dsp.DynamicFilterVisualizer

Display time-varying magnitude and phase response of digital filters

Description

The dsp.DynamicFilterVisualizer object displays the magnitude response and phase response of time-varying digital filters or time-varying filter coefficients. The input to this object can be a filter coefficients vector or a filter System object™.

Using the dynamic filter visualizer, you can configure the plot settings, find the peak values, enable cursor measurements, and even generate script to recreate the plot with the current settings from the visualizer interface. For details, see Configure Filter Visualizer.

Creation

Syntax

dfv = dsp.DynamicFilterVisualizer

dfv = dsp.DynamicFilterVisualizer(nfft)

dfv = dsp.DynamicFilterVisualizer(nfft,Fs)

dfv = dsp.DynamicFilterVisualizer(nfft,Fs,range)

dfv = dsp.DynamicFilterVisualizer(Name=Value)

Description

dfv = dsp.DynamicFilterVisualizer returns a dynamic filter visualizer object, dfv, that displays the magnitude response of digital filters or filter coefficients.

dfv = dsp.DynamicFilterVisualizer(nfft) returns a dynamic filter visualizer with the FFTLength property set to nfft.

dfv = dsp.DynamicFilterVisualizer(nfft,Fs) returns a dynamic filter visualizer with the FFTLength property set to nfft and the SampleRate property set to Fs.

dfv = dsp.DynamicFilterVisualizer(nfft,Fs,range) returns a dynamic filter visualizer with the FFTLength property set to nfft, the SampleRate property set to Fs, and the FrequencyRange property set to range.

dfv = dsp.DynamicFilterVisualizer(Name=Value) returns a dynamic filter visualizer with each specified property set to the specified value. You can specify name-value pair arguments in any order.

Properties

Frequently Used

FFTLength — FFT length

2048 (default) | positive integer

FFT length that the dynamic filter visualizer uses to compute spectral estimates, specified as a positive integer.

Tunable: Yes

Scope Window Use

In the Configuration section on the Plot tab of the Dynamic Filter Visualizer toolstrip, click Settings. In the Filter Visualizer Settings window that opens, under Data and Axes, set FFT Length to a positive integer.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

NormalizedFrequency — Flag to display normalized frequency

false (default) | true

Since R2023a

Flag to display normalized frequency, specified as one of these values:

• true –– The filter visualizer displays the frequency response in normalized frequency units (0 to 1).

• false –– The filter visualizer displays the frequency response in Hz. You can specify the input sample rate through the SampleRate property.

Data Types: logical

SampleRate — Sampling rate of input

44100 (default) | positive scalar

Sampling rate of the input signal, specified as a real positive scalar in Hz.

Tunable: Yes

Dependency

To enable this property, set NormalizedFrequency to false. (since R2023a)

Scope Window Use

On the Plot tab, in the Configuration section, click Settings. In the Filter Visualizer Settings window, under Data and Axes, set Sample Rate (Hz) to a positive scalar.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

FrequencyRange — Range of frequency axis

[0 22050] (default) | two-element numeric vector

Range of the frequency axis, specified as a two-element numeric vector that is monotonically increasing and of the form [fmin, fmax].

• When you set the NormalizedFrequency property to true, fmax is in normalized frequency units and must be a positive scalar that is less than or equal to 1. (since R2023a)

• When you set the NormalizedFrequency property to false, fmax is in Hz and must be less than or equal to Fs/2, where Fs is the value you specify in the SampleRate property. (since R2023a)

Tunable: Yes

Scope Window Use

On the Plot tab, in the Configuration section, click Settings. In the Filter Visualizer Settings window, under Data and Axes, set Frequency Range to a two-element numeric vector.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

XScale — x-axis scale

'Log' (default) | 'Linear'

X-axis scale, specified as either 'Linear' or 'Log'.

Tunable: Yes

Scope Window Use

In the Configuration section on the Plot tab of the Dynamic Filter Visualizer toolstrip, click Settings. In the Filter Visualizer Settings window that opens, under Data and Axes, set X-Scale to Linear or Log.

MagnitudeDisplay — y-axis units

'Magnitude (dB)' (default) | 'Magnitude'|'Magnitude squared'

Y-axis units, specified as one of the following:

• 'Magnitude'

• 'Magnitude (dB)'

• 'Magnitude squared'

Tunable: Yes

Scope Window Use

In the Configuration section on the Plot tab of the Dynamic Filter Visualizer toolstrip, click Settings. In the Filter Visualizer Settings window that opens, under Data and Axes, set Display Unit to Magnitude, Magnitude (dB), or Magnitude Squared.

PlotAsMagnitudePhase — Plot magnitude and phase response of filter

false (default) | true

• true – The filter visualizer plots the magnitude and phase responses of the filter on two separate axes.

• false – The filter visualizer plots only the magnitude response of the filter.

Tunable: Yes

Scope Window Use

In the Configuration section on the Plot tab of the Dynamic Filter Visualizer toolstrip, click the Magnitude Phase button.

PlotType — Option to control type of plot

"Line" (default) | "Stairs" | "Stem"

Specify the type of plot to use in the filter visualizer window as one of these:

• "Line" – The filter visualizer connects each point on the magnitude and phase response plot with a line.

• "Stairs" – The filter visualizer displays the filter response (magnitude, phase, or both) as a stair-step graph. A stair-step graph is made up of only horizontal lines and vertical lines. Each horizontal line represents the filter response over a frequency value and is connected to two vertical lines. Each vertical line represents a change in values occurring at a frequency.

• "Stem" – The filter visualizer displays the frequency response as circles with vertical lines extending down to the x-axis at each of the frequency values.

Tunable: Yes

Scope Window Use

In the Configuration section on the Plot tab of the Dynamic Filter Visualizer toolstrip, click Settings. In the Filter Visualizer Settings window that opens, under Data and Axes, set Plot Type to Line, Stairs, or Stem.

AxesScaling — Axes scaling mode

"OnceAtStop" (default) | "Auto" | "Manual" | "Updates"

Specify the scaling mode for the axes as one of these:

• "Auto" — The filter visualizer scales the axes as needed to fit the data, both during and after simulation.

• "Manual" — The filter visualizer does not scale the axes automatically.

• "OnceAtStop" — The filter visualizer scales the axes when the simulation stops.

• "Updates" — The filter visualizer scales the axes limits once after a set number of visual updates. The number of updates is determined by the value of the AxesScalingNumUpdates property.

Tunable: Yes

Scope Window Use

Hover over the filter visualizer to see the maximize , pan , zoom , and autoscale buttons. You can also zoom and pan using your mouse.

Data Types: char | string

AxesScalingNumUpdates — Number of updates before scaling

100 (default) | real positive integer

Specify the number of updates before scaling as a real, positive scalar integer.

Tunable: Yes

Dependency

To enable this property, set AxesScaling to "Updates".

Data Types: double

Measurements

MeasurementChannel — Channel for which to obtain measurements

1 (default) | positive integer

Channel for which to obtain measurements, specified as a positive integer in the range [1 N], where N is the number of input channels.

Tunable: Yes

Scope Window Use

Click the Measurements tab on the Dynamic Filter Visualizer toolstrip. In the Channel section, select a Channel.

Data Types: double

CursorMeasurements — Cursor measurements

CursorMeasurementsConfiguration object

Cursor measurements to display waveform cursors, specified as a CursorMeasurementsConfiguration object.

All CursorMeasurementsConfiguration properties are tunable.

Tunable: Yes

Scope Window Use

Click the Measurements tab on the Dynamic Filter Visualizer toolstrip and modify the cursor measurements in the Cursors section.

PeakFinder — Peak finder measurements

PeakFinderConfiguration object

Peak finder measurements to compute and display the largest calculated peak values, specified as a PeakFinderConfiguration object.

All PeakFinderConfiguration properties are tunable.

Tunable: Yes

Scope Window Use

Click the Measurements tab on the Dynamic Filter Visualizer toolstrip and modify the peak finder measurements in the Peaks section.

Visualization

Name — Caption to display on Dynamic Filter Visualizer window

'Dynamic Filter Visualizer' (default) | character vector | string scalar

Caption to display on the Dynamic Filter Visualizer window, specified as a character vector or a string scalar.

Example: 'Dynamic Filter Visualizer'

Example: "Dynamic Filter Visualizer"

Tunable: Yes

Position — Scope window position in pixels

[left bottom 800 500] (default) | four-element double vector

Scope window position in pixels, specified as a four-element double vector of the form [left bottom width height]. The default value of this property is dependent on the screen resolution, and is such that the window is positioned in the center of the screen, with a width and height of 800 and 500 pixels, respectively.

Tunable: Yes

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

MaximizeAxes — Maximize axes control

"Auto" (default) | "On" | "Off"

Specify whether to display the filter visualizer in maximized-axes mode. In this mode, the axes are expanded to fit into the entire display. To conserve space, labels do not appear in each display. Instead, tick-mark values appear on top of the plotted data. You can select one of the following options:

• "Auto" — The axes appear maximized in all displays only if the Title and YLabel properties are empty for every display. If you enter any value in any display for either of these properties, the axes are not maximized.

• "On" — The axes appear maximized in all displays. Any values entered into the Title and YLabel properties are hidden.

• "Off" — None of the axes appear maximized.

Tunable: Yes

Scope Window Use

Hover over the Dynamic Filter Visualizer window to see the maximize axes button .

Data Types: char | string

Title — Display title

'' (default) | character vector | string scalar

Display title, specified as a character vector or a string scalar.

Example: 'Magnitude Response'

Example: "Magnitude Response"

Tunable: Yes

Scope Window Use

In the Configuration section on the Plot tab of the Dynamic Filter Visualizer toolstrip, click Settings. In the Filter Visualizer Settings window that opens, under Display and Labels, set Title to a character vector or a string scalar.

YLimits — y-axis limits

[-25 25] (default) | two-element row vector

Y-axis limits, specified as a two-element numeric row vector with the second element greater than the first element and of the form [ymin, ymax].

Tunable: Yes

Scope Window Use

In the Configuration section on the Plot tab of the Dynamic Filter Visualizer toolstrip, click Settings. In the Filter Visualizer Settings window that opens, under Data and Axes, set Y-Axis Limits to a two-element numeric vector.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

ShowLegend — Show or hide legend

false (default) | true

When this property is set to false, no legend is displayed. When this property is set to true, a legend with automatic string labels for each input filter is displayed.

Tunable: Yes

Scope Window Use

In the Configuration section on the Plot tab of the Dynamic Filter Visualizer toolstrip, click Legend.

Data Types: logical

FilterNames — Names for input filters

{''} (default) | cell array of character vectors | array of strings

Names to label the input filters in the legend, specified as a cell array of character vectors or an array of strings. The default is an empty cell array. When this property is set to an empty cell array, the filters are named by default names, such as Filter 1, Filter 2, and so on.

Tunable: Yes

Scope Window Use

In the Configuration section on the Plot tab of the Dynamic Filter Visualizer toolstrip, click Legend. In the legend that appears on the plot, click the filter name.

ShowGrid — Display grid

true (default) | false

Set this property to true to show grid lines on the plot.

Scope Window Use

In the Configuration section on the Plot tab of the Dynamic Filter Visualizer toolstrip, click Settings. In the Filter Visualizer Settings window that opens, under Data and Axes, select Grid.

UpperMask — Upper limit mask

Inf (default) | two-column matrix

Upper limit spectral mask, specified as a two-column matrix. The first column represents the frequency values (Hz), and the second column represents the magnitude spectrum of the upper limit mask.

Tunable: Yes

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

LowerMask — Lower limit mask

-Inf (default) | two-column matrix

Lower limit spectral mask, specified as a two-column matrix. The first column represents the frequency values (Hz), and the second column represents the magnitude spectrum of the lower limit mask.

Tunable: Yes

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Usage

Syntax

dfv(filt)

dfv(B,A)

Description

dfv(filt) displays the time-varying magnitude response of the object filter, filt, in the Dynamic Filter Visualizer figure, as long as filt has a valid freqz() implementation.

dfv(B,A) displays the magnitude response for the digital filters with numerator and denominator polynomial coefficients stored in B1 and A1, B2 and A2, ..., and BN and AN, respectively.

Input Arguments

filt — Input filter

filter System object

Input filter System object with a valid freqz() implementation.

B — Numerator polynomial coefficients

row vector

Numerator polynomial coefficients, specified as a row vector.

Data Types: single | double

A — Denominator polynomial coefficients

scalar | row vector

Denominator polynomial coefficients, specified as a:

• scalar –– The filter is an FIR filter.

• row vector –– The filter is an IIR filter.

Data Types: single | double

Object Functions

Specific to dsp.DynamicFilterVisualizer

step	Display time-varying magnitude response
printToFigure	Print scope window to MATLAB figure

Specific to Scopes

show	Display scope window
hide	Hide scope window
isVisible	Determine visibility of scope
generateScript	Generate MATLAB script to create scope with current settings

Examples

Plot Time-Varying Magnitude and Phase Response of FIR Filter

Design an FIR filter with a time-varying magnitude and phase response. Plot this varying response on a dynamic filter visualizer in normalized frequency units.

Create a dsp.DynamicFilterVisualizer object. Set the PlotAsMagnitudePhase and the NormalizedFrequency properties to true.

dfv = dsp.DynamicFilterVisualizer(PlotAsMagnitudePhase=1,...
    NormalizedFrequency=true,ShowLegend=true,...
    Title='Magnitude and Phase Response',...
    FilterNames="FIR Filter")

dfv = 
  dsp.DynamicFilterVisualizer handle with properties:

               FFTLength: 2048
     NormalizedFrequency: 1
          FrequencyRange: [0 1]
                  XScale: 'Linear'
        MagnitudeDisplay: 'Magnitude (dB)'
    PlotAsMagnitudePhase: 1
                PlotType: 'Line'
             AxesScaling: 'Auto'

  Show all properties

Vary the cutoff frequency of the FIR filter k from 0.1 to 0.5 in increments of 0.001. View the varying magnitude and phase response using the dynamic filter visualizer.

for k = 0.1:0.001:0.5
    b = designLowpassFIR(FilterOrder=90,CutoffFrequency=k);
    dfv(b,1);
end

Plot Time-Varying Magnitude Response of Variable Bandwidth FIR Filter

Visualize the varying magnitude response of the variable bandwidth FIR filter using the dynamic filter visualizer.

Create a dsp.DynamicFilterVisualizer object.

dfv = dsp.DynamicFilterVisualizer(YLimits=[-160 10],...
    FilterNames="Variable Bandwidth FIR Filter")

dfv = 
  dsp.DynamicFilterVisualizer handle with properties:

               FFTLength: 2048
     NormalizedFrequency: 0
              SampleRate: 44100
          FrequencyRange: [0 22050]
                  XScale: 'Linear'
        MagnitudeDisplay: 'Magnitude (dB)'
    PlotAsMagnitudePhase: 0
                PlotType: 'Line'
             AxesScaling: 'Manual'

  Show all properties

Design a bandpass variable bandwidth FIR filter with a center frequency of 5 kHz and a bandwidth of 4 kHz.

Fs = 44100;
vbw = dsp.VariableBandwidthFIRFilter(FilterType='Bandpass',...
    FilterOrder=100,...
    SampleRate=Fs,...
    CenterFrequency=5e3,...
    Bandwidth=4e3);

Vary the center frequency of the filter. Visualize the varying magnitude response of the filter using the dsp.DynamicFilterVisualizer object.

for idx  = 1:100
    dfv(vbw);
    vbw.CenterFrequency = vbw.CenterFrequency + 20;
end

Print Dynamic Filter Visualizer Display to MATLAB Figure

Since R2023b

Use the printToFigure function to print the dsp.DynamicFilterVisualizer object display window to a new MATLAB® figure.

Create a dsp.DynamicFilterVisualizer object.

dfv = dsp.DynamicFilterVisualizer(YLimits=[-120 10]);

Design FIR filter with varying cutoff frequencies ranging from 0.1 to 0.5. Plot the magnitude response of the filter using the Dynamic Filter Visualizer.

for k = 0.1:0.001:0.5
    b = fir1(90, k);
    dfv(b,1);
end 

Print the display of the magnitude response to a new MATLAB figure. The function returns a handle to the figure.

scopeFig = printToFigure(dfv);

The handle to the figure scopeFig lets you modify the appearance and the behavior of the figure window.

Specify a figure name and change the size of the figure to 400-by-250 pixels.

scopeFig.Name="Magnitude Response of FIR Filter";
scopeFig.NumberTitle="off";
scopeFig.Position=[1 1 400 250];

When printing to figure, you can make the figure invisible by setting the Visible argument to false.

scopeFig = printToFigure(dfv,Visible=false);

Limitations

• Does not support C/C++ code generation using MATLAB^® Coder™. To generate a standalone application, use the MATLAB Compiler™.

• Supports MEX code generation by treating the calls to the object as extrinsic.

Version History

Introduced in R2018b

R2023b: Support for printToFigure function

You can print the dsp.DynamicFilterVisualizer object display window to a MATLAB figure using the new printToFigure function.

R2023a: Normalized frequency in dsp.DynamicFilterVisualizer

When you set the NormalizedFrequency property to true, the dynamic filter visualizer shows the frequency response of the filter in normalized frequency units (0 to 1).

R2022b: Filter names support array of strings

Starting in R2022b, you can specify the FilterNames property of the dsp.DynamicFilterVisualizer object as an array of strings.

dfv = dsp.DynamicFilterVisualizer(FilterNames=["Filter 1", "Filter 2"]);

R2022b: Enhancements to the dsp.DynamicFilterVisualizer object and the Dynamic Filter Visualizer UI

The dsp.DynamicFilterVisualizer object has the following new properties starting R2022b:

• PlotAsMagnitudePhase –– Split the magnitude and phase of the input signal and plot them on two separate axes within the same window

• PlotType –– Plot type

• AxesScaling –– Axes scaling mode

• AxesScalingNumUpdates –– Number of updates before scaling

• MaximizeAxes –– Maximize axes control

• ShowGrid –– Grid visibility

The Dynamic Filter Visualizer app that you launch using the object has these enhancements in R2022b:

• Magnitude Phase button –– This button corresponds to the PlotAsMagnitudePhase property in the object.

• Generate Script button –– Generate a script to re-create your dynamic filter visualizer plot with the same settings. When you click this button, an editor window opens with the code that you can use to re-create your dsp.DynamicFilterVisualizer object.

R2022b: Configure dsp.DynamicFilterVisualizer measurements programmatically

You can now configure the cursor and the peak finder measurements in the dsp.DynamicFilterVisualizer object programmatically using these properties:

• MeasurementChannel

• CursorMeasurements

• PeakFinder