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 on quantized filter (qfilt) objects by using fvtool(Hq₁,Hq₂,...).

h = fvtool(...) returns the Handle Graphics figure handle h.

	Launch a new FVTool
	Print and Print preview
	Toggle plot editing, Add text, Add arrow, and Add line
	Zoom in and Zoom out
	Toggle legend
	Display Magnitude plot
	Display Phase plot
	Display Magnitude and Phase plot
	Display Group Delay plot
	Display Impulse Response
	Display Step Response
	Display Pole-Zero plot
	Display filter coefficients
	Link to FDATool (appears only if launched from FDATool)
	Toggle Add mode/Replace mode

Linking to FDATool

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

launches 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 FDAToolLink 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
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 or out using the two zoom buttons.
• Toggle Legend allows you to turn the legend display on or off. You can also use the Edit Plot button and right-click to change the legend dispay.

Analysis Parameters are parameters that apply to the displayed analysis. 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. Not all of these analysis fields are displayed for all types of plots:

• 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.
• Response--y-axis units (Magnitude, Magnitude (dB), Magnitude squared, or Zero-Phase)
• Phase units--y-axis units (Degrees, or Radians)
• Phase--type of phase plot (Phase or Continuous Phase)
• Group Delay--y-axis units (Samples or Time)
• Frequency units--y-axis units (Normalized or Hz)
• Frequency scale--y-axis scale (Linear or Log)
• 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 Solid or Stem from the menu.

You can change the Sampling Frequency and names of your filters by right-clicking in the plot area and selecting Sampling Frequency from the menu. See Changing the Sampling Frequency for more information.

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

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:

• n = 20;                  % Filter order
  f = [0 0.4 0.5 1];       % Frequency band edges
  a = [1 1 0 0];           % Desired amplitudes 
  b  = remez(n,f,a);
  b2 = remez(n*2,f,a);     % Double the filter order
  fvtool(b,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 launch FVTool.

See Also

fdatool, sptool

freqz

gauspuls