Signal Processing Toolbox

fvtool

Open the Filter Visualization Tool (FVTool)

Syntax

• fvtool(b,a)
  

fvtool(b₁,a₁,b₂,a₂,...b_n,a_n)

• fvtool(Hd1,Hd2,...)
  h = fvtool(...)
  

Description

fvtool(b,a) opens FVTool and computes the magnitude response of the digital filter defined with numerator, b and denominator, a. Using FVTool you can display the phase response, group delay, impulse response, step response, pole-zero plot, and coefficients of the filter. You can export the displayed response to a file with Export on the File menu.

fvtool(b1,a1,b2,a2,...bn,an) opens FVTool and computes the magnitude responses of multiple filters defined with numerators, b₁...b_n and denominators, a₁...a_n.

fvtool(Hd1,Hd2,...) opens FVTool and computes the magnitude responses of the filters in the dfilt objects Hd1, Hd2, etc. If you have the Filter Design Toolbox installed, you can also use fvtool(H₁,H₂,...) to analyze quantized filter (qfilt) objects, multirate filter (mfilt) objects, and adaptive filter (adaptfilt) objects.

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 below.

FVTool has two toolbars.

• Figure toolbar with the following icons
  
  

  	Start a new FVTool
  	Print file and Print preview
  	Toggle plot editing, add text, add arrow, and add line
  	Zoom in, zoom in x only, zoom in y only, and return to full view
  	Toggle legend
  	Toggle grid
  	Link to FDATool (appears only if started from FDATool)
  	Toggle Add mode/Replace mode (appears only if launched from FDATool)

• 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 on 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.
  	Superimposes the magnitude response and the phase response of the current filter. See freqz for more information.
  	Shows the 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.
  	Impluse response of the current filter. The impulse response is the response of the filter to a 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 (e.g., direct-form, lattice, etc.) in a text box.
  	Detailed filter information.

Linking to FDATool

In fdatool, selecting Full View Analysis from the Analysis menu or the Full View Analysis toolbar button 

starts FVTool for the current filter. You can synchronize FDATool and FVTool with the FDAToolLink toolbar button . Any changes made to the filter in FDATool are immediately reflected in FVTool.

Two FDATool link modes are provided via the Set Link Mode 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.

Modifying the Axes

You can change the x- or y-axis units by right-clicking the mouse on the axis label or by right-clicking on the plot and selecting Analysis Parameters. Available options for the axes units are as follows.

Plot	X-Axis Units	Y-Axis Units
Magnitude	Normalized Frequency Linear Frequency	Magnitude Magnitude(dB) Magnitude squared Zero-Phase
Phase	Normalized Frequency Linear Frequency	Phase Continuous Phase Degrees Radians
Magnitude and Phase	Normalized Frequency Linear Frequency	(y-axis on left side) Magnitude Magnitude(dB) Magnitude squared Zero-Phase (y-axis on right side) Phase Continuous Phase Degrees Radians
Group Delay	Normalized Frequency Linear Frequency	Samples Time
Phase Delay	Normalized Frequency Linear Frequency	Degrees Radians
Impulse Response	Samples Seconds	Amplitude
Step Response	Samples Time	Amplitude
Pole-Zero	Real Part	Imaginary Part

Modifying the Plot

These toolbar buttons are provided for plot editing.

• Edit Plot, Add Text, Add Arrow, Add Line allow you to change axes labels or the plot title, and add text, lines, and arrows to the plot. For detailed information see "Using Plot Editing Mode" in the Getting Started with MATLAB documentation.
• Zoom allows you to zoom the display in, zoom in x only, zoom in y only or return to full view. Zoom functions are also available from the Tools menu.
• Toggle Legend turns the legend display on or off. You can also toggle the legend using the Tools menu.
• Toggle Grid turns the grid on or off. You can also toggle the grid using the Tools menu.

Analysis Parameters are parameters that apply to the displayed analyses. To display them, right-click in the plot area and select Analysis Parameters from the menu. (Note that you can access the menu only if the Edit Plot button is inactive.) The following analysis parameters are displayed. (If more than one response is displayed, parameters applicable to each plot are displayed.) Not all of these analysis fields are displayed for all types of plots:

• Frequency Range--range of the frequency axis or Specify freq. vector
• Number of Points--number of samples used to compute the response
• Frequency Vector--vector to use for plotting, if Specify freq. vector is selected in Range.
• Frequency Units--y-axis units (Normalized or Hz)
• Frequency Scale--y-axis scale (Linear or Log)
• Phase Units--y-axis units (Degrees or Radians)
• Phase Display--type of phase plot (Phase or Continuous Phase)
• Magnitude Display--y-axis units (Magnitude, Magnitude (dB), Magnitude squared, or Zero-Phase)
• Group Delay Units--y-axis units (Samples or Time)
• Specify Length--length type of impulse or step response (Default or Specified)
• Length--number of points to use for the impulse or step response
• Time Mode--x-axis units (Samples or Seconds)

In addition to the above analysis parameters, you can change the plot type for Impulse and Step Response plots by right-clicking and selecting either Line, Stem, or Line with Markers from the menu.

To save the displayed parameters as the default values to use when FDATool or FVTool is opened, click Save as default.

To restore the MATLAB default values, click Restore orignal defaults.

Data Markers display information about a particular point in the plot. See Using Data Markers for more information.

When FVTool is started from FDATool, you can use Design Masks to display filter specifications on a Magnitude plot. See Analyzing the Filter for more information.

Overlaying a Response

You can overlay a second response on the plot by selecting Overlay Analysis from the Analysis menu 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 the x-axis and both y-axes.

Controlling FVTool from the MATLAB Command Line

After you obtain the handle for FVTool, you can control some aspects of FVTool from the command line. In addition to the standard Handle Graphics properties (see "Handle Graphics in the MATLAB documentation), FVTool has the following properties:

• 'Filters'--returns a cell array of the filters in FVTool.
• 'Analysis'--displays the specified type of analysis plot. The following table lists the analyses and corresponding analysis strings.
  
  

  Analysis Type	Analysis String
  Magnitude plot	'magnitude'
  Phase plot	'phase'
  Magnitude and Phase plot	`freq'
  Group Delay plot	'grpdelay'
  Phase Delay plot	`phasedelay'
  Impulse response plot	'impulse'
  Step response plot	'step'
  Pole-Zero plot	'polezero'
  Filter coefficients	'coefficients'
  Filter information	'info'

• 'Grid'--controls whether the grid is 'on' or 'off'
• 'Legend'--controls whether the legend is 'on' or 'off'

Note    You can change other properties of FVTool from the command line using the set function. Use get(h) to view property tags and current property settings.

You can use the following methods with the FVTool handle.

addfilter(h,filtobj) adds a new filter to FVTool. The new filter, filtobj, must be a dfilt or a Filter Design Toolbox qfilt filter object.

setfilter(h, filtobj) replaces the filter in FVTool with the filter specified in filtobj.

deletefilter(h, index) deletes the filter at the FVTool cell array index location.

legend(h,str1,str2,...) creates a legend in FVTool by associating str1 with filter 1, str2 with filter 2, etc.

For more information on using FVTool from the command line, see the demo fvtooldemo.

Examples

Example 1

Display the magnitude response of an elliptic filter, starting FVTool from the command line:

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

Example 2

Display and analyze multiple FIR filters, starting FVTool from the command line. Then, display the associated analysis parameters for the magnitude:

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

Right-click on the plot and select Analysis Parameters.

Example 3

Create a lowpass, equiripple filter of order 20 in FDATool and display it in FVTool:

• fdatool          %start FDATool
  

Set these parameters in fdatool and then click the Design Filter button.

Click the Full View Analysis button to start FVTool.

Example 4

Create an elliptic filter and use some of FVTool's figure handle commands:

• [b,a]=ellip(6,3,50,300/500);
  h = fvtool(b,a);   % Create handle, h and start FVTool
                               %    with magnitude plot
  
  
  set(h,'Analysis','phase')               % Change display to phase plot
  
  
  set(h,'Legend','on')                    % Turn legend on
  legend(h,'Phase plot')                  % Add legend text
  
  
  get(h)                                        % View all properties
                                                % FVTool-specific properties are
                                                %   at the end of this list.
  
                  AlphaMap: [1x64 double]
               BackingStore: 'off'
            CloseRequestFcn: 'closereq'
                      Color: [1x3 double]
                   ColorMap: [64x3 double]
                CurrentAxes: 564.0001
           CurrentCharacter: ''
              CurrentObject: []
               CurrentPoint: [0 0]
                  DitherMap: [64x3 double]
              DitherMapMode: 'manual'
               DoubleBuffer: 'on'
                   FileName: ''
                FixedColors: [11x3 double]
              IntegerHandle: 'on'
             InvertHardcopy: 'on'
                KeyPressFcn: ''
                    MenuBar: 'none'
                MinColormap: 64
                       Name: [1x42 char]
                   NextPlot: 'new'
                NumberTitle: 'on'
                 PaperUnits: 'inches'
           PaperOrientation: 'portrait'
              PaperPosition: [1x4 double]
          PaperPositionMode: 'manual'
                  PaperSize: [8.5000 11]
                  PaperType: 'usletter'
                    Pointer: 'arrow'
          PointerShapeCData: [16x16 double]
        PointerShapeHotSpot: [1 1]
                   Position: [360 292 560 420]
                   Renderer: 'painters'
               RendererMode: 'auto'
                     Resize: 'on'
                  ResizeFcn: ''
              SelectionType: 'normal'
                ShareColors: 'on'
                      Units: 'pixels'
        WindowButtonDownFcn: ''
      WindowButtonMotionFcn: ''
          WindowButtonUpFcn: ''
                WindowStyle: 'normal'
               BeingDeleted: 'off'
              ButtonDownFcn: ''
                   Children: [15x1 double]
                   Clipping: 'on'
                  CreateFcn: ''
                  DeleteFcn: ''
                 BusyAction: 'queue'
           HandleVisibility: 'on'
                    HitTest: 'on'
              Interruptible: 'on'
                     Parent: 0
                   Selected: 'off'
         SelectionHighlight: 'on'
                        Tag: [1x23 char]
              UIContextMenu: []
                   UserData: []
                    Visible: 'on'
            AnalysisToolbar: 'on'
              FigureToolbar: 'on'
                    Filters: {[1x1 dfilt.df2t]}
                   Analysis: 'phase'
          OverlayedAnalysis: ''
                       Grid: 'on'
                     Legend: 'off'
                 DesignMask: 'off'
             FrequencyRange: '[0, pi)'
             NumberofPoints: 8192
            FrequencyVector: [1x256 double]
             FrequencyUnits: 'Normalized'
             FrequencyScale: 'Linear'
                 PhaseUnits: 'Degrees'
               PhaseDisplay: 'Phase'
  

See Also

fdatool, sptool

freqz

gauspuls