Matlab filter常用函数

Posted 2020-11-17 fellow1988

 

Filtering and Analysis Functions

Filtering

Function	Description
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

Function	Description
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)

2.transform function-->zero/polo

fvtool(b,a,‘Analysis‘,‘polezero‘)

zplane(b,a)

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)

 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)

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)

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.