Interpolation FIR filter design

designs a linear phase FIR filter that performs ideal bandlimited interpolation using the
nearest `b`

= intfilt(`l`

,`p`

,`alpha`

)`2`

*`p`

nonzero samples, when used on a sequence
interleaved with `l`

-1 consecutive zeros every `l`

samples, assuming an original bandlimitedness of `alpha`

times the
Nyquist frequency. The returned filter `b`

is identical to that used by
`interp`

.

designs an FIR filter that performs `b`

= intfilt(`l`

,`n`

,`'Lagrange'`

)`n`

th-order Lagrange polynomial
interpolation on a sequence interleaved with `l`

-1 consecutive zeros
every `l`

samples.

The bandlimited method uses `firls`

to design an interpolation FIR filter. The
polynomial method uses Lagrange's polynomial interpolation formula on equally spaced samples
to construct the appropriate filter. Both types of filters are basically lowpass and have a
gain of `l`

in the passband.

`decimate`

| `downsample`

| `interp`

| `resample`

| `upsample`