Filter Designer

Design filters starting with algorithm selection

Description

The Filter Designer app enables you to design and analyze digital filters. You can also import and modify existing filter designs.

Using the app, you can:

• Choose a response type and filter design method

• Set filter design specifications

• Analyze, edit, and optimize a filter design

• Export a filter design or generate MATLAB^® code

For more information, see Introduction to Filter Designer.

More

If the DSP System Toolbox™ product is installed, Filter Designer integrates advanced filter design methods and the ability to quantize filters. For more information, see filterDesigner (DSP System Toolbox).

Note

This app requires a screen resolution greater than 640 × 480.

Open the Filter Designer App

• MATLAB Toolstrip: On the Apps tab, under Signal Processing and Communications, click the app icon.

• Enter filterDesigner in the MATLAB command prompt.

Examples

FIR Bandpass Filter with Asymmetric Attenuation

Use the Filter Designer app to create a 50th-order equiripple FIR bandpass filter to be used with signals sampled at 1 kHz.

N = 50;
Fs = 1e3;

Specify that the passband spans frequencies of 200–300 Hz and that the transition region on either side has a width of 50 Hz.

Fstop1 = 150;
Fpass1 = 200;
Fpass2 = 300;
Fstop2 = 350;

Specify weights for the optimization fit:

• 3 for the low-frequency stopband

• 1 for the passband

• 100 for the high-frequency stopband

Open the Filter Designer app.

Wstop1 = 3;
Wpass = 1;
Wstop2 = 100;

filterDesigner

Use the app to design the rest of the filter. To specify the frequency constraints and magnitude specifications, use the variables you created.

1. Set Response Type to Bandpass.

2. Set Design Method to FIR. From the drop-down list, select Equiripple.

3. Under Filter Order, specify the order as N.

4. Under Frequency Specifications, specify Fs as Fs.

5. Click Design Filter.

Arbitrary Magnitude Filter

Design an FIR filter with the following piecewise frequency response:

• A sinusoid between 0 and 0.19π rad/sample.

  F1 = 0:0.01:0.19;
  A1 = 0.5+sin(2*pi*7.5*F1)/4;

• A piecewise linear section between 0.2π rad/sample and 0.78π rad/sample.

  F2 = [0.2 0.38 0.4 0.55 0.562 0.585 0.6 0.78];
  A2 = [0.5 2.3 1 1 -0.2 -0.2 1 1];

• A quadratic section between 0.79π rad/sample and the Nyquist frequency.

  F3 = 0.79:0.01:1;
  A3 = 0.2+18*(1-F3).^2;

Specify a filter order of 50. Consolidate the frequency and amplitude vectors. To give all bands equal weights during the optimization fit, specify a weight vector of all ones. Open the Filter Designer app.

N = 50;

FreqVect = [F1 F2 F3];
AmplVect = [A1 A2 A3];
WghtVect = ones(1,N/2);

filterDesigner

Use the app to design the filter.

1. Under Response Type, select the button next to Differentiator. From the drop-down list, choose Arbitrary Magnitude.

2. Set Design Method to FIR. From the drop-down list, select Least-squares.

3. Under Filter Order, specify the order as the variable N.

4. Under Frequency and Magnitude Specifications, specify the variables you created:

   • Freq. vector — FreqVect.

   • Mag. vector — AmplVect.

   • Weight vector — WghtVect.

5. Click Design Filter.

6. Right-click the y-axis of the plot and select Magnitude to express the magnitude response in linear units.

Related Examples

• Introduction to Filter Designer
• Getting Started with Filter Designer

Version History

Introduced before R2006a