Implement cascade of fourth-order section filter

The `dsp.FourthOrderSectionFilter`

implements a cascade of fourth
order section filters.

returns a
`fos`

= dsp.FourthOrderSectionFilter`FourthOrderSectionFilter`

object, `fos`

, that
implements a cascade of fourth order filter sections.

returns a `fos`

= dsp.FourthOrderSectionFilter(`num`

,`den`

)`FourthOrderSectionFilter`

object with the
`Numerator`

property set to `num`

and the
`Denominator`

property set to `den`

.

returns a `fos`

= dsp.FourthOrderSectionFilter(`Name,Value`

)`FourthOrderSectionFilter`

object with each specified property
name set to the specified value. You can specify additional name-value pair arguments in
any order.

```
fos =
dsp.FourthOrderSectionFilter('Numerator',num,'Denominator',den)
```