Reply by Jon Harris April 8, 20042004-04-08
"Jerry Avins" <jya@ieee.org> wrote in message
news:4075aa41$0$1650$61fed72c@news.rcn.com...
> bngguy wrote: > > > hi! Jerry, > > am trying to derive a digital filter from its analog prototype... > > let me know if u have any leads.... > > > > thanks > > > > > > Jerry Avins <jya@ieee.org> wrote in message
news:<4074c6e9$0$1658$61fed72c@news.rcn.com>...
> > > >>bngguy wrote: > >> > >> > >>>does any body know how to determine the analog prototype of a bessel
filter???
> >>> > >>>thanks > >> > >>Eh? Do you mean, given a digital Bessel filter (there are few reasons to > >>want one), how can one determine the analog prototype from which it was > >>derived? > >> > >>Jerry > > That's the other way around from what I guessed. Why do you want to do > that? It isn't usually worth it. We use analog Bessel Filters for their > nearly constant group delay in the pass band, sacrificing amplitude > response to achieve it. Symmetric FIRs have perfectly constant group > delay and are relatively simple to design, so why compromise? When an > FIR filter is derived from an analog Bessel prototype, the performance
^^^ (did you mean IIR?)
> is usually disapointing. The amplitude sacrifices still mar its > performance and its phase response is poorer than the prototypes. Unless > this is a homework assignment or an assignment from a boss you can't > reason with, do something more sensible.
As noted above, usually, you only design IIR filters from analog prototypes, not FIR. If the OP is constrained to using an IIR (e.g. by available processing power, need to adjust on the fly, etc.) but still wants "good" phase properties, then an IIR Bessel filter designed from an analog prototype might be the answer. I have also heard that the digital version loses some of the desirable phase/group delay characteristics of the analog prototype, but I believe it's still better than e.g. Butterworth in that respect.
Reply by Jerry Avins April 8, 20042004-04-08
bngguy wrote:

> hi! Jerry, > am trying to derive a digital filter from its analog prototype... > let me know if u have any leads.... > > thanks > > > Jerry Avins <jya@ieee.org> wrote in message news:<4074c6e9$0$1658$61fed72c@news.rcn.com>... > >>bngguy wrote: >> >> >>>does any body know how to determine the analog prototype of a bessel filter??? >>> >>>thanks >> >>Eh? Do you mean, given a digital Bessel filter (there are few reasons to >>want one), how can one determine the analog prototype from which it was >>derived? >> >>Jerry
That's the other way around from what I guessed. Why do you want to do that? It isn't usually worth it. We use analog Bessel Filters for their nearly constant group delay in the pass band, sacrificing amplitude response to achieve it. Symmetric FIRs have perfectly constant group delay and are relatively simple to design, so why compromise? When an FIR filter is derived from an analog Bessel prototype, the performance is usually disapointing. The amplitude sacrifices still mar its performance and its phase response is poorer than the prototypes. Unless this is a homework assignment or an assignment from a boss you can't reason with, do something more sensible. Jerry -- Engineering is the art of making what you want from things you can get. &#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;
Reply by Jon Harris April 8, 20042004-04-08
Try this:
http://www.crbond.com/papers/bsf2.pdf

(found by Googling for Bessel filter).

"bngguy" <loosepraje@yahoo.com> wrote in message
news:519f37cf.0404080750.2e62fa18@posting.google.com...
> hi! Jerry, > am trying to derive a digital filter from its analog prototype... > let me know if u have any leads.... > > thanks > > > Jerry Avins <jya@ieee.org> wrote in message
news:<4074c6e9$0$1658$61fed72c@news.rcn.com>...
> > bngguy wrote: > > > > > does any body know how to determine the analog prototype of a bessel
filter???
> > > > > > thanks > > > > Eh? Do you mean, given a digital Bessel filter (there are few reasons to > > want one), how can one determine the analog prototype from which it was > > derived? > > > > Jerry
Reply by bngguy April 8, 20042004-04-08
hi! Jerry,
          am trying to derive a digital filter from its analog prototype... 
let me know if u have any leads....

thanks


Jerry Avins <jya@ieee.org> wrote in message news:<4074c6e9$0$1658$61fed72c@news.rcn.com>...
> bngguy wrote: > > > does any body know how to determine the analog prototype of a bessel filter??? > > > > thanks > > Eh? Do you mean, given a digital Bessel filter (there are few reasons to > want one), how can one determine the analog prototype from which it was > derived? > > Jerry
Reply by Jerry Avins April 8, 20042004-04-08
bngguy wrote:

> does any body know how to determine the analog prototype of a bessel filter??? > > thanks
Eh? Do you mean, given a digital Bessel filter (there are few reasons to want one), how can one determine the analog prototype from which it was derived? Jerry -- Engineering is the art of making what you want from things you can get. &#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;&#4294967295;
Reply by bngguy April 7, 20042004-04-07
does any body know how to determine the analog prototype of a bessel filter???

thanks