Re: Designing a first-order IIR filter

[Shaun Jackman]

On 11/6/06, Doug Stewart <address@hidden> wrote:
> >> octave-forge has butter, cheby1, cheby2 and ellip
> >> for designing IIR filters.
> >>
> >
> > Thank you. These are all very good suggestions.
> >
> > I am particularly interested in designing a first-order filter. I
> > believe the above filters are exclusively higher-order -- please
> > correct me if I'm wrong. Or can one (all?) of the above be used to
> > design a first-order filter?
> >
> Just give it a try. It works.
> Doug

Thanks! It does mostly work. The only caveat being that a first-order
Butterworth filter gave two taps in the numerator:

octave:1> [b, a] = butter(1, 0.01)
b =

 0.015466  0.015466

a =

  1.00000  -0.96907

I simply moved the weight from the second tap to the first tap:

octave:2> b = [b(1) + b(2) 0]
b =

 0.030933  0.000000

Thanks for the help!
Shaun