dfilt.df2sos (Signal Processing Toolbox)

Construct a discrete-time, second-order section, direct form II filter object

Syntax

Hd = dfilt.df2sos(s)
Hd = dfilt.df2sos(b1,a1,b2,a2,...)
Hd = dfilt.df2sos(...,g)

Description

Hd = dfilt.df2sos(s) returns a discrete-time, second-order section, direct form II filter object, Hd, with coefficients given in the s matrix.

Hd = dfilt.df2sos(b1,a1,b2,a2,...) returns a discrete-time, second-order section, direct form II object, Hd, with coefficients for the first section given in the b1 and a1 vectors, for the second section given in the b2 and a2 vectors, etc.

Hd = dfilt.df2sos(...,g) includes a gain vector g. The elements of g are the gains for each section. The maximum length of g is the number of sections plus one. If g is not specified, all gains default to one.

Hd = dfilt.df2sos returns a default, discrete-time, second-order section, direct form II filter object, Hd. This filter passes the input through to the output unchanged.

Note If a(1) is not equal to 1, the 1/a(1) block is included as shown below. If a(1) is equal to 1, the 1/a(1) block is replaced by a direct connection.

Examples

Specify a second-order section, direct form II dfilt object for a Butterworth filter converted to second-order sections, with the following code:

[z,p,k] = butter(30,0.5);
[s,g] = zp2sos(z,p,k);
Hd = dfilt.df2sos(s,g)
Hd =
     FilterStructure: 'Direct form II, second-order-sections'
          sosMatrix: [15x6 double]
        ScaleValues: 2.5160e-008

dfilt.df2 dfilt.df2t