[music-dsp] Vectorising IIR Filters

[Remy Muller]

These 2 articles discuss Block Recursion and ARMA filter unrolling in depth:

Burrus, C. S. (1971, November). Block Implementation of Digital Filters. 
IEEE Transactions on Circuit Theory, CT-18(6), 697–701.
Burrus, C. S. (1972, October). Block Realization of Digital Filters. 
IEEE Transactions on Audio and Electroacoustics, AU-20(4), 230–235.

you can also find some explanation in the Block Recursion section of 
this page:
http://cnx.org/content/m16339/latest/

Unfortunately as others have mentionned this also increase the 
complexity of the filter.