Design halfband filter
The Halfband Filter block has been removed from
the DSP System Toolbox™ block library. Existing instances of the Halfband
Filter block will continue to operate. To model FIR halfband
decimators and interpolators, use the FIR Halfband
Decimator and FIR Halfband Interpolator blocks.
These blocks replace the functionality of the Halfband Filter block,
when Impulse response is set to
Filtering / Filter Designs
This block brings the filter design capabilities of the
to the Simulink® environment.
See Halfband Filter Design Dialog Box — Main Pane for more information about the parameters of this block. The Data Types and Code Generation panes are not available for blocks in the DSP System Toolbox Filter Designs library.
This button opens the Filter Visualization Tool (
fvtool) from the Signal Processing Toolbox™ product.
You can use the tool to display:
Magnitude response, phase response, and group delay in the frequency domain.
Impulse response and step response in the time domain.
The tool also helps you evaluate filter performance by providing information about filter order, stability, and phase linearity. For more information on FVTool, see the Signal Processing Toolbox documentation.
In this group, you specify your filter type and order.
the drop-down list.
FIR is the default.
When you choose an impulse response, the design methods and structures
you can use to implement your filter change accordingly.
Note: The design methods and structures for FIR filters are not the same as the methods and structures for IIR filters.
Minimum (the default)
Specify from the drop-down list. Selecting
the Order option (see the following sections)
so you can enter the filter order.
Specify the filter response as
Interpolator. By default, the block
specifies a single-rate filter.
Enter the filter order. This option is enabled only when the Filter
order mode is set to
The parameters in this group allow you to specify your filter response curve. Graphically, the filter specifications for a halfband lowpass filter look similar to those shown in the following figure.
In the figure, the transition region lies between the end of the passband and the start of the stopband. The width is defined explicitly by the value of Transition width.
When Order mode is
set this parameter to
Use this parameter to specify whether your frequency settings
are normalized or in absolute frequency. Select
(0–1) to enter frequencies in normalized form.
This behavior is the default. To enter frequencies in absolute values,
select one of the frequency units from the drop-down list—
GHz. Selecting one of the unit options
enables the Input Fs parameter.
Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter input. When you provide an input sampling frequency, all frequencies in the specifications are in the selected units as well. This parameter is available when you select one of the frequency options from the Frequency units list.
Specify the width of the transition between the end of the passband and the edge of the stopband. Specify the value in normalized frequency units or the absolute units you select in Frequency units.
Parameters in this group specify the filter response in the passbands and stopbands.
Unconstrained (the default),
Stopband attenuation to constrain
the response in the stopband explicitly.
Specify the units for any parameter you provide in magnitude specifications. From the drop-down list, select one of the following options:
Linear — Specify
the magnitude in linear units.
dB — Specify the
magnitude in decibels (default).
When Magnitude units is
attenuation, enter the filter attenuation in the stopband
in the units you choose for Magnitude units,
either linear or decibels.
The parameters in this group allow you to specify the design method and structure of your filter.
Lists the design methods available for the frequency and magnitude
specifications you entered. For FIR halfband filters, the available
design options are
window. For IIR halfband filters, the available design
IIR quasi-linear phase.
The following design options are available for FIR halfband filters when the user specifies an equiripple design:
Select the checkbox to specify a minimum-phase design.
Stopband shape lets you specify how the stopband changes with increasing frequency. Choose one of the following options:
Flat — Specifies
that the stopband is flat. The attenuation does not change as the
Linear — Specifies
that the stopband attenuation changes linearly as the frequency increases.
Change the slope of the stopband by setting Stopband decay.
1/f — Specifies
that the stopband attenuation changes exponentially as the frequency
f is the frequency. Set the power
(exponent) for the decay in Stopband decay.
When you set Stopband shape, Stopband decay specifies the amount of decay applied to the stopband. the following conditions apply to Stopband decay based on the value of Stopband Shape:
When you set Stopband shape to
decay has no affect on the stopband.
When you set Stopband shape to
enter the slope of the stopband in units of dB/rad/s. The block applies
that slope to the stopband.
When you set Stopband shape to
enter a value for the exponent n in the relation
(1/f)n to define the stopband decay. The
block applies the (1/f)n relation to the
stopband to result in an exponentially decreasing stopband attenuation.
For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter.
Select this check box to implement the filter as a subsystem of basic Simulink blocks. Clear the check box to implement the filter as a high-level subsystem. By default, this check box is cleared.
The high-level implementation provides better compatibility across various filter structures, especially filters that would contain algebraic loops when constructed using basic elements. On the other hand, using basic elements enables the following optimization parameters:
Optimize for zero gains — Terminate chains that contain Gain blocks with a gain of zero.
Optimize for unit gains — Remove Gain blocks that scale by a factor of one.
Optimize for delay chains — Substitute delay chains made up of n unit delays with a single delay by n.
Optimize for negative gains — Use subtraction in Sum blocks instead of negative gains in Gain blocks.
Select this check box to scale unit gains between sections in SOS filters. This parameter is available only for SOS filters.
Specify how the block should process the input. The available options may vary depending on he settings of the Filter Structure and Use basic elements for filter customization parameters. You can set this parameter to one of the following options:
Columns as channels (frame based) —
When you select this option, the block treats each column of the input
as a separate channel.
Elements as channels (sample based) —
When you select this option, the block treats each element of the
input as a separate channel.
When the Filter type parameter specifies a multirate filter, select the rate processing rule for the block from following options:
Enforce single-rate processing —
When you select this option, the block maintains the sample rate of
Allow multirate processing —
When you select this option, the block adjusts the rate at the output
to accommodate an increased or reduced number of samples. To select
this option, you must set the Input processing parameter
Elements as channels (sample based).
Select this check box to enable the specification of coefficients using MATLAB® variables. The available coefficient names differ depending on the filter structure. Using symbolic names allows tuning of filter coefficients in generated code. By default, this check box is cleared.
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