Main Content

dsp.VariableBandwidthFIRFilter

Variable bandwidth FIR filter

Description

The dsp.VariableBandwidthFIRFilter object filters each channel of the input using FIR filter implementations. It does so while having the capability of tuning the bandwidth.

To filter each channel of the input:

  1. Create the dsp.VariableBandwidthFIRFilter object and set its properties.

  2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?

This object supports C/C++ code generation and SIMD code generation under certain conditions. For more information, see Code Generation.

Creation

Description

vbw = dsp.VariableBandwidthFIRFilter returns a variable bandwidth FIR filter object which independently filters each channel of the input over successive calls to the object. The filter cutoff frequency can be tuned during the filtering operation. The variable bandwidth FIR filter is designed using the window method.

example

vbw = dsp.VariableBandwidthFIRFilter(Name=Value) returns a variable bandwidth FIR filter with additional properties specified by one or more Name-Value pair arguments. Name is the property name and Value is the corresponding value. For example, FilterOrder=50 sets the filter order to 50.

Properties

expand all

Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

FIR filter order, specified as an even positive integer. This property is nontunable.

Data Types: double | single

Type of filter response, specified as one of these options:

  • 'Lowpass'

  • 'Highpass'

  • 'Bandpass'

  • 'Bandstop'

Filter cutoff frequency, specified as a real positive scalar in Hz or in normalized frequency units (since R2023a).

If you set the NormalizedFrequency property to:

  • false –– The value of the cutoff frequency is in Hz. The value must be less than half the SampleRate property value.

  • true –– The value of the cutoff frequency is in normalized frequency units. The value must be a positive scalar less than 1.0.

(since R2023a)

Tunable: Yes

Dependencies

To enable this property, set FilterType to 'Lowpass' or 'Highpass'.

Data Types: double | single

Window function used to design the FIR filter, specified as one of these options:

  • 'Hann'

  • 'Hamming'

  • 'Chebyshev'

  • 'Kaiser'

Kaiser window parameter, specified as a real scalar.

Dependencies

To enable this property, set the Window property to 'Kaiser'.

Data Types: double | single

Center frequency of filter, specified as a real positive scalar in Hz or in normalized frequency units (since R2023a).

If you set the NormalizedFrequency property to:

  • false –– The value of the center frequency is in Hz. The value must be less than half the SampleRate property value.

  • true –– The value of the center frequency is in normalized frequency units. The value must be a positive scalar less than 1.0.

(since R2023a)

Tunable: Yes

Dependencies

To enable this property, set the FilterType property to 'Bandpass' or 'Bandstop'.

Data Types: double | single

Filter bandwidth, specified as a real positive scalar in Hz or in normalized frequency units (since R2023a).

If you set the NormalizedFrequency property to:

  • false –– The value of the filter bandwidth is in Hz. The value must be less than half the SampleRate property value.

  • true –– The value of the filter bandwidth is in normalized frequency units. The value must be a positive scalar less than 1.0.

(since R2023a)

Tunable: Yes

Dependencies

To enable this property, set the FilterType property to 'Bandpass' or 'Bandstop'.

Data Types: double | single

Chebyshev window sidelobe attenuation, specified as a real positive scalar in dB.

Dependencies

To enable this property, set the Window property to 'Chebyshev'.

Data Types: double | single

Since R2023a

Flag to set frequencies in normalized units, specified as one of these values:

  • true –– The filter cutoff frequency, center frequency, and the filter bandwidth must be in the normalized frequency units and less than 1.0.

  • false –– The filter cutoff frequency, center frequency, and the filter bandwidth are in Hz. You can specify the input sample rate through the SampleRate property.

Data Types: logical

Input sample rate, specified as a positive scalar in Hz.

Dependency

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

Data Types: double | single

Usage

Description

example

y = vbw(x) filters the input signal x using the variable bandwidth FIR filter to produce the output y. The variable bandwidth FIR filter object operates on each channel, which means the object filters every column of the input signal independently over successive calls to the algorithm.

Input Arguments

expand all

Data input, specified as a vector or a matrix. This object also accepts variable-size inputs. Once the object is locked, you can change the size of each input channel, but you cannot change the number of channels.

Data Types: double | single
Complex Number Support: Yes

Output Arguments

expand all

Filtered output, returned as a vector or a matrix. The size, data type, and complexity of the output signal matches that of the input signal.

Data Types: double | single
Complex Number Support: Yes

Object Functions

To use an object function, specify the System object™ as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

expand all

freqzFrequency response of discrete-time filter System object
fvtoolVisualize frequency response of DSP filters
impzImpulse response of discrete-time filter System object
infoInformation about filter System object
coeffsReturns the filter System object coefficients in a structure
costEstimate cost of implementing filter System object
grpdelayGroup delay response of discrete-time filter System object
outputDelayDetermine output delay of single-rate or multirate filter
stepRun System object algorithm
releaseRelease resources and allow changes to System object property values and input characteristics
resetReset internal states of System object

Examples

collapse all

Tune the center frequency and the bandwidth of the FIR bandpass filter. Filter a sinusoidal signal through this filter.

Define a bandpass variable bandwidth FIR filter. Specify an input sample rate of 44100 Hz. Initialize a dsp.TransferFunctionEstimator object to estimate the transfer function of the filter from the input and output signals. To visualize the transfer function, initialize a dsp.ArrayPlot object.

Fs = 44100; 
vbw = dsp.VariableBandwidthFIRFilter(FilterType='Bandpass',...
    FilterOrder=100,...
    SampleRate=Fs,...
    CenterFrequency=1e4,...
    Bandwidth=4e3);
tfe = dsp.TransferFunctionEstimator(FrequencyRange='onesided');
aplot = dsp.ArrayPlot(PlotType='Line',...
    XOffset=0,...
    YLimits=[-120 5], ...
    SampleIncrement=44100/1024,...
    YLabel='Frequency Response (dB)',...
    XLabel='Frequency (Hz)',...
    Title='System Transfer Function');

Generate a sine wave signal with a frame length of 1024. Tune the bandwidth and the center frequency of the filter. Pass the signal through this filter. Estimate the transfer function of the filter using the input and the generated output. Plot the system transfer function using an array plot.

FrameLength = 1024;
sine = dsp.SineWave(SamplesPerFrame=FrameLength);
for i=1:500
    % Generate input
    x = sine() + randn(FrameLength,1);
    % Pass input through the filter
    y = vbw(x);
    % Transfer function estimation
    h = tfe(x,y);
    % Plot transfer function
    aplot(20*log10(abs(h)))
    % Tune bandwidth and center frequency of the FIR filter
    if (i==250)
        vbw.CenterFrequency = 5000;
        vbw.Bandwidth = 2000;
    end
end

Algorithms

expand all

References

[1] Jarske, P.,Y. Neuvo, and S. K. Mitra, "A simple approach to the design of linear phase FIR digital filters with variable characteristics." Signal Processing. Vol. 14, Issue 4, June 1988, pp. 313-326.

Extended Capabilities

Version History

Introduced in R2014a

expand all