digitalFilter

Digital filter

Description

Use designfilt to design and edit digitalFilter objects.

• Use designfilt in the form d = designfilt(resp,Name,Value) to design a digital filter d with response type resp. Customize the filter further using name-value arguments.

• Use designfilt in the form designfilt(d) to edit an existing filter, d.

  Note

  This is the only way to edit an existing digitalFilter object. Its properties are otherwise read-only.

• Use filter in the form dataOut = filter(d,dataIn) to filter a signal with a digitalFilter d. The input can be a double- or single-precision vector. It can also be a matrix with as many columns as there are input channels. You can also use the filtfilt and fftfilt functions with digitalFilter objects.

• Use Filter Analyzer to visualize a digitalFilter.

Object 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
bandpass	Bandpass-filters a signal using a digitalFilter and compensates for the delay introduced by the filter
bandstop	Bandstop-filters a signal using a digitalFilter and compensates for the delay introduced by the filter
highpass	Highpass-filters a signal using a digitalFilter and compensates for the delay introduced by the filter
lowpass	Lowpass-filters a signal using a digitalFilter and compensates for the delay introduced by the filter

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
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

Examples

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 frequency response of the filter.

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

Use the filter you designed to filter a 1000-sample random signal.

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

Version History

Introduced in R2014a