Table Of Contents

Filter Design (Windowed FIR) (G Dataflow)

Version:
Last Modified: August 28, 2017

Designs a windowed FIR filter.

Programming Patterns

To filter a sequence of data, wire the filter output to the Filtering node.

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window parameter

A value that affects the output coefficients when window type is Kaiser, Gaussian, or Dolph-Chebyshev.

If window type is any other type of window, this node ignores this input.

This input represents the following information for each type of window:

  • Kaiser—Beta parameter
  • Gaussian—Standard deviation
  • Dolph-Chebyshev—The ratio of the main lobe to the side lobe, s, expressed in decibels

Default: NaN—Causes this node to set beta to 0 for a Kaiser window, the standard deviation to 0.2 for a Gaussian window, and s to 60 dB for a Dolph-Chebyshev window

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window type

Type of smoothing window. Smoothing windows decrease ripple in the filter passband and improve the ability of the filter to attenuate frequency components in the filter stopband.

Name Value Description
Rectangle 0 Specifies a rectangle window.
Hanning 1 Specifies a Hanning window.
Hamming 2 Specifies a Hamming window.
Blackman-Harris 3 Specifies a Blackman-Harris window.
Exact Blackman 4 Specifies an Exact Blackman window.
Blackman 5 Specifies a Blackman window.
Flat Top 6 Specifies a Flat Top window.
4 Term B-Harris 7 Specifies a 4 Term B-Harris window.
7 Term B-Harris 8 Specifies a 7 Term B-Harris window.
Low Sidelobe 9 Specifies a Low Sidelobe window.
Blackman Nuttall 11 Specifies a Blackman Nuttall window.
Triangle 30 Specifies a Triangle window.
Bartlett-Hanning 31 Specifies a Bartlett-Hanning window.
Bohman 32 Specifies a Bohman window.
Parzen 33 Specifies a Parzen window.
Welch 34 Specifies a Welch window.
Kaiser 60 Specifies a Kaiser window.
Dolph-Chebyshev 61 Specifies a Dolph-Chebyshev window.
Gaussian 62 Specifies a Gaussian window.

Default: 0—Rectangle

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option

An enum value that determines whether to scale the FIR windowed coefficients.

Name Description
not scaled

Does not scale the FIR windowed coefficients.

scaled

Scales the FIR windowed coefficients.

Default: not scaled

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filter type

The passband of the filter.

Name Description
Lowpass

Uses a lowpass filter.

Highpass

Uses a highpass filter.

Bandpass

Uses a bandpass filter.

Bandstop

Uses a bandstop filter.

Default: Lowpass

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low cutoff frequency

The low cutoff frequency in Hz. If this input is less than or equal to zero or does not meet the Nyquist criterion, the node returns an empty array as well as an error.

Default: 0.125

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high cutoff frequency

The high cutoff frequency, in Hz. This value must observe the Nyquist criterion.

The node places the following restrictions on this parameter according to filter type:

filter type Restrictions
Lowpass or Highpass The node ignores this input.
Bandpass or Bandstop This value must be greater than low cutoff frequency and less than half of sampling frequency.

Default: 0.45

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number of taps

The total number of FIR coefficients.

If number of taps is less than or equal to 0, the node returns an empty array as well as an error.

If filter type is 1 (Highpass) or 3(Bandstop), this input must be odd.

Default: 25

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error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

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sampling frequency

The sampling frequency in Hz.

If this input is less than or equal to 0, the node returns an empty array as well as an error.

Default: 1.0 Hz

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filter

Output FIR filter.

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filter structure

Structure of the output filter.

This output always returns FIR.

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forward coefficients

Coefficients of the FIR filter.

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reverse coefficients

This output always returns an empty array because FIR filters do not have reverse coefficients.

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sampling frequency

The sampling frequency in Hz.

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Where This Node Can Run:

Desktop OS: Windows

FPGA: This product does not support FPGA devices

Web Server: Not supported in VIs that run in a web application


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