When the desired interpolation factor, L, can be expressed as a product of I positive integer factors, as
L = L1L1 ... LI
the desired interpolation can be realized as a cascade of I interpolators, each interpolating by one of the factors, Li. Compared to a single-stage interpolator design, a design that adopts a multistage approach usually results in a reduced total computational burden, reduced memory usage, simpler filter designs, and reduced sensitivity to finite word-length effects in the implementation of the filters.
In lowpass FIR filter designs, the number of required taps, N, is approximately inversely proportional to the normalized transition bandwidth:
where fp is the passband edge fequency ...