d=fdesign.fracdelay(.30)
 
d =
 
               Response: 'Fractional Delay'
          Specification: 'N'               
            Description: {'Filter Order'}  
              FracDelay: 0.3               
    NormalizedFrequency: true              
            FilterOrder: 3                 
                                           
designmethods(d)

Design Methods for class fdesign.fracdelay (N):

lagrange

help(d,'lagrange')

DESIGN Design a Lagrange fractional delay filter.
HD = DESIGN(D, 'lagrange') designs a Lagrange filter specified by the
  FDESIGN object D, and returns the DFILT object HD.
 
HD = DESIGN(..., 'FilterStructure', STRUCTURE) returns a filter with the
 structure STRUCTURE.  STRUCTURE is 'farrowfd' by default and can be any of
 the following:

'farrowfd'
'fd'
 
 % Example #1 - Design a linear Lagrange fractional delay filter of 0.2 samples.
 h = fdesign.fracdelay(0.2,'N',2);
 Hd = design(h, 'lagrange', 'FilterStructure', 'farrowfd')
 
 % Example #2 - Design a cubic Lagrange fractional delay filter
 Fs = 8000;      % Sampling frequency of 8kHz
 fdelay = 50e-6; % Fractional delay of 50 microseconds.
 h  = fdesign.fracdelay(fdelay,'N',3,Fs);
 Hd = design(h, 'lagrange', 'FilterStructure', 'farrowfd');

h = fdesign.fracdelay(0.2,'N',2); 
hd = design(h,'lagrange','FilterStructure','farrowfd')

Fs = 8000;      % Sampling frequency of 8 kHz.
fdelay = 50e-6; % Fractional delay of 50 microseconds.
h  = fdesign.fracdelay(fdelay,'N',3,Fs);
hd = design(h,'lagrange','FilterStructure','farrowfd');