Discrete-time, lattice allpass filter
hd = dfilt.latticeallpass(k)
hd = dfilt.latticeallpass
hd = dfilt.latticeallpass(k) returns
a discrete-time, lattice allpass filter object
with lattice coefficients,
Make this filter a fixed-point or single-precision filter by
changing the value of the
for the filter
hd as follows:
To change to single-precision filtering, enter
To change to fixed-point filtering, enter
hd = dfilt.latticeallpass returns
a default, discrete-time, lattice allpass filter object
k=[ ]. This filter passes the input through
to the output unchanged.
The following figure shows the signal flow for the allpass lattice
filter implemented by
help you see how the filter processes the coefficients, input, and
states of the filter, as well as numerical operations, the figure
includes the locations of the formatting objects within the signal
To help you understand where and how the filter performs fixed-point arithmetic during filtering, the figure shows various labels associated with data and functional elements in the filter. The following table describes each label in the signal flow and relates the label to the filter properties that are associated with it.
The labels use a common format — a prefix followed by the word “format.” In this use, “format” means the word length and fraction length associated with the filter part referred to by the prefix.
For example, the InputFormat label refers to the word length
and fraction length used to interpret the data input to the filter.
The format properties
shown in the table) store the word length and the fraction length
in bits. Or consider NumFormat, which refers to the word and fraction
associated with representing filter numerator coefficients.
Signal Flow Label
Corresponding Word Length Property
Corresponding Fraction Length Property
Most important is the label position in the diagram, which identifies where the format applies.
As one example, look at the label ProductFormat, which always
follows a coefficient multiplication element in the signal flow. The
label indicates that coefficients leave the multiplication element
with the word length and fraction length associated with product operations
that include coefficients. From reviewing the table, you see that
the ProductFormat refers to the properties
ProductMode that fully define the coefficient
format after multiply (or product) operations.
In this table you see the properties associated with the allpass
lattice implementation of
The table lists all the properties that a filter can have. Many of the properties are dynamic, meaning they exist only in response to the settings of other properties. You might not see all of the listed properties all the time. To view all the properties for a filter at any time, use
hd is a filter.
Specifies the fraction length used to interpret data
output by the accumulator. This is a property of FIR filters and lattice
filters. IIR filters have two similar properties —
Determines how the accumulator outputs stored values.
Choose from full precision (
Sets the word length used to store data in the accumulator/buffer.
Defines the arithmetic the filter uses. Gives you the
Specifies whether to cast numeric data to the appropriate accumulator format (as shown in the signal flow diagrams) before performing sum operations.
Specifies whether the filter automatically chooses the
proper fraction length to represent filter coefficients without overflowing.
Turning this off by setting the value to
Specifies the word length to apply to filter coefficients.
Describes the signal flow for the filter object, including all of the active elements that perform operations during filtering — gains, delays, sums, products, and input/output.
Specifies the fraction length the filter uses to interpret input data.
Specifies the word length applied to interpret input data.
Any lattice structure coefficients. No default value.
Sets the fraction length applied to the lattice coefficients.
Determines how the filter interprets the filter output
data. You can change the value of
Sets the mode the filter uses to scale the filtered data for output. You have the following choices:
Determines the word length used for the output data.
Sets the mode used to respond to overflow conditions
in fixed-point arithmetic. Choose from either
For the output from a product operation, this sets the
fraction length used to interpret the data. This property becomes
writable (you can change the value) when you set
Determines how the filter handles the output of product
operations. Choose from full precision (
Specifies the word length to use for multiplication operation
results. This property becomes writable (you can change the value)
when you set
Specifies whether to reset the filter states and memory
before each filtering operation. Lets you decide whether your filter
retains states from previous filtering runs.
Sets the mode the filter uses to quantize numeric values when the values lie between representable values for the data format (word and fraction lengths).
The choice you make affects only the accumulator and output arithmetic. Coefficient and input arithmetic always round. Finally, products never overflow — they maintain full precision.
Specifies whether the filter uses signed or unsigned fixed-point coefficients. Only coefficients reflect this property setting.
When you set
This property contains the filter states before, during,
and after filter operations. States act as filter memory between filtering
runs or sessions. The states use
Sets the word length used to represent the filter states.
Specify a third-order lattice allpass filter structure for a
with the following code:
k = [.66 .7 .44]; hd=dfilt.latticeallpass(k); % convert to fixed-point arithmetic hd.arithmetic = 'fixed';