Modify frequency content of `timeseries`

objects

`tsout = filter(`

applies the rational
transfer function filter `tsin`

,`b`

,`a`

)*b*(*z*^{−1})/*a*(*z*^{−1}) to the uniformly-spaced data in the `timeseries`

object `tsin`

. The numerator `b`

and denominator
`a`

are vectors containing the transfer function
coefficients.