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Matlab filter常用函數

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Filtering and Analysis Functions

Filtering

FunctionDescription

fftfilt

Filters a signal with a digitalFilter using an FFT-based overlap-add method

filter

Filters a signal using a digitalFilter

filtfilt

Performs zero-phase filtering of a signal with a digitalFilter

Filter Analysis

FunctionDescription

double

Casts the coefficients of a digitalFilter to double precision

filt2block

Generates a Simulink? filter block corresponding to a digitalFilter

filtord

Returns the filter order of a digitalFilter

firtype

Returns the type (1, 2, 3, or 4) of an FIR digitalFilter

freqz

Returns or plots the frequency response of a digitalFilter

fvtool

Opens the Filter Visualization Tool and displays the magnitude response of a digitalFilter

grpdelay

Returns or plots the group delay response of a digitalFilter

impz

Returns or plots the impulse response of a digitalFilter

impzlength

Returns the length of the impulse response of a digitalFilter, whether actual (for FIR filters) or effective (for IIR filters)

info

Returns a character array with information about a digitalFilter

isallpass

Returns true if a digitalFilter is allpass

isdouble

Returns true if the coefficients of a digitalFilter are double precision

isfir

Returns true if a digitalFilter has a finite impulse response

islinphase

Returns true if a digitalFilter has linear phase

ismaxphase

Returns true if a digitalFilter is maximum phase

isminphase

Returns true if a digitalFilter is minimum phase

issingle

Returns true if the coefficients of a digitalFilter are single precision

isstable

Returns true if a digitalFilter is stable

phasedelay

Returns or plots the phase delay response of a digitalFilter

phasez

Returns or plots the (unwrapped) phase response of a digitalFilter

single

Casts the coefficients of a digitalFilter to single precision

ss

Returns the state-space representation of a digitalFilter

stepz

Returns or plots the step response of a digitalFilter

tf

Returns the transfer function representation of a digitalFilter

zerophase

Returns or plots the zero-phase response of a digitalFilter

zpk

Returns the zero-pole-gain representation of a digitalFilter

zplane

Displays the poles and zeros of the transfer function represented by a digitalFilter

1.zero,pole-->transfer function form

[b,a] = zp2tf(zer,pol,1);
fvtool(b,a)

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2.transform function-->zero/polo

fvtool(b,a,‘Analysis‘,‘polezero‘)

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zplane(b,a)

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3.Z-transform frequency response of a digital filter.

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

returns the p-point complex frequency response, H(ejω), of the digital filter.

For example, a ninth-order Butterworth lowpass filter with a cutoff frequency of 400 Hz, based on a 2000 Hz sampling frequency, is

[b,a] = butter(9,400/1000);

To calculate the 256-point complex frequency response for this filter, and plot the magnitude and phase with freqz, use

freqz(b,a,256,2000)

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4.filter

Use filter in the form y = filter(d,x) to filter an input signal, x, with a digitalFilter, d, and obtain output data, y.

5.designfilt(https://ww2.mathworks.cn/help/signal/ref/designfilt.html)

Use designfilt in the form d = designfilt(resp,Name,Value) to design a digital filter, d, with response type resp. Specify the filter further using a set of Name,Value pairs.

Type d.Coefficients to obtain the coefficients of a digitalFilter, d. For IIR filters, the coefficients are expressed as second-order sections.

Lowpass IIR Filter

Design a lowpass IIR filter with order 8, passband frequency 35 kHz, and passband ripple 0.2 dB. Specify a sample rate of 200 kHz. Visualize the magnitude response of the filter. Use it to filter a 1000-sample random signal.

lpFilt = designfilt(‘lowpassiir‘,‘FilterOrder‘,8, ...
         ‘PassbandFrequency‘,35e3,‘PassbandRipple‘,0.2, ...
         ‘SampleRate‘,200e3);
fvtool(lpFilt)

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dataIn = randn(1000,1);
dataOut = filter(lpFilt,dataIn);

Output the filter coefficients, expressed as second-order sections.

sos = lpFilt.Coefficients
sos = 4×6

    0.2666    0.5333    0.2666    1.0000   -0.8346    0.9073
    0.1943    0.3886    0.1943    1.0000   -0.9586    0.7403
    0.1012    0.2023    0.1012    1.0000   -1.1912    0.5983
    0.0318    0.0636    0.0318    1.0000   -1.3810    0.5090

Bandpass FIR Filter

Design a 20th-order bandpass FIR filter with lower cutoff frequency 500 Hz and higher cutoff frequency 560 Hz. The sample rate is 1500 Hz. Visualize the magnitude response of the filter. Use it to filter a random signal containing 1000 samples.

bpFilt = designfilt(‘bandpassfir‘,‘FilterOrder‘,20, ...
         ‘CutoffFrequency1‘,500,‘CutoffFrequency2‘,560, ...
         ‘SampleRate‘,1500);
fvtool(bpFilt)

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dataIn = randn(1000,1);
dataOut = filter(bpFilt,dataIn);

Output the filter coefficients.

b = bpFilt.Coefficients
b = 1×21

   -0.0113    0.0067    0.0125   -0.0445    0.0504    0.0101   -0.1070    0.1407   -0.0464   -0.1127    0.1913   -0.1127   -0.0464    0.1407   -0.1070    0.0101    0.0504   -0.0445    0.0125    0.0067   -0.0113 ?

6.fvtool

fvtool(b,a)
fvtool(sos)
fvtool(d)
fvtool(b1,a1,b2,a2,...,bN,aN)
fvtool(sos1,sos2,...,sosN)
fvtool(Hd)
fvtool(Hd1,Hd2,...,HdN)
h = fvtool(...)

Use fvtool to visualize a digitalFilter, d.

Matlab filter常用函數