Discrete-time, second-order section, direct-form II transposed filter
Hd = dfilt.df2tsos(s)
Hd = dfilt.df2tsos(b1,a1,b2,a2,...)
Hd = dfilt.df2tsos(...,g)
Hd = dfilt.df2tsos
Hd = dfilt.df2tsos(b1,a1,b2,a2,...) returns a discrete-time, second-order section, direct-form II, transposed 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
Design a second-order sections, direct-form II, transposed discrete-time filter starting from a 6th-order lowpass elliptic filter. Specify a passband edge frequency of rad/sample, a passband ripple of 1 dB, and a stopband attenuation of 60 dB. Visualize the filter response.
[z,p,k] = ellip(6,1,60,0.4); % Obtain filter coefficients [s,g] = zp2sos(z,p,k); % Convert to SOS Hd = dfilt.df2tsos(s,g); fvtool(Hd)