visualize

Visualize frequency response of individual filter stages or sum of filter paths between input and output channels

Since R2024b

Syntax

visualize(filtObj)

visualize(filtObj,NFFT)

visualize(___,Name=Value)

DFV = visualize(___)

Description

visualize(filtObj) visualizes the frequency response of the individual filters of the input filter object.

visualize(filtObj,NFFT) uses NFFT bins to calculate the frequency response of the filter object.

visualize(___,Name=Value) visualizes the frequency response of the filter with additional properties specified by one or more name-value arguments.

For example, to visualize the frequency response of the sum of all filter paths between each input and output channel, set SumFilterPaths to true.

Example: visualize(filtobj,SumFilterPaths=true,NumInputChannels=2)

DFV = visualize(___) returns the handle to the dsp.DynamicFilterVisualizer object which contains the settings to customize the filter visualization.

Examples

Visualize Frequency Response of Filters

Use the visualize function to visualize the frequency response of the individual filters in a SIMO system and the sum of the filters between each input channel and output channel pair. The SIMO system models one input channel, two output channels, and two paths between each input channel and output channel pair.

Design four lowpass FIR filters with varying cutoff frequencies. The filter order for each filter is 400.

order = 4000;
num  = [ % Path 1, Output Channel 1
    designLowpassFIR(FilterOrder=order,CutoffFrequency=0.2);...
    % Path 2, Output Channel 1
    designLowpassFIR(FilterOrder=order,CutoffFrequency=0.3);...
    % Path 1, Output Channel 2
    designLowpassFIR(FilterOrder=order,CutoffFrequency=0.4);...
    % Path 2, Output Channel 2
    designLowpassFIR(FilterOrder=order,CutoffFrequency=0.5)];

Initialize the dsp.MIMOFIRFilter with the array of filters.

simoFilt = dsp.MIMOFIRFilter(num,NumPaths=2)

simoFilt = 
  dsp.MIMOFIRFilter with properties:

       NumeratorSource: 'Property'
             Numerator: [4x4001 double]
              NumPaths: 2
    SumFilteredOutputs: true

Visualize the frequency response of the four individual filters. Update the title of the filter visualizer using the Title property of the visualization handle.

vizHandle = visualize(simoFilt)

vizHandle = 
  dsp.DynamicFilterVisualizer handle with properties:

               FFTLength: 8192
     NormalizedFrequency: 1
          FrequencyRange: [0 1]
                  XScale: 'Linear'
        MagnitudeDisplay: 'Magnitude (dB)'
    PlotAsMagnitudePhase: 0
                PlotType: 'Line'
             AxesScaling: 'Auto'

  Show all properties

vizHandle.Title = "Magnitude Response of Individual Filters";

Visualize the frequency response of the sum of all the filters between each input channel and output channel by setting the SumFilterPaths to true.

To use the SumFilterPaths property, you must pass input data to the MIMO FIR filter object or set the NumInputChannels property of the visualize function to a positive integer. In this case, set NumInputChannels to 1.

vizHandle = visualize(simoFilt,NumInputChannels=1,SumFilterPaths=true);

Update the filter visualizer title accordingly.

vizHandle.Title = "Magnitude Response of Sum of Filter Paths";

Filter Input Signal Using 1-by-2 SIMO System

Design four bandpass FIR filters, each with a different center frequency, specified in normalized frequency units. The bandwidth for each filter is 0.1. The SIMO system models one input channel, two output channels, and two paths between each input channel and output channel pair.

bw = 0.1;
num = [ % Path 1, Output Channel 1
    designBandpassFIR(CenterFrequency=0.5,bandwidth=bw);...
    % Path 2, Output Channel 1
    designBandpassFIR(CenterFrequency=0.6,bandwidth=bw);...
    % Path 1, Output Channel 2
    designBandpassFIR(CenterFrequency=0.7,bandwidth=bw);...
    % Path 2, Output Channel 2
    designBandpassFIR(CenterFrequency=0.8,bandwidth=bw)];

Initialize the dsp.MIMOFIRFilter object with the array of filters. Set the number of filter paths to 2.

simoFilt = dsp.MIMOFIRFilter(num,NumPaths=2)

simoFilt = 
  dsp.MIMOFIRFilter with properties:

       NumeratorSource: 'Property'
             Numerator: [4x101 double]
              NumPaths: 2
    SumFilteredOutputs: true

Visualize the frequency response of the individual filter stages using the visualize function.

visualize(simoFilt)

The input contains two sinusoidal signals, each with a frame length of 256. The first sinusoidal signal has a frequency of 2100 Hz and the second sinusoidal signal has a frequency of 3000 Hz.

Fs   = 8000;
frameLen  = 256;
sin_2100Hz = dsp.SineWave(Frequency=2100,SampleRate=Fs,...
    SamplesPerFrame=frameLen);
sin_3kHz  = dsp.SineWave(Frequency=3e3,SampleRate=Fs,...
    SamplesPerFrame=frameLen);

Initialize a spectrumAnalyzer object to view the spectrum of the input and the filtered output.

specScope = spectrumAnalyzer(SampleRate=Fs,PlotAsTwoSidedSpectrum=false,...
    ChannelNames={'Input','Output Channel 1',...
    'Output Channel 2'},ShowLegend=true);

Stream in 1e4 frames of the noisy input sinusoidal signal. The input noise is white Gaussian with a mean of 0 and a variance of 0.01. Since there are four filters, one input channel, and two paths between each input channel and output channel, the number of output channels of the system is given by $\frac{4}{\left(1\times 2\right)}=2$. Pass the signal through the designed filter. Visualize the spectrum of the input and output signals in the spectrum analyzer.

for idx = 1:1e4
    x = sin_2100Hz() + sin_3kHz() + 0.01 * randn(frameLen, 1);
    y = simoFilt(x);
    specScope([x, y]);
end

Visualize the frequency response of sum of all the filter paths between each input channel and output channel by setting SumFilterPaths to true.

visualize(simoFilt,SumFilterPaths=true)

Input Arguments

filtObj — Input filter

dsp.FrequencyDomainFIRFilter | dsp.MIMOFIRFilter

Input filter, specified as one of these filter objects:

• dsp.FrequencyDomainFIRFilter

• dsp.MIMOFIRFilter

NFFT — Number of FFT bins

8192 (default) | positive integer

Number of FFT bins the function uses to calculate the frequency response, specified as a positive integer.

Data Types: single | double

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: vizHandle = visualize(filtObj,SumFilterPaths=true,NumInputChannels=2)

SumFilterPaths — Visualize sum of frequency response of all filter paths between input and output channel

false (default) | true

Visualize the sum of the frequency response of all filter paths between a given input and output channel, specified as one these:

• true –– The function visualizes the sum of the frequency response of all filter paths between a given input and output channel.

• false –– The function visualizes the frequency response of the individual filter stages.

Data Types: logical

NumInputChannels — Number of input channels

positive integer

Number of input channels, specified as a positive integer. When you set SumFilterPaths to true and do not specify any input data to the input filter object, the visualize function uses the value in this property to determine the number of input channels in the input.

Data Types: single | double

Output Arguments

DFV — Handle to dynamic filter visualizer object

dsp.DynamicFilterVisualizer object

Handle to the dynamic filter visualizer object, returned as a dsp.DynamicFilterVisualizer object. Using this handle, you can customize the display properties, measurements, and color and styling properties of the dynamic filter visualizer.

Version History

Introduced in R2024b