dsp.DynamicFilterVisualizer

Display time-varying magnitude response of digital filters

Description

The dsp.DynamicFilterVisualizer object displays the magnitude 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™.

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

FFTLength — FFT length

2048 (default) | positive integer

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

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

SampleRate — Sampling rate of input

44100 (default) | positive scalar

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

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

FrequencyRange — Range of frequency axis

[20 20e3] (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]. The upper limit must be less than or equal to Fs/2, where Fs is the value specified in SampleRate.

Tunable: Yes

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

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

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

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

YLimits — y-axis limits

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

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

Tunable: Yes

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

Data Types: logical

FilterNames — Names for input filters

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

Set this property to a cell array of character vectors to label the input filters in the legend. 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

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.

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.

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

Position — Scope window position in pixels

[880 495 800 450] (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 410 and 300 pixels, respectively.

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

Specific to Scopes

show	Display scope window
hide	Hide scope window

Examples

Plot Time-Varying Magnitude Response of FIR Filter

Design an FIR filter with time-varying magnitude response. Plot this varying response on a dynamic filter visualizer.

Create a dsp.DynamicFilterVisualizer object.

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

dfv = 
  DynamicFilterVisualizer with properties:

           FFTLength: 2048
          SampleRate: 44100
      FrequencyRange: [0 22050]
              XScale: 'Linear'
    MagnitudeDisplay: 'Magnitude (dB)'

   Visualization
                Name: 'Dynamic Filter Visualizer'
               Title: 'Magnitude Response'
             YLimits: [-120 10]
          ShowLegend: 0
         FilterNames: {''}
           UpperMask: Inf
           LowerMask: -Inf
            Position: [880 495 800 450]

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

for k = 0.1:0.001:0.5
    b = fir1(90,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 dyamic filter visualizer.

Create a dsp.DynamicFilterVisualizer object.

dfv = dsp.DynamicFilterVisualizer('YLimits',[-160 10])

dfv = 
  DynamicFilterVisualizer with properties:

           FFTLength: 2048
          SampleRate: 44100
      FrequencyRange: [0 22050]
              XScale: 'Linear'
    MagnitudeDisplay: 'Magnitude (dB)'

   Visualization
                Name: 'Dynamic Filter Visualizer'
               Title: 'Magnitude Response'
             YLimits: [-160 10]
          ShowLegend: 0
         FilterNames: {''}
           UpperMask: Inf
           LowerMask: -Inf
            Position: [880 495 800 450]

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