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 pairs.
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.
Use FVTool to visualize a digitalFilter.
These functions take digitalFilter objects as input.

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`

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`

Examples

collapse all

Lowpass IIR Filter

Open Live Script

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.

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

Figure Magnitude Response (dB) contains an axes object. The axes object with title Magnitude Response (dB) contains 2 objects of type line.

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