using the dsp.FIRFilter object. Visualize the spectra of the input and filtered signals using the spectrum analyzer.

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for idx = 1:500
    x = randn(1024,1);
    y = firFilt(x);
    spectrumScope(x,y);
end

Design an equiripple FIR halfband filter with the order of 24 and a transition width of 0.1 using the designHalfbandFIR function. Assign the filter coefficients to a dsp.FIRFilter System object.

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b = designHalfbandFIR(FilterOrder=24,DesignMethod='equiripple');
hbFIR = dsp.FIRFilter(b);

Create a dsp.DynamicFilterVisualizer object and visualize the magnitude response of the filter.

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dfv = dsp.DynamicFilterVisualizer(NormalizedFrequency=true);
dfv(hbFIR);

Create a spectrumAnalyzer object to visualize the spectra of the input and output signals.

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scope = spectrumAnalyzer(SampleRate=2, PlotAsTwoSidedSpectrum=false,...
    ChannelNames=["Input Signal","Filtered Signal"]);

Stream in random data and filter the signal using the FIR halfband filter.

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for i = 1:1000
    x = randn(1024, 1);
    y = hbFIR(x);
    scope(x,y);
end

Since R2023b

Design a lowpass FIR filter using the designfilt function.

The filter is a minimum order filter with a passband frequency of 0.45 and a stopband frequency of 0.55 in normalized frequency units. The passband ripple is 1 dB and the stopband attenuation is 60 dB. Use the Kaiser window design method and set the SystemObject argument to true.

With these specifications, the designfilt function generates a dsp.FIRFilter System object™.

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lpFIRFilter = designfilt('lowpassfir', ...
    'PassbandFrequency',0.45,'StopbandFrequency',0.55, ...
    'PassbandRipple',1,'StopbandAttenuation',60, ...
    'DesignMethod','kaiserwin','SystemObject',true)
lpFIRFilter = 
  dsp.FIRFilter with properties:

            Structure: 'Direct form'
      NumeratorSource: 'Property'
            Numerator: [1.2573e-04 -1.9141e-04 -2.7282e-04 3.7207e-04 4.9141e-04 -6.3325e-04 -8.0016e-04 9.9490e-04 0.0012 -0.0015 -0.0018 0.0021 0.0025 -0.0029 -0.0034 0.0040 0.0046 -0.0053 -0.0060 0.0069 0.0079 -0.0090 -0.0102 0.0116 ... ] (1x74 double)
    InitialConditions: 0

  Use get to show all properties

Visualize the magnitude and phase responses of this filter using freqz.

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freqz(lpFIRFilter.Numerator)

Figure contains 2 axes objects. Axes object 1 with title Phase, xlabel Normalized Frequency (\times\pi rad/sample), ylabel Phase (degrees) contains an object of type line. Axes object 2 with title Magnitude, xlabel Normalized Frequency (\times\pi rad/sample), ylabel Magnitude (dB) contains an object of type line.

Algorithms

This object implements the algorithm, inputs, and outputs described on the Discrete FIR Filter (Simulink) block reference page. The object properties correspond to the block parameters.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

The dsp.FIRFilter System object supports SIMD code generation using Intel® AVX2 code replacement library under these conditions:

  • Filter structure is set to 'Direct form' or 'Direct form transposed'.

  • Input signal is real-valued with real filter coefficients.

  • When the filter structure is set to 'Direct form', the input signal can also be complex-valued with real or complex filter coefficients.

  • Input signal has a data type of single or double.

The SIMD technology significantly improves the performance of the generated code. For more information, see SIMD Code Generation. To generate SIMD code from this object, see Use Intel AVX2 Code Replacement Library to Generate SIMD Code from MATLAB Algorithms.

Version History

Introduced in R2012a

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R2023b: The designfilt function and the Design Filter Live Editor task support dsp.FIRFilter object

The designfilt function generates a dsp.FIRFilter object when you specify 'lowpassfir' and 'highpassfir' filter responses and set the 'SystemObject' flag to 'true'.

lpFIRFilter = designfilt('lowpassfir', ...
    'PassbandFrequency',0.45,'StopbandFrequency',0.55, ...
    'PassbandRipple',1,'StopbandAttenuation',60, ...
    'DesignMethod','kaiserwin','SystemObject',true)
lpFIRFilter = 
  dsp.FIRFilter with properties:

            Structure: 'Direct form'
      NumeratorSource: 'Property'
            Numerator: [1.2573e-04 -1.9141e-04 -2.7282e-04 3.7207e-04 … ] (1×74 double)
    InitialConditions: 0

The Design Filter Live Editor task generates a dsp.FIRFilter object for lowpass FIR and highpass FIR filter responses when you select the Use a System object to implement filter check box in the task UI and run the designfilt code the task generates.

See Also

Functions

Objects

Blocks

Topics