Singlesection or multiplesection allpass filter
DSP System Toolbox / Filtering / Filter Implementations
The Allpass Filter block filters each channel of the input signal independently using a singlesection or multiplesection (cascaded) allpass filter. You can implement the allpass filter using a minimum multiplier, wave digital filter, or a lattice structure.
In minimum multiplier form, the block uses the minimum number of required multipliers, n, with 2n delay units and 2n adders. In wave digital filter form, the block uses only n multipliers and n delay units, at the expense of 3n adders. The lattice structure uses 2n multipliers, n delay units, and 2n adders. For more details on these structures, see Algorithms.
Data Types 

Multidimensional Signals 

VariableSize Signals 

[1] Regalia, Philip A., Sanjit K. Mitra, and P.P.Vaidyanathan. “The Digital AllPass Filter: A Versatile Signal Processing Building Block.” Proceedings of the IEEE. 76, no. 1 (1988): 19–37.
[2] Lutovac, M., D. Tosic, and B. Evans. Filter Design for Signal Processing Using MATLAB and Mathematica. Upper Saddle River, NJ: Prentice Hall, 2001.