Discrete-time, second-order section, direct-form II transposed filter
Hd = dfilt.df2tsos(b1,a1,b2,a2,...) returns a discrete-time, second-order section, direct-form II, tranposed filter, 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.df2tsos(...,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.
The resulting filter states column vector is
Specify a second-order sections, direct-form II, transposed discrete-time filter with coefficients from a sixth order, lowpass, elliptical filter using the following code:
[z,p,k] = ellip(6,1,60,.4); % Obtain filter coefficients [s,g] = zp2sos(z,p,k); % Convert to SOS Hd = dfilt.df2tsos(s,g)