dfilt.dfsymfir (Signal Processing Toolbox)

Construct a discrete-time, direct form symmetric FIR filter object

Syntax

Hd = dfilt.dfsymfir(b)
Hd = dfilt.dfsymfir

Description

Hd = dfilt.dfsymfir(b) returns a discrete-time, direct form symmetric FIR filter object, Hd, with numerator coefficients b.

Hd = dfilt.dfsymfir returns a default, discrete-time, direct form symmetric FIR filter object, Hd, with b=1. This filter passes the input through to the output unchanged.

Note Only the first half of vector b is used because the second half is assumed to be symmetric. In the figure below for an odd number of coefficients, b(3) = 0, b(4) = b(2) and b(5) = b(1), and in the next figure for an even number of coefficients, b(4) = b(3), b(5) = b(2), and b(6) = b(1).

Examples

Odd Order

Specify a fifth-order direct form symmetric FIR filter structure for a dfilt object, Hd, with the following code:

b = [-0.008 0.06 0.44 0.44 0.06 -0.008];
Hd = dfilt.dfsymfir(b);
Hd =
     FilterStructure: 'Direct form symmetric FIR'
           Numerator: [1x6 double]

get(Hd,'numerator')
ans =
   -0.0080    0.0600    0.4400    0.4400    0.0600   -0.0080

Even Order

Specify a fourth-order direct form symmetric FIR filter structure for a dfilt object, Hd, with the following code:

b = [-0.01 0.1 0.8 0.1 -0.01];
Hd = dfilt.dfsymfir(b)
Hd =
     FilterStructure: 'Direct form symmetric FIR'
           Numerator: [-0.0100 0.1000 0.8000 0.1000 -0.0100]

dfilt.dffirt dfilt.latticeallpass