Design inverse sinc filter
Filtering / Filter Designs
dspfdesign
This block brings the filter design capabilities of the filterbuilder
function to the Simulink^{®} environment.
See Inverse Sinc Filter Design — 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.
Polezero information.
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 format, such as the impulse response and the filter order.
Select either Minimum
(the default) or
Specify
from the dropdown list.
Selecting Specify
enables the
Order option (see the following sections)
so you can enter the filter order.
Select Lowpass
or
Highpass
to design an inverse sinc
lowpass or highpass filter.
Select Singlerate
,
Decimator
,
Interpolator
, or
Samplerate converter
. Your choice
determines the type of filter as well as the design methods and
structures that are available to implement your filter. By default,
the block specifies a singlerate filter.
Selecting Decimator
or
Interpolator
activates
the Decimation Factor or the
Interpolation Factor options
respectively.
Selecting Samplerate
converter
activates both
factors.
Enter the filter order. This option is enabled only if you set the
Order mode to
Specify
.
Enter the decimation factor. This option is enabled only if the
Filter type is set to
Decimator
or Samplerate
converter
. The default value is 2.
Enter the interpolation factor. This option is enabled only if the
Filter type is set to
Interpolator
or
Samplerate converter
. The default
value is 2.
The parameters in this group allow you to specify your filter response curve.
Regions between specification values such as Passband frequency and Stopband frequency represent transition regions where the filter response is not constrained.
When Order mode is
Specify
, select the filter features that
the block uses to define the frequency response characteristics. The
list contains the following options, when available for the filter
specifications.
Passband and stopband frequencies
— Define the filter by specifying the frequencies for
the edges for the stop and passbands.
Passband frequency
— For IIR
filters, define the filter by specifying frequencies for the
edges of the passband.
Stopband frequency
— For IIR
filters, define the filter by specifying frequencies for the
edges of the stopbands.
Cutoff (6dB) frequency
— For FIR
filters, define the filter response by specifying the
locations of the 6 dB point. The 6 dB point is the frequency
for the point six decibels below the passband value.
Use this parameter to specify whether your frequency settings are
normalized or in absolute frequency. Select Normalized (0
to 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 dropdown
list—Hz
,
kHz
, MHz
, or
GHz
. Selecting one of the unit options
enables the Input sample rate 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.
Enter the frequency at the end of the passband. Specify the value in either normalized frequency units or the absolute units you select in Frequency units.
Enter the frequency at the start of the stopband. Specify the value in either normalized frequency units or the absolute units you select in Frequency units.
When Frequency constraints is Cutoff
(6dB) frequency
, specify the frequency of the 6 dB
point. Specify the value in either normalized frequency units or the
absolute units you select Frequency units.
Parameters in this group specify the filter response in the passbands and stopbands.
Specify the units for any parameter you provide in magnitude specifications. From the dropdown list, select one of the following options:
Linear
— Specify the
magnitude in linear units.
dB
— Specify the
magnitude in decibels (default)
Squared
— Specify the
magnitude in squared units.
Enter the filter ripple allowed in the passband in the units you choose for Magnitude units, either linear or decibels.
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. When you change the specifications for a
filter, such as changing the impulse response, the methods available
to design filters changes as well. The default FIR method is
Equiripple
.
The options for each design are specific for each design method. This section does not present all of the available options for all designs and design methods. There are many more that you encounter as you select different design methods and filter specifications. The following options represent some of the most common ones available.
Density factor controls the density of the frequency grid over which the design method optimization evaluates your filter response function. The number of equally spaced points in the grid is the value you enter for Density factor times (filter order + 1).
Increasing the value creates a filter that more closely approximates an ideal equiripple filter but increases the time required to design the filter. The default value of 20 represents a reasonable trade between the accurate approximation to the ideal filter and the time to design the filter.
Specify the phase constraint of the filter as
Linear
,
Maximum
, or
Minimum
.
When you select this parameter, the design method
determines and design the minimum order filter to meet
your specifications. Some filters do not provide this
parameter. Select Any
,
Even
, or
Odd
from the dropdown
list to direct the design to be any minimum order, or
minimum even order, or minimum odd order.
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 frequency
increases.
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 increases, where
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 Flat
,
Stopband decay has no affect
on the stopband.
When you set Stopband
shape to Linear
,
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 1/f
, 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.
A frequency dilation factor. The Sinc frequency factor, C , parameterizes the passband magnitude response for a lowpass design through H(ω) = sinc(Cω)^(P) and through H(ω) = sinc(C(1ω))^(P) for a highpass design.
Negative power of passband magnitude response. The Sinc power, P, parameterizes the passband magnitude response for a lowpass design through H(ω) = sinc(Cω)^(P) and through H(ω) = sinc(C(1ω))^(P) for a highpass design.
For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter. By default, FIR filters use directform structure, and IIR filters use directform II filters with SOS.
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 highlevel subsystem. By default, this check box is cleared.
The highlevel 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.
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 singlerate processing
— When you select this option, the block maintains the
sample rate of the input.
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 to 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.
Port  Supported Data Types 

Input 

Output 
