# FIR Narrowband Filter Design (G Dataflow)

Designs a digital interpolated FIR (IFIR) filter.

##### Programming Patterns

You can design narrowband FIR filters using the FIR Narrowband Filter Design node, and then implement the filtering using the FIR Narrowband Filtering node. The design and implementation are separate operations, because many narrowband filters require long design times, whereas the actual filtering is fast and efficient.

## filter type

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

## passband frequency

The passband bandwidth.

The value for this input must be greater than 0 and less than half of sampling frequency.

Default: 0.01

## stopband frequency

The stopband bandwidth.

The value for this input must be greater than 0 and less than half of sampling frequency.

Default: 0.02

## center frequency

The center frequency of the filter.

The value for this input must be greater than 0 and less than half of sampling frequency.

Default: 0.2

## 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

## sampling frequency

The sampling frequency in Hz. If sampling frequency is less than or equal to zero, this node returns an empty cluster for IFIR filter as well as an error.

Default: 1.0

## passband ripple

The ripple in the passband of the filter.

The value of this input must be greater than 0.

Default: 0.01

## stopband attenuation

The attenuation in the stopband of the filter.

The value of this input must be greater than 0.

Default: 60 decibels

## IFIR filter

The IFIR filter.

### filter type

Filter type of the IFIR filter.

Name Description
Lowpass

The IFIR filter is a lowpass filter.

Highpass

The IFIR filter is a highpass filter.

Bandpass

The IFIR filter is a bandpass filter.

Bandstop

The IFIR filter is a bandstop filter.

Wideband-Lowpass

The IFIR filter is a wideband-lowpass filter with cutoff frequencies near Nyquist.

Wideband-Highpass

The IFIR filter is a wideband-highpass filter with cutoff frequencies near zero.

### interpolation

The interpolation factor M.

The model filter in this is stretched by interpolation times.

### Model Filter

The coefficients of the model filter.

### Image Suppressor

The coefficients of the filter image suppressor.

## 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.

## Algorithm for Calculating the Delay for the Filter

The overall filter is a linear-phase FIR filter. This node calculates the delay for the filter using the following equation:

$\mathrm{delay}=\frac{\left[\left({N}_{G}-1\right)M+{N}_{I}\right]}{2}$

where

• NG is the number of elements in Model Filter
• NI is the number of elements in Image Suppressor
• M is the value of interpolation

Where This Node Can Run:

Desktop OS: Windows

FPGA: Not supported

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