WindowedFirBandstopFilter Class

Measurement Studio 2019 Help

Edition Date: May 2019

Part Number: 375857B-01

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Note: This topic applies to the following Measurement Studio editions: Enterprise, Professional.

Implements a windowed FIR bandstop filter using the specified window type.

Namespace: NationalInstruments.Analysis.Dsp.Filters

Assembly: NationalInstruments.Analysis.Enterprise (in NationalInstruments.Analysis.Enterprise.dll) Version: 19.0.45.49153 (19.0.45.49153)

Syntax

Visual Basic (Declaration)
Public Class WindowedFirBandstopFilter _
	Inherits FirFilterBase

C#
public class WindowedFirBandstopFilter : FirFilterBase

Remarks

Smoothing windows decrease ripple in the filter passband and improve the ability of the filter to attenuate frequency components in the filter stopband. To design a FIR filter by windowing, you start with an ideal frequency response, calculate its impulse response, and then truncate the impulse response to produce a finite number of coefficients. To meet the linear-phase constraint, maintain symmetry about the center point of the coefficients. The truncation of the ideal impulse response results in the effect known as the Gibbs phenomenon. The Gibbs phenomenon is oscillatory behavior near abrupt transitions, or cutoff frequencies, in the FIR filter frequency response.

You can reduce the effects of the Gibbs phenomenon by using a smoothing window function to smooth the truncation of the ideal impulse response. By tapering the FIR coefficients at each end, you can diminish the height of the side lobes in the frequency response. However, the disadvantage to this method is that the main lobe widens, resulting in a wider transition region at the cutoff frequencies. The selection of a window function is similar to the choice between Chebyshev and Butterworth IIR filters. It is a trade-off between side lobe levels near the cutoff frequencies and width of the transition region.

Designing FIR filters by windowing is computationally inexpensive. Therefore, it is the fastest way to design FIR filters. However, it is not necessarily the best FIR filter design method.

Inheritance Hierarchy

System.Object
  NationalInstruments.Analysis.Dsp.Filters.FirFilterBase
    NationalInstruments.Analysis.Dsp.Filters.WindowedFirBandstopFilter

Thread Safety

Any public static (Shared in Visual Basic) members of this type are safe for multithreaded operations. Any instance members are not guaranteed to be thread safe.

See Also

Reference

WindowedFirBandstopFilter Members

NationalInstruments.Analysis.Dsp.Filters Namespace

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