FVTool

Filter Visualization Tool

Description

Filter Visualization Tool is an interactive app that enables you to display and analyze the responses, coefficients, and other information of a filter. You can also synchronize FVTool and Filter Designer to immediately visualize any changes made to a filter design.

In the app, you can view:

• Magnitude response

• Phase response

• Group delay

• Phase delay

• Impulse response

• Step response

• Pole-zero plot

• Filter coefficients

• Filter information

For more information, see Analysis Types.

More

If you have installed the DSP System Toolbox™, 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

Consider a 6th-order elliptic filter with 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. Display the magnitude response of the filter.

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

Magnitude and Phase Response of Bandpass FIR Filter

Design a 50th-order bandpass FIR filter with stopband frequencies of 150 Hz and 350 Hz and passband frequencies of 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")

Select the Analysis Parameters button in the toolstrip. An Analysis Parameters window appears that shows the parameters associated with the plot.

FVTool Figure Handle Commands

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. Obtain the handle for FVTool.

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

h = 
  Figure (filtervisualizationtool) with properties:

      Number: 1
        Name: 'Magnitude Response (dB)'
       Color: [0.9400 0.9400 0.9400]
    Position: [348 480 583 437]
       Units: 'pixels'

  Use get to show all properties

Use the FVTool handle to display the phase response of the filter.

h.Analysis = "phase"

h = 
  Figure (filtervisualizationtool) with properties:

      Number: 1
        Name: 'Figure 1: Phase Response'
       Color: [0.9400 0.9400 0.9400]
    Position: [1 1 1024 657]
       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: 'Phase Response'
       Color: [0.9400 0.9400 0.9400]
    Position: [1 1 1024 657]
       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'
               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: ''
                     Name: 'Phase Response'
                 NextPlot: 'new'
              NumberTitle: off
               PaperUnits: 'inches'
         PaperOrientation: 'portrait'
            PaperPosition: [-0.8700 2.2150 10.2400 6.5700]
        PaperPositionMode: 'auto'
                PaperSize: [8.5000 11]
                PaperType: 'usletter'
                  Pointer: 'arrow'
        PointerShapeCData: [16x16 double]
      PointerShapeHotSpot: [1 1]
                 Position: [1 1 1024 657]
                 Renderer: 'opengl'
             RendererMode: 'auto'
                   Resize: on
                ResizeFcn: @(~,~)fix_listbox_position(this,hFVT)
            SelectionType: 'normal'
                  ToolBar: 'none'
                     Type: 'figure'
                    Units: 'pixels'
      WindowButtonDownFcn: ''
    WindowButtonMotionFcn: ''
        WindowButtonUpFcn: ''
        WindowKeyPressFcn: ''
      WindowKeyReleaseFcn: ''
     WindowScrollWheelFcn: ''
              WindowStyle: 'docked'
             BeingDeleted: off
            ButtonDownFcn: ''
                 Children: [6x1 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
          FrequencyVector: [0 0.0039 0.0078 0.0118 0.0157 0.0196 0.0235 ... ]
      NormalizedFrequency: 'off'
           FrequencyRange: '[-Fs/2, Fs/2)'
               PhaseUnits: 'Radians'
           FrequencyScale: 'Linear'
           NumberofPoints: 8192
            PolyphaseView: 'off'
            ShowReference: 'on'
                 Analysis: 'phase'
             PhaseDisplay: 'Phase'
        OverlayedAnalysis: ''

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. For more information, see Controlling FVTool from the MATLAB Command Line.

More About

Controlling FVTool from the GUI

Display and analyze responses of one or multiple filters using controls on the toolstrip.

• By default, the app displays the magnitude response of a filter. To change the display, select an option from the Analysis list in the Analysis section of the toolstrip.

• To overlay a second response on the plot, select an available response from the Overlay Analysis list in the Analysis section of the toolstrip. The app adds a second y-axis to the right side of the response plot. The Analysis Parameters dialog box shows parameters for the x-axis and both y-axes.

• To adjust view settings, analysis parameters, or specify sampling frequency, use the corresponding buttons on the toolstrip. You can also toggle the plot legend and grid.

• To edit a plot, first click Send to Figure. In the new figure window, use the plot editing toolbar.

Analysis Types

FVTool has these analysis types:

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

Linking to Filter Designer

When the Filter Designer app displays the analysis for a filter, in the app, select View > Filter Visualization Tool or the Full View Analysis toolbar button to open FVTool for the filter. In FVTool, use the Link button to link to Filter Designer. FVTool updates the current display with any changes made to the filter in Filter Designer. By default, the app retains the current filter and adds the new filter to the display. To remove the current filter and insert the new filter, select the Replace check box in the Filter Designer section of the toolstrip.

Version History

Introduced before R2006a

R2022a: Controls are on the toolstrip

Behavior changed in R2022a

The behavior of fvtool has changed. In previous releases, the app had plot editing and analysis toolbars. Starting this release, access filter visualization controls on the toolstrip. To edit a plot, first export the plot to a figure and then use the figure controls.