FVTool

Filter Visualization Tool

Description

Filter Visualization Tool is an interactive tool that enables you to display the magnitude, phase response, group delay, impulse response, step response, pole-zero plot, and coefficients of a filter. You can export the displayed response to a file with File > Export.

More

If the DSP System Toolbox™ product is installed, FVTool can also visualize the frequency response of a filter System object™. If you need to filter streaming data in real time, using System objects is the recommended approach. For more information, see fvtool (DSP System Toolbox).

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Open the FVTool

FVTool can be opened programmatically using one of the methods described in Programmatic Use.

Examples

Magnitude Response of Elliptic Filter

Display the magnitude response of a 6th-order elliptic filter. Specify a passband ripple of 3 dB, a stopband attenuation of 50 dB, a sample rate of 1 kHz, and a normalized passband edge of 300 Hz. Start FVTool from the command line.

[b,a] = ellip(6,3,50,300/500);
fvtool(b,a)

Display Analysis Parameters

Display and analyze multiple FIR filters, starting FVTool from the command line.

b1 = firpm(20,[0 0.4 0.5 1],[1 1 0 0]); 
b2 = firpm(40,[0 0.4 0.5 1],[1 1 0 0]); 
fvtool(b1,1,b2,1)

Display the associated analysis parameters by selecting Analysis > Analysis Parameters.

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FVTool Figure Handle Commands

Start FVTool from the command line. Display the magnitude response of a 6th-order elliptic filter. Specify a passband ripple of 3 dB, a stopband attenuation of 50 dB, a sample rate of 1 kHz, and a normalized passband edge of 300 Hz.

[b,a] = ellip(6,3,50,300/500);
h = fvtool(b,a)

h = 
  Figure (filtervisualizationtool) with properties:

      Number: 1
        Name: 'Filter Visualization Tool - Magnitude Response (dB)'
       Color: [0.9400 0.9400 0.9400]
    Position: [346.5000 282.5000 583 437]
       Units: 'pixels'

  Use get to show all properties

Display the phase response of the filter.

h.Analysis = 'phase'

h = 
  Figure (filtervisualizationtool) with properties:

      Number: 1
        Name: 'Filter Visualization Tool - Phase Response'
       Color: [0.9400 0.9400 0.9400]
    Position: [346.5000 282.5000 583 437]
       Units: 'pixels'

  Use get to show all properties

Turn on the plot legend and add text.

legend(h,'Phase plot')

Specify a sample rate of 1 kHz. Display the two-sided centered response.

h.Fs = 1000;
h.FrequencyRange='[-Fs/2, Fs/2)'

h = 
  Figure (filtervisualizationtool) with properties:

      Number: 1
        Name: 'Filter Visualization Tool - Phase Response'
       Color: [0.9400 0.9400 0.9400]
    Position: [346.5000 282.5000 583 437]
       Units: 'pixels'

  Use get to show all properties

View the all the properties of the plot. The properties specific to FVTool are at the end of the list.

get(h)

                     Grid: on
                   Legend: 'on'
          AnalysisToolbar: 'on'
            FigureToolbar: 'on'
               DesignMask: 'off'
          SOSViewSettings: [1x1 dspopts.sosview]
                       Fs: 1000
                 Alphamap: [0 0.0159 0.0317 0.0476 0.0635 0.0794 0.0952 ... ]
          CloseRequestFcn: 'closereq'
                    Color: [0.9400 0.9400 0.9400]
                 Colormap: [256x3 double]
              ContextMenu: [0x0 GraphicsPlaceholder]
              CurrentAxes: [1x1 Axes]
         CurrentCharacter: ''
            CurrentObject: [0x0 GraphicsPlaceholder]
             CurrentPoint: [0 0]
             DockControls: on
                 FileName: ''
            IntegerHandle: on
           InvertHardcopy: on
              KeyPressFcn: ''
            KeyReleaseFcn: ''
                  MenuBar: 'none'
                     Name: 'Filter Visualization Tool - Phase Response'
                 NextPlot: 'new'
              NumberTitle: on
               PaperUnits: 'inches'
         PaperOrientation: 'portrait'
            PaperPosition: [1.3350 3.3150 5.8300 4.3700]
        PaperPositionMode: 'auto'
                PaperSize: [8.5000 11]
                PaperType: 'usletter'
                  Pointer: 'arrow'
        PointerShapeCData: [16x16 double]
      PointerShapeHotSpot: [1 1]
                 Position: [346.5000 282.5000 583 437]
                 Renderer: 'opengl'
             RendererMode: 'auto'
                   Resize: on
                ResizeFcn: ''
            SelectionType: 'normal'
                  ToolBar: 'auto'
                     Type: 'figure'
                    Units: 'pixels'
      WindowButtonDownFcn: ''
    WindowButtonMotionFcn: ''
        WindowButtonUpFcn: ''
        WindowKeyPressFcn: ''
      WindowKeyReleaseFcn: ''
     WindowScrollWheelFcn: ''
              WindowStyle: 'normal'
             BeingDeleted: off
            ButtonDownFcn: ''
                 Children: [15x1 Graphics]
                 Clipping: on
                CreateFcn: ''
                DeleteFcn: ''
               BusyAction: 'queue'
         HandleVisibility: 'on'
                  HitTest: on
            Interruptible: on
                   Parent: [1x1 Root]
                 Selected: off
       SelectionHighlight: on
                      Tag: 'filtervisualizationtool'
                 UserData: []
                  Visible: on
           NumberofPoints: 8192
      NormalizedFrequency: 'off'
           FrequencyScale: 'Linear'
                 Analysis: 'phase'
           FrequencyRange: '[-Fs/2, Fs/2)'
               PhaseUnits: 'Radians'
          FrequencyVector: [0 0.0039 0.0078 0.0118 0.0157 0.0196 0.0235 ... ]
             PhaseDisplay: 'Phase'
            PolyphaseView: 'off'
        OverlayedAnalysis: ''
            ShowReference: 'on'

Magnitude and Phase Response of Bandpass FIR Filter

Design a 50th-order bandpass FIR filter with stopband frequencies 150 Hz and 350 Hz and passband frequencies 200 Hz and 300 Hz. The sample rate is 1000 Hz. Visualize the magnitude and phase response of the filter.

N = 50;
Fstop1 = 150;
Fstop2 = 350;

Fpass1 = 200;
Fpass2 = 300;

Fs = 1e3;

bpFilt = designfilt('bandpassfir','FilterOrder',N, ...
'StopbandFrequency1',Fstop1,...
'StopbandFrequency2',Fstop2,...
'PassbandFrequency1',Fpass1,...
'PassbandFrequency2',Fpass2,...
'SampleRate',Fs);

fvtool(bpFilt,'Analysis','freq')

Related Examples

• Filter Analysis Using FVTool

Programmatic Use

fvtool(b,a)

fvtool(b,a) opens FVTool and displays the magnitude response of the digital filter defined with numerator b and denominator a. Specify b and a coefficients in ascending order of power z^-1.

fvtool(sos)

fvtool(sos) opens FVTool and displays the magnitude response of the digital filter defined by the L-by-6 matrix of second order sections:

$$\text{sos}=\left[\begin{array}{cccccc}{b}_{01}& b_{11}& b_{21}& 1& a_{11}& a_{21}\\ b_{02}& b_{12}& b_{22}& 1& a_{12}& a_{22}\\ ⋮& ⋮& ⋮& ⋮& ⋮& ⋮\\ b_{0L}& b_{1L}& b_{2L}& 1& a_{1L}& a_{2L}\end{array}\right]$$

The rows of sos contain the numerator and denominator coefficients b_ik and a_ik of the cascade of second-order sections of H(z):

$$H(z)=g{\displaystyle \prod _{k=1}^L{H}_k}(z)=g{\displaystyle \prod _{k=1}^L\frac{b_{0k}+b_{1k}{z}^{-1}+b_{2k}{z}^{-2}}{1+a_{1k}{z}^{-1}+a_{2k}{z}^{-2}}}.$$

The number of sections, L, must be greater than or equal to 2. If the number of sections is less than 2, fvtool considers the input to be a numerator vector.

fvtool(d)

fvtool(d) opens FVTool and displays the magnitude response of a digital filter, d. Use designfilt to generate d based on frequency-response specifications.

fvtool(b1,a1,b2,a2,...,bN,aN)

fvtool(b1,a1,b2,a2,...,bN,aN) opens FVTool and displays the magnitude responses of multiple filters defined with numerators b1, …, bN and denominators a1, ..., aN.

fvtool(sos1,sos2,...,sosN)

fvtool(sos1,sos2,...,sosN) opens FVTool and displays the magnitude responses of multiple filters defined with second order section matrices sos1, sos2, ..., sosN.

fvtool(Hd)

fvtool(Hd) opens FVTool and displays the magnitude responses for the dfilt filter object Hd or the array of dfilt filter objects.

fvtool(Hd1,Hd2,...,HdN)

fvtool(Hd1,Hd2,...,HdN) opens FVTool and displays the magnitude responses of the filters in the dfilt objects Hd1, Hd2, ..., HdN.

h = fvtool(___)

h = fvtool(___) returns a figure handle h. You can use this handle to interact with FVTool from the command line. See Controlling FVTool from the MATLAB Command Line.

More About

Controlling FVTool from the GUI

FVTool has two toolbars:

• An extended version of the MATLAB^® plot editing toolbar. The following table shows the toolbar icons specific to FVTool:

  Icon	Description
  	Restore default view. This view displays buffer regions around the data and shows only significant data. To see the response using standard MATLAB plotting, which shows all data values, use View > Full View.
  	Toggle legend
  	Toggle grid
  	Link to Filter Designer (appears only if FVTool was started from Filter Designer)
  	Toggle Add mode/Replace mode (appears only if FVTool was launched from Filter Designer)

• Analysis toolbar with the following icons:

  	Magnitude response of the current filter. See freqz and zerophase for more information. To see the zero-phase response, right-click the y-axis label of the Magnitude plot and select Zero-phase from the context menu.
  	Phase response of the current filter. See phasez for more information.
  	Magnitude response and the phase response of the current filter superimposed on one another. See freqz for more information.
  	Group delay of the current filter. Group delay is the average delay of the filter as a function of frequency. See grpdelay for more information.
  	Phase delay of the current filter. Phase delay is the time delay the filter imposes on each component of the input signal. See phasedelay for more information.
  	Impulse response of the current filter. The impulse response is the response of the filter to an impulse input. See impz for more information.
  	Step response of the current filter. The step response is the response of the filter to a step input. See stepz for more information.
  	Pole-zero plot, which shows the pole and zero locations of the current filter on the z-plane. See zplane for more information.
  	Filter coefficients of the current filter, which depend on the filter structure (direct-form or lattice) in a text box. For SOS filters, each section is displayed as a separate filter.
  	Detailed filter information.

Linking to Filter Designer

In the Filter Designer app, selecting View > Filter Visualization Tool or the Full View Analysis toolbar button when an analysis is displayed starts FVTool for the current filter. You can synchronize Filter Designer and FVTool with the toolbar button. Any changes made to the filter in Filter Designer are immediately reflected in FVTool.

Two link modes are provided via the toggle toolbar button  / :

• Replace — removes the filter currently displayed in FVTool and inserts the new filter.

• Add — retains the filter currently displayed in FVTool and adds the new filter to the display.

Overlaying a Response

You can overlay a second response on the plot by selecting Analysis > Overlay Analysis and selecting an available response. A second y-axis is added to the right side of the response plot. The Analysis Parameters dialog box shows parameters for thex-axis and both y-axes. See Display Analysis Parameters for a sample Analysis Parameters dialog box.