fvtool (Signal Processing Toolbox)

Filter Visualization Tool

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,...b_n,a_n) opens FVTool and computes the magnitude responses of multiple filters defined with numerators, b₁...b_nand 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 objects (dfilt with arithmetic set to 'single'), 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.

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

Icon
Description

Toggle legend

Toggle grid

Link to FDATool (appears only if started from FDATool)

Toggle Add mode/Replace mode (appears only if launched from FDATool)

Icon	Description
	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.
	Shows the 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
	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. For SOS filters, each section is displayed as a separate filter.
	Detailed filter information.

Linking to FDATool

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

when an analysis is displayed 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
Time
Amplitude

Step Response
Samples
Time
Amplitude

Pole-Zero
Real Part
Imaginary Part

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 Time	Amplitude
Step Response	Samples Time	Amplitude
Pole-Zero	Real Part	Imaginary Part

Modifying the Plot

You can use any of the plot editing toolbar buttons to change the properties of your plot.

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:

Normalized Frequency -- if checked, frequency is normalized between 0 and 1, or if not checked, frequency is in Hz
Frequency Scale -- y-axis scale (Linear or Log)
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 Frequency Range.
Magnitude Display -- y-axis units (Magnitude, Magnitude (dB), Magnitude squared, or Zero-Phase)
Normalize Magnitude to 1 (0 dB) -- if checked, the magnitude is normalized so that the maximum value occurs at 1 (0 dB)
Autoscale axes -- if checked, scales the axes automatically to the data. If the Magnitude Display is not Magnitude (dB), the axes are always autoscaled. If unchecked, you can specify the y-axis (dB Display Range) as two values separated by a space.
Phase Units -- y-axis units (Degrees or Radians)
Phase Display -- type of phase plot (Phase or Continuous 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

In addition to the above analysis parameters, you can change the plot type for Impulse and Step Response plots by right-clicking and selecting Line with Marker, Stem or Line from the context menu. You can change the x-axis units by right-clicking on the x-axis label and selecting Samples or Time.

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-defined default values, click Restore original 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. You can also draw your own spectral masks. 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'`
Magnitude response estimate (available only with Filter Design Toolbox)	`'magestimate'`
Round-off noise power (available only with Filter Design Toolbox)	`'noisepower'`

'Grid' -- controls whether the grid is 'on' or 'off'
'Legend' -- controls whether the legend is 'on' or 'off'
'Fs' -- controls the sampling frequency of filters in FVTool. The sampling frequency vector must be of the same length as the number of filters or a scalar value. If it is a vector, each value is applied to its corresponding filter. If it is a scalar, the same value is applied to all filters.
SosViewSettings -- (This option is available only if you have the Filter Deisgn Toolbox.) For second-order sections filters, this controls how the filter is displayed. The SOSViewSettings property contains an object so you must use this syntax to set it: set(h.SOSViewSettings,'View',viewtype), where viewtype is one of the following:

'Complete' -- Displays the complete response of the overall filter
'Individual' -- Displays the response of each section separately
'Cumulative' -- Displays the response for each section accumulated with each prior section. If your filter has three sections, the first plot shows section one, the second plot shows the accumlation of sections one and two, and the third plot show the accumulation of all three sections.

You can also define whether to use SecondaryScaling, which determines where the sections should be split. The secondary scaling points are the scaling locations between the recursive and the nonrecursive parts of the section. The default value is false, which does not use secondary scaling. To turn on secondary scaling, use this syntax: set(h.SOSViewSettings,'View','Cumulative',true)

'UserDefined' -- Allows you to define which sections to display and the order in which to display them. Enter a cell array where each section is represented by its index. If you enter one index, only that section is plotted. If you enter a range of indices, the combined response of that range of sections is plotted. For example, if your filter has four sections, entering {1:4} plots the combined response for all four sections, and entering {1,2,3,4} plots the response for each section individually.

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 filter object. You can specify the sampling frequency of the new filter with addfilter(h,filtobj,'Fs',10)

setfilter(h,filtobj) replaces the filter in FVTool with the filter specified in filtobj. You can set the sampling frequency as described above.

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. See legend in the MATLAB documentation for information.

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 = 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);

Right-click on the plot and select Analysis Parameters..

The displayed analysis parameters are normalized frequency units, frequency range zero (exclusive) to pi (inclusive), 8192 number of points, a display-only frequency vector, linear frequency scale, and magnitude in magnitude dB.

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:

Parameter
Setting

Response Type
Lowpass

Design Method
FIR Equiripple

Filter Order
Specify order: 20

Density factor
16

Frequency specifications -- units
Normalized (0 to 1)

Wpass
0.4

Wstop
0.5

Magnitude specifications -- Wpass and Wstop
1

Parameter	Setting
`Response Type`	`Lowpass`
`Design Method`	`FIR Equiripple`
`Filter Order`	`Specify order: 20`
`Density factor`	`16`
`Frequency specifications -- units`	`Normalized (0 to 1)`
`Wpass`	`0.4`
`Wstop`	`0.5`
`Magnitude specifications -- Wpass and Wstop`	`1`

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: 'on' CloseRequestFcn: 'closereq' Color: [0.8314 0.8157 0.7843] ColorMap: [64x3 double] CurrentAxes: 208.0084 CurrentCharacter: '' CurrentObject: [] CurrentPoint: [0 0] DockControls: 'on' DoubleBuffer: 'on' FileName: '' FixedColors: [11x3 double] IntegerHandle: 'on' InvertHardcopy: 'on' KeyPressFcn: '' MenuBar: 'none' MinColormap: 64 Name: 'Filter Visualization Tool - Phase Response' NextPlot: 'new' NumberTitle: 'on' PaperUnits: 'inches' PaperOrientation: 'portrait' PaperPosition: [0.2500 2.5000 8 6] PaperPositionMode: 'manual' PaperSize: [8.5000 11] PaperType: 'usletter' Pointer: 'arrow' PointerShapeCData: [16x16 double] PointerShapeHotSpot: [1 1] Position: [360 292 560 345] Renderer: 'painters' RendererMode: 'auto' Resize: 'on' ResizeFcn: '' SelectionType: 'normal' ShareColors: 'on' Toolbar: 'auto' 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: 'filtervisualizationtool' UIContextMenu: [] UserData: [] Visible: 'on' AnalysisToolbar: 'on' FigureToolbar: 'on' Filters: {[1x1 dfilt.df2t]} Grid: 'on' Legend: 'on' DesignMask: 'off' Fs: 1 SOSViewSettings: [1x1 dspopts.sosview] Analysis: 'phase' OverlayedAnalysis: '' ShowReference: 'on' PolyphaseView: 'off' NormalizedFrequency: 'on' FrequencyScale: 'Linear' FrequencyRange: '[0, pi)' NumberofPoints: 8192 FrequencyVector: [1x256 double] PhaseUnits: 'Radians' PhaseDisplay: 'Phase'

See Also

fdatool, sptool

freqz gauspuls