Design a digital filter in the Live Editor
Design Filter helps you design a digital filter
interactively. The task automatically generates and runs MATLAB® code to design a filter using the
To get started, select a filter response type. The task offers controls to specify filter parameters that depend on the type of filter response and include:
Choose from a list of display options to visualize the generated filter
response and additional filter information. For a detailed description of the filter
constraints, design methods, and design method parameters, see the
For more information about Live Editor tasks, see Add Interactive Tasks to a Live Script.
To add the Design Filter task to a live script in the MATLAB Editor:
On the Live Editor tab, select Design Filter.
In a code block in the script, type a relevant keyword, such as
Design Filter from the suggested command
This example shows how to use the Design Filter task in the Live Editor to generate code for a digital filter. The task helps you interactively design a digital filter, displays the filter response, and generates code.
Create or Load Signal
In the Live Editor, load a noisy electrocardiogram (ECG) signal into the MATLAB® workspace. Plot the data.
load noisyecg plot(noisyECG_withTrend)
The ECG signal appears noisy. There are several sources of noise that can affect the signal including movement artifacts, high-frequency noise, and power source interference. Interactively design a filter to remove the noise from the signal. In the Live Editor tab, expand the Task list and select
Design Filter to open the task.
Design Lowpass FIR Filter Using Kaiser Window
To remove high-frequency noise, first select a Lowpass FIR filter and specify the Order as
10. The available options for frequency, magnitude, and algorithm parameters depend on the selected filter response type and filter order.
A lowpass filter removes from an input signal the unwanted frequency content above a specified threshold. In the Specify frequency parameters section, select
Cutoff (6dB) frequency from the Frequency constraints list. When the sample rate is known, you can select
Hz from the Frequency units list. A Sample rate option appears, and you can select a sample rate from the variables in the workspace. In this example, the sample rate is unknown, so specify a normalized cutoff frequency of
For an FIR lowpass filter, in the Specify magnitude parameters section, you can specify constraints to control the amount of passband ripple and stopband attenuation. Select
Passband ripple and stopband attenuation from the Magnitude constraints list. Magnitude constraints and filter order can also affect the transition width of the filter.
The task chooses an
FIR contrained least-squares design algorithm by default based on the specified frequency and magnitude parameters. Leave the design options at their default settings.
In the Display filter response section, select
Magnitude & phase and
Group delay to visualize the designed filter response. In the magnitude plot, you can see the level of attenuation in the stopband is at 60 dB. The group delay plot shows a delay of 5 samples and that the filter is linear phase.
Click the arrow below the Display filter response section to show the generated code for the designed filter. You can copy and paste the code on the command line to edit the filter design specifications manually.
Apply the designed filter to the noisy ECG signal. Account for the delay introduced by the filter and plot the result.
load designedFilter filteredECG = filter(designedFilter,noisyECG_withTrend); delay = grpdelay(designedFilter); mdelay = mean(delay); filteredECG(1:mdelay) = ; plot(noisyECG_withTrend(1:end-mdelay)) hold on plot(filteredECG) legend(["Original","Filtered"]) hold off
Design Equiripple Bandstop FIR Filter
A medical device like an ECG monitor can be impacted by electromagnetic interference. A power source commonly operates at a frequency of 50 Hz or 60 Hz. For this example, a 60 Hz sinusoid was added as noise to an ECG signal taken from the MIT-BIH Arrhythmia Database . The sample rate is 360 Hz. To remove the noise, open the Design Filter task and design a minimum-order bandstop FIR filter. Change the default filter name to
Specify the Frequency units as
Hz. To specify a sample rate, enter a value or select a sample rate variable from the list. To appear in the list, a sample rate variable must be saved in the workspace. Create a variable,
fs, and set it equal to
360 Hz, then select
fs from the Sample rate list. Specify the passband and stopband frequency values to attenuate frequencies between 55–65 Hz for a 10 Hz notch filter centered at 60 Hz.
fs = 360;
Set the Passband ripple 2 (dB) to
0.5 and increase the Stopband attenuation (dB) to
The task defaults to an equiripple design method. Display the magnitude and phase responses of the filter.
You can also select
Filter information from the Display filter response section to view additional details about the designed filter.
ecg60Hz into the workspace. The MAT-file contains the original ECG signal with added noise (
ecg60) and the filtered signal (
ecgFilt). Plot both signals to visualize the filter result.
load ecg60Hz t = 0:1/fs:(length(ecg60)-1)/fs; plot(t,[ecg60 ecgFilt]) legend(["Original";"Filtered"])
Filter response— Filter response type
Hilbert Transformer FIR|
Choose the filter response type as one of these:
Hilbert Transformer FIR
Filter Order— Filter order
Design a minimum order filter or specify a filter order. Some responses might not have a minimum order design available and will require you to specify a filter order value.
Frequency constraints— Frequencies at which filter exhibits desired behavior
Passband and stopband frequencies|
Cutoff (6dB) frequency|
Half power (3dB) frequency| ...
Specify the frequencies at which the designed filter exhibits a desired behavior. Available options depend on filter response type and filter order.
You can specify Frequency units as
to 1) (default) or
Hz. If you specify frequency units
in hertz, you must specify a sample rate.
Magnitude constraints— Filter magnitude response behavior at particular frequency ranges
Stopband attenuation| ...
Choose the filter magnitude response behavior at the specified frequency ranges. Available options depend on filter response type, filter order, and frequency constraints.
Design method— Filter design algorithm
FIR least-squares| ...
Specify the algorithm used to design the filter. Available options depend on filter response type, filter order, and frequency and magnitude constraints. Some design methods have additional options available in the Design options section.
In some design cases, there are model order restrictions. If an even or odd restriction exists for the selected design method and the specified order is not valid, the task reduces the order by one.
You can toggle the autorun option by clicking the circle in the top right corner of the task window. If autorun is enabled, the current section including the task runs automatically when a change is made.
 Moody, G.B., and R.G. Mark. "The Impact of the MIT-BIH Arrhythmia Database". IEEE Eng in Med and Biol 20(3):45-50 (May-June 2001): 45-50.