L=filterbanklength(Ls,a);
filterbanklength(Ls,a) returns the length of a filterbank with time shifts a, such that it is long enough to expand a signal of length Ls.
If the filterbank length is longer than the signal length, the signal will be zero-padded by filterbank or ufilterbank.
If instead a set of coefficients are given, call filterbanklengthcoef.