A general approach to variable filtering is to tabulate the filter
coefficients as a function of the desired variables. In the case of
fractional delay filters, the impulse response
is
tabulated as a function of delay
,
,
, where
is the
interpolation-filter order. For each
,
may be sampled
sufficiently densely so that linear interpolation will give a
sufficiently accurate ``interpolated table look-up'' of
for each
and (continuous)
. This method is commonly used
in closely related problem of sampling-rate conversion
[464].