Open Filter Visualization Tool
h = fvtool(...)
fvtool(b,a) opens FVTool
and displays the magnitude response of the digital filter defined
b and denominator,
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 File > Export.
If the input to
fvtool is single precision,
the magnitude response is calculated using single-precision arithmetic.
fvtool(sos) opens FVTool and displays the magnitude response of the
digital filter defined by the L-by-6 matrix of second order
The rows of sos contain the numerator and denominator coefficients bik and aik of the cascade of second-order sections of H(z):
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) opens FVTool and displays the
magnitude response of a digital filter,
designfilt to generate
on frequency-response specifications.
FVTool and displays the magnitude responses of multiple filters defined
fvtool(sos1,sos2,...,sosN) opens FVTool
and displays the magnitude responses of multiple filters defined with
second order section matrices,
fvtool(Hd) opens FVTool and displays the magnitude
responses for the
dfilt filter object,
the array of
dfilt filter objects.
fvtool(Hd1,Hd2,...,HdN) opens FVTool and displays the
magnitude responses of the filters in the
If you have the DSP System
Toolbox™ product installed,
you can also use
Quantized filter objects (
dfilt with arithmetic set
Any of the following filter System objects.
The following Filter System objects are supported by this analysis function:
|Filter System objects|
When the input filter is a
dfilt object, FVTool performs fixed-point
analysis if the arithmetic property of the filter object is set to
'fixed'. However, for filter System objects,
based on the arithmetic specified in the
ARITH can be one of
'Arithmetic' input is only relevant for the analysis of filter
System objects. The arithmetic setting
ARITH, applies to all the
filter System objects that you input to FVTool. When you specify
'single', the function performs
double- or single-precision analysis. When you specify
'fixed' , the
arithmetic changes depending on the setting of the
CoefficientDataType property and whether the System object is
locked or unlocked.
If you do not specify the arithmetic for non-CIC structures, and the System object is in an unlocked state, the function uses double-precision arithmetic. If the System object is locked, the function performs analysis based on the locked input data type. CIC structures only support fixed-point arithmetic.
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.
FVTool has two toolbars.
An extended version of the MATLAB® plot editing toolbar. The following table shows the toolbar icons specific to FVTool.
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 Add mode/Replace mode (appears only if FVTool was launched from Filter Designer)
Analysis toolbar with the following icons
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
Superimposes the magnitude response and the phase response
of the current filter. See
Shows the group delay of the current filter. Group delay
is the average delay of the filter as a function of frequency. See
Shows the phase delay of the current filter. Phase delay
is the time delay the filter imposes on each component of the input
Impulse response of the current filter. The impulse response
is the response of the filter to a impulse input. See
Step response of the current filter. The step response
is the response of the filter to a step input. See
Pole-zero plot, which shows the pole and zero locations
of the current filter on the z-plane. See
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.
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.
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 and Phase
(y-axis on left side)
(y-axis on right side)
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
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
Phase Units — y-axis
Phase Display — type of
phase plot (
Group Delay Units — y-axis
Specify Length — length
type of impulse or step response (
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 the x-axis label and selecting
To save the displayed parameters as the default values to use when Filter Designer or FVTool is opened, click Save as default.
To restore the default values, click Restore original defaults.
Data tips display information about a particular point in the plot. See Interactively Explore Plotted Data (MATLAB) for information on data tips.
If you have the DSP System Toolbox software, FVTool displays a specification mask along with your designed filter on a magnitude plot.
To use View > Passband zoom, your filter must have been designed using
fdesign or Filter Designer. Passband zoom is not
provided for cascaded integrator-comb (CIC) filters because CICs do not have
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 the x-axis and both y-axes. See Display Analysis Parameters for a sample Analysis Parameters dialog box.
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:
'Analysis' — displays the
specified type of analysis plot. The following table lists all analysis
types and how to invoke them. Note that the only analyses that use
filter internals are magnitude response estimate and round-off noise
power, which are available only with the DSP System
|Analysis Type||Analysis Option|
Magnitude and phase plot
Group delay plot
Phase delay plot
Impulse response plot
Step response plot
Magnitude response estimate
with the DSP System
Toolbox product, see
Round-off noise power
(available only with
the DSP System
Toolbox product, see
'Grid' — controls whether
the grid is
'Legend' — controls whether
the legend is
'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.
(This option is available only if you have the DSP System
For second-order sections filters, this controls how the filter is
SOSViewSettings property contains
an object so you must use this syntax to set it:
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 accumulation of sections one and two, and the third plot show the accumulation of all three sections.
You can also define whether to use
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
which does not use secondary scaling. To turn on secondary scaling,
use this syntax:
'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
the combined response for all four sections, and entering
the response for each section individually.
You can change other properties of FVTool from the command line
set function. Use
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
setfilter(h,filtobj) replaces the filter
in FVTool with the filter specified in
You can set the sampling frequency as described above.
deletefilter(h, index) deletes the filter
at the FVTool cell array
legend(h,str1,str2,...) creates a legend
in FVTool by associating
str1 with filter 1,
filter 2, etc. See
the MATLAB documentation for information.
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 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.
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);
Display the phase response of the filter.
h.Analysis = 'phase';
Turn on the plot legend and add text.
Specify a sample rate of 1 kHz. Display the two-sided centered response.
h.Fs = 1000; h.FrequencyRange='[-Fs/2, Fs/2)';
View the all the properties of the plot. The properties specific to FVTool are at the end of the list.
Grid: 'on' Legend: 'on' AnalysisToolbar: 'on' FigureToolbar: 'on' DesignMask: 'off' SOSViewSettings: [1x1 dspopts.sosview] Fs: 1000 Alphamap: [1x64 double] CloseRequestFcn: 'closereq' Color: [0.9400 0.9400 0.9400] Colormap: [64x3 double] 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' UIContextMenu: [0x0 GraphicsPlaceholder] UserData:  Visible: 'on' FrequencyScale: 'Linear' FrequencyVector: [1x256 double] PolyphaseView: 'off' OverlayedAnalysis: '' Analysis: 'phase' NumberofPoints: 8192 FrequencyRange: '[-Fs/2, Fs/2)' NormalizedFrequency: 'off' PhaseUnits: 'Radians' PhaseDisplay: 'Phase' ShowReference: 'on'