Cast fixed-point filter to use double-precision arithmetic
hd = double(h)
hd = double(h) returns
a new filter hd that has the same structure and
coefficients as h, but whose arithmetic property
is set to double to use double-precision arithmetic
for filtering. double(h) is not the same as the reffilter(h) function:
hd, the filter returned by double has
the quantized coefficients of h represented in
double-precision floating-point format
The reference filter returned by reffilter has
double-precision, floating-point coefficients that have not been quantized.
You might find double(h) useful to isolate
the effects of quantizing the coefficients of a filter by using double to
create a filter hd that operates in double-precision
but uses the quantized filter coefficients.